Encyclopedia of Adaptations in Natural World

ENCYCLOPEDIA OFADAPTATIONS IN THENATURALWORLD

Adam Simmons

GREENWOOD PRESS

An Imprint of ABC-CLIO, LLC

Copyright 2010 by Adam Simmons

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Simmons, Adam.Encyclopedia of adaptations in the natural world / Adam Simmons.

p. cm.Includes bibliographical references and index.ISBN 978–0–313–35556–1 (hardcover : alk. paper) — ISBN 978–0–313–35557–8 (ebook)

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CONTENTS

Introduction xi

About This Book xiii

1 Making and Using Energy 1

Making and Using Energy—Human Invention 1Photosynthesis 3Chemosynthesis 6Catabolism 8Ectothermy 12Chemical Defense—Bombardier Beetle 14Chemical Defense—Devil’s Garden Ant 16Electricity 19Bioluminescence 21

2 Surviving the Elements 25

Surviving the Elements—Human Invention 25Thermophilic Bacteria—Surviving Extreme Heat 28Blood Antifreeze—Surviving Extreme Cold 31Mammal Fur—Surviving Extreme Cold 33Mangroves—Surviving Extreme Salt 35Lungfish—Surviving without Oxygen 38Melanin—Surviving Radiation 40Parasitism—Surviving Host Defenses 42Antibiotics—Surviving Disease 45Psychrophiles—Surviving Extreme Cold 47Anhydrobiosis—Surviving without Water 49Prions—Surviving Everything 51

3 Locomotion 55

Locomotion—Human Invention 55Bird Flight 58Insect Flight 60Running 63Swimming—Bluefin Tuna 66Jet Propulsion 68Parasitic Locomotion 70Pollination 72Bacterial Flagellum 75

4 Materials 79

Materials—Human Invention 79Silk 82Bone 84Chitin 86Feathers 89Skin 92Bio-ceramics 94Mucus 96Natural Glues 98Gecko Feet 100Resilin 103

5 Building Structures 107

Building Structures—Human Invention 107Termite Towers 109Trees 112Bird Nests 115Beaver Lodges 117Bee Nests 120Paper Nests 122Coral Reefs 124Luminous Gnat Traps 127Naked Mole Rat Burrows 128Diatoms 131Webs 134

6 Sensing the Environment 137

Sensing the Environment—Human Invention 137Vertebrate Eyes 140Insect Eyes 142Echolocation 144Electrosense 147Fire and Smoke Detectors 149Infrared Vision 151Jacobson’s Organ of Smell 153Odorous Genes—The Major Histocompatibility Complex 155Magnetic Sense 158Insect Antennae 160

viii CONTENTS

Specialized Eyes 162Mantis Shrimp Eyes 165

7 Communication 169

Communication—Human Invention 169Human Brain 171Human Language 174Plant Communication 177Bee Dance Language 180Bacterial Conjugation 182Culture 184DNA 187

Further Reading 191

Index 195

CONTENTS ix

INTRODUCTION

The ingenuity of the human race seemingly knows no bounds. From humblebeginnings we have built staggering monuments, made breathtaking art, splitthe atom, and conquered space. On the cosmic scale, all this has been createdin a blink of an eye—over a mere few thousand years in the planet’s4.6 billion-year history. Now in the twenty-first century we continue to pushthe boundaries, make new discoveries, and build more remarkable machines.

We are rightly proud of our achievements. Our inventions have made ourlives easier and more comfortable. Many diseases, once deadly, have now beenovercome with vaccines, antibiotics, and improved hygiene. The raw energiesof our universe have been tamed to provide us with controllable power, andwe protect ourselves from the extremes of the environment with intricatelyengineered cocoons.

We have come a long way since our first recognizable human ancestorswalked the earth some 2.5 million years ago. We sometimes forget, though,that we share our planet with many millions of other creatures—other animals,plants, bacteria, fungi, protozoa, viruses, and even tiny, single, self-replicatingstrands of protein. Many of these creatures are small and extremely hard tospot, but they are there and they have survived for much longer than we have.Their success lies in their own remarkable adaptations to this planet—perhapsnot always so noticeable as our own adaptations, but ingenious adaptationsnonetheless.

All life on earth is programmed to survive. And after some 3 billion years ofevolution it has become quite good at it—it has had to. On all sides, each andevery organism on earth is faced with danger. From the elements. From its

predators. Even from its own kind. After all this, it must then find food, water,and, ultimately, a mate if it is to successfully survive and pass on its genes.

As we delve into the huge array of life on earth we find truly ingenious,astounding, and downright weird adaptations that have allowed life to flourishin the most inhospitable of environments. Adaptations that allow organisms toperceive the world in more detail than our most sophisticated microscopes,telescopes, and scanners. Adaptations that allow organisms to move with suchspeed and agility that they make our advanced modes of transport look slug-gish. Adaptations that produce materials of such strength and flexibility thatwe have not come close to replicating them.

Over million of years of evolution, life has adapted well to the harsh condi-tions of our planet in exactly the same way we have. Human engineers tinkeraway at a rough plan, making tiny adjustments to hone their design to perfec-tion. Nature does the same. The evolutionary biologist Richard Dawkinsdescribed nature as a blind watchmaker. It may not see and plan the tinychanges it makes to its design, but it knows when something is working.

This is how evolution works. Physical and behavioral traits are coded for onthe genetic material, DNA, held within every cell of every living organism.Small mistakes and alterations in this genetic code that occur as organismsreproduce lead to tiny changes in the traits we see. Some of these changescan be harmful and result in the new individual dying earlier or producingfewer offspring than if the change had not happened at all. These deleteriouschanges in the gene pool will eventually be lost. Other changes, though, willbe beneficial. They will code for improved eyesight, greater physical strength,or a new behavior that gives an individual a competitive advantage over othersof its species. These changes will tend to be preserved in the gene pool. Overtime, these changes can be honed by natural selection to produce the special-ized adaptations we see in nature today.

Many adaptations have evolved that match or even surpass our own achieve-ments. Why else would today’s scientists be so keen in borrowing so much ofwhat has been created in nature? This book seeks to capture the most funda-mental of these adaptations, some of which may be familiar to you from distant(or perhaps not so distant) school days. Others will be completely new. I hopethat you will look on those you knew in a new light, and those you didn’t with adesire to know more.

The parallels of these adaptations with our own drive for survival are close.After all, humans are organisms like any other in this planet. We have muchmore in common with the other creatures who live on this planet than wemight think. Viruses, bacteria, single-cell protozoa, plants, and animals (our-selves included) are all driven to survive. It is from this race for survival thatmany remarkable wild designs have emerged.

xii INTRODUCTION

ABOUT THIS BOOK

As humans, we are aware of the great challenges to our own survival. Being ananimal like the many thousands of others on this planet, it should not come as asurprise that the challenges we face are those faced every day by every otherspecies on earth. This book is divided into seven chapters that group thesechallenges together:

Making and Using EnergySurviving the ElementsLocomotionMaterialsBuilding StructuresSensing the EnvironmentCommunication

Each chapter begins with a short history of the human achievements andinventions in that field that have led to our success. As the rest of the chapterwill show, though, evolution has created similar adaptations that match andsurpass our own. Each of these adaptations is set out in its own entry, withthe aim that the reader can dip into the book according to his or her interest—either for research or curiosity. At the end of every adaptation entry is ashort section called ‘‘Borrowing from Nature’’ that shows how human engi-neers, scientists, and inventors are directly taking what they see in nature anddeveloping it for the advancement of human endeavor.

Evolution and biology, like all the sciences, have their own jargon that can,to the lay person and expert alike, be baffling at times. I have therefore

attempted to keep jargon to a minimum and to explain those terms that I douse. Where possible, I use the English names for species, but I also includethe Latin name as well should the reader wish to research the subject further.For some adaptations there is no English name for the species that exhibitthem, so in those instances I have had to use the scientific nomenclature.

Perhaps unusually for a science reference book I have not included referen-ces for each entry, as they would have broken the flow of the narrative. Instead,I offer the interested reader a recommended reading list at the end of the ency-clopedia to further research the field. This list includes several of the keypapers and references I have used in writing this book. I have tried to give asmany readily available references as possible.

For each entry I have tried to describe the evolutionary advantage eachadaptation conveys rather than simply list and describe a series of biologicalcuriosities, fascinating though this would be in its own right. I hope that youfind adaptations both interesting and awe-inspiring. Even after many years ofstudy, evolution has a habit of always throwing up something that is trulyremarkable.

I would like to thank David Paige of ABC-CLIO/Greenwood Publishingfor his help, enthusiasm, and ideas during writing. I am also very grateful toKevin Downing of Greenwood for his help in getting the project off theground. This book would never have happened at all without the encourage-ment and friendship of Ross Piper, not to mention the useful discussions andsharing of ideas—thank you. Finally, and as ever, thank you to Maggie, Roy,and Beth for all their love and support.

xiv ABOUT THIS BOOK

1

MAKING AND USING ENERGY

MAKING AND USING ENERGY—HUMAN INVENTION

Without energy there is no life. Nature has come up with a myriad of ingeniousways of harnessing energy, which it uses to drive the various reactions criticalfor life. Controlling energy has been important to the success of humans, too.It has helped our ancestors survive inhospitable environments and has beenthe foundation of the many inventions that make our lives easier today.

Although humankind may not have always understood the processes thatunderlie the reactions that have produced useful energy, there is no doubtingthe skill in which energy has been harnessed and used to do work. At its sim-plest, humans have utilized the energy to be found in the elements, such aswind and water, and channelled it to our own ends through mills for drivingmachinery.

There are many human inventions that have led to the successful andcomfortable lives we lead today. The most fundamental of these has been theuse of fire. Since human ancestors first used fire some 1.5 million years ago,it has provided warmth and protection that allowed humans to move out fromthe warmer tropics and begin to exploit colder climates. Fire has even played akey part in the human diet. It has been used to make food sources safer, morepalatable, and more easily digested. Starch (an important source of carbohy-drate) found in plants is much easier to digest if it has been cooked and brokendown into the simple sugar, glucose.

Today, of course, another form of energy has taken over as the most impor-tant in our lives. It plays a role in nearly everything we do, and yet we rarelynotice its presence. Electricity provides energy for nearly all the tools,machines, and gadgets that make our lives easier and more enjoyable.

Most electricity is provided by our power stations, which rely on a fuel ofone sort or another to create heat to boil water, the steam from which drivesturbines that can generate electricity. Traditionally, fossil fuels are burned,but nuclear power stations work in the same way. Radioactive materials likeuranium decay and give off heat, which drives the power station. Althoughexpensive, nuclear power stations are very effective, reaching efficiencies ofover 90 percent compared with an average efficiency of 30–40 percent for fossilfuel power stations.

Heat-driven power stations are not the only way of generating electricity.More recently, solar panels have been developed that convert light energy toelectrical energy. They are made from a group a materials called semiconduc-tors, such as silicon embedded with tiny amounts of other materials, such asphosphorus and boron. Semiconductors are able to absorb light from the sunand store the energy contained within it. When most objects absorb light,the energy that is absorbed is simply given off as heat. (This is why objectsget hot in the sun.) Semiconductors are different in that they can absorb energyfrom the sun and release it as an electrical current.

The ability of solar panels to convert sunlight into electrical energy variesgreatly. A basic solar panel that can be obtained from a hardware store can con-vert about 15 percent of the light energy falling on it into useful electricity.The very best solar panels can convert 42.8 percent of the sun’s energy intoelectrical energy. We are still decades away from creating a solar panel thatcan convert 100 percent of solar energy into electrical energy, but if we doour energy problems could well be over.

We can only speculate about the future, but the answer probably lies in afamous equation that nearly everyone knows but few understand—Einstein’sE = mc2. This simple looking equation shows that the energy (E) stored in anobject is equal to its mass (m) times the speed of light (c) squared. The speedof light is a massive number, which means that a lump of any substance, evena tiny amount, contains a huge amount of energy. Einstein’s equation madeus realize that a huge reserve of energy is at our fingertips in the very atomsthat make up every single thing. The atomic bombs dropped on Hiroshimaand Nagasaki were the first real demonstration of the power of the atom. Fromonly one-half of 1 percent of one pound of uranium so much energy wasreleased that a city was flattened and many of its inhabitants were killedor injured.

The energy contained in the atom is awesome, but the difficulty comesin releasing it in a controlled way. If we could control these reactions infusion reactors, one day we could provide the whole of the world’s energydemands from seawater. The energy contained in 150 gallons of running watera minute would be enough to produce all the energy that is used in the UnitedStates today.

There is no doubt that the mastery of different energies has been the key tothe success of the human species. But nature, too, has made use of the physical

2 ENCYCLOPEDIA OF ADAPTATIONS IN THE NATURALWORLD

properties of energy to its own ends. As we delve into the many and variedadaptations found in nature we see that not only has evolution helped tamethe powerful energies found in this universe, but it has gone further and putthem to such fascinating, intricate, and elegant uses.

PHOTOSYNTHESIS

By harnessing the energy of the sun,plants, algae, and even some bacteria canmake the basic nutrients that are essentialfor life. Not only does this remarkableprocess benefit these living power sta-tions themselves, but it is also the basisfor much of the energy needed for lifeon earth to thrive. Thanks to the vastswathes of green plants across the world,on land and in water, we can all eat andbreathe. The ingredients for photosyn-thesis are common enough. Water andcarbon dioxide are combined to produceglucose and oxygen. Glucose is a univer-sal source of energy that powers all theprocesses that keep a plant alive (as wellas animals such as humans, which is whywe eat plants).

The challenge lies in getting the energy to drive the process of convertingthe ingredients into the end product. The energy source for photosynthesis islight emitted by the sun. It is not a straightforward process, though, andrequires an impressive feat of natural engineering that is so successful thatphotosynthesis has become one of the most widespread adaptations onthe planet.

There are two key stages in photosynthesis. The first stage harnesses thesun’s energy into a usable form. The second stage then uses this energy tomake the energy-packed glucose molecules. Both of these stages occur at themolecular level, but really we can think of the molecules involved as minisculerechargeable batteries. Photosynthesis is about moving energy from one ofthese microscopic batteries to another—one battery is used to charge up thenext, and so on. The first stage in photosynthesis is therefore about toppingup one set of tiny molecular batteries with energy from the sun.

The ‘‘batteries’’ that absorb the sun’s energy are light-absorbing mole-cules in the plant’s leaves called chlorophyll, which is a green pigment thatgives the leaves their characteristic color. Rather than simply getting hotterwhen it absorbs sunlight, chlorophyll is able to absorb the energy and storeit until it can be used later. The energy absorbed by chlorophyll is put to

MAKING AND USING ENERGY 3

Photosynthesis in the chloroplasts of plantsconverts water (H2O) and carbon dioxide(CO2) into carbohydrate (C6H12O6), which isused by the plant as an energy source, and oxy-gen (O2). [BSIP / Photo Researchers, Inc.]

two important uses. First, it is used to break down water, one of the twoingredients in photosynthesis. Water is made up of hydrogen and oxygen,but for photosynthesis the plant is only interested in the hydrogen part.The plant doesn’t need the oxygen part, so when water is broken down theoxygen is simply expelled by the plant. This is why oxygen is produced as aby-product of photosynthesis—it is by this lucky accident that we are ableto breathe!

Once hydrogen is made from breaking down water it is then put to gooduse. Energy stored in the chlorophyll is used to pump the hydrogen througha special type of molecule that works much like a water mill. In a water mill,water drives a wheel that turns a machine for grinding flour. In the hydrogen‘‘mill,’’ hydrogen drives the molecular mill that is used to charge up anothermolecular battery with energy. This particular molecular battery is a veryimportant molecule that is used in a number of reactions inside the cells ofliving organisms. It is called Adenosine Tri-Phosphate (ATP).

So far, the plant has absorbed energy from the sun and used it to charge up acritical molecular battery called ATP. This then is used to drive the secondstage of photosynthesis—using the energy stored in ATP to make glucose.

Glucose is packed with energy—that it is why it is so useful to the plant.It can be used as an energy source, and it can be stored easily to keep energyin reserve. Glucose is produced from carbon dioxide, the second ingredientof photosynthesis. Carbon dioxide has very little energy—it is a little like a flatbattery. Through a series of chemical reactions, this flat battery is graduallytopped up with energy, provided by ATP, until it is fully charged in the formof glucose. The process of converting carbon dioxide to glucose is called theCalvin Cycle.

Having now made the energy-packed glucose the plant can now put it togood use. Glucose can be used to power all the processes that go on in plantsto allow them to stay alive—processes like reproduction, defense, and growth,to name but a few. Glucose itself is a simple molecule—one of the small mole-cules we typically think of as sugar. In plants (and indeed in animals) it is oftenconverted to carbohydrate, which are long chains of these simple sugar mole-cules. Root tubers like potatoes and carrots are huge stores of carbohydratekept in reserve for when a plant may need to convert them back into useful sug-ars. From this amazing adaptation, then, the plant’s entire life can be carriedout without the need to consume anything else. All its energy is available fromjust water, carbon dioxide, and a healthy amount of sunlight.

This process of photosynthesis that creates useful energy from the sun hasbeen central to the flourishing of nearly all life on earth, both in the food thatall organisms eat (carbohydrate) and in the air that they breathe. Of course, it isnot for the good of other organisms that photosynthesis has evolved. Photo-synthesis is found in plants, algae, bacteria, and lichens and has allowed themto conquer nearly every corner of the earth. By making their own energy andnot having to rely on other organisms to provide them with a tasty snack,


plants, algae, and bacteria have become hugely successful. As a result, ourplanet is carpeted with plants, lichens, algae, and bacteria, all of which relyon photosynthesis and all of which make for a truly green earth.

Although we normally think of plants when we think of photosynthesis, itwas actually the humble bacteria that first evolved the ability to make foodfrom the sun. These pioneering bacteria did well and flourished, as they dotoday, until a very strange and unique partnership was formed. Once lifeemerged on this planet some 3.7 billion years ago, organisms were made onlyof one single cell, much like the amoeba of today. Some of these cells—bacteria—could make their own food from the sun’s energy in much the sameway we have described above.

So how did plants evolve this same ability as bacteria to capture energy fromthe sun’s radiation? There is no definitive answer, but the most compellingevidence points to what is known as the ‘‘endosymbiotic theory.’’ In essence,this theory describes how photosynthetic bacteria were swallowed up by earlyplant ancestors and formed with them a mutually beneficial (symbiotic) rela-tionship. Like plants today, photosynthesizing bacteria would have been preyto other organisms and would have often been eaten. The theory states thatat some point in time, a bacteria was swallowed by another single-celled organ-ism but not digested—it remained inside its would-be attacker unharmed. Bychance, both the bacteria and the predator profited from this unexpectedunion. The bacteria was protected by living inside another organism, and thepredator could make use of the food the bacteria could produce from thesun. Over time both organisms evolved into one living organism, producingthe first ancestor of today’s plants.

As these single-celled plant ancestors evolved into the multi-cellular plantswe see today, they retained the photosynthesizing bacteria that have evolvedinto specialized structures called chloroplasts. Thus, plants never directlyevolved photosynthesis for themselves, but rather acquired the ability fromswallowing a bacteria many thousands of years ago—an amazing example ofhow opportunistic nature can be! Thanks to this happy cohabitation of abacterium inside a plant it’s probably fair to say that photosynthesis is nowone of the most important adaptations to have evolved on this planet.

Borrowing from Nature

Plants have long been a source of inspiration for engineers. Solar panels areimproving all the time and are already outstripping the efficiency of plants atconverting the sun’s energy. A basic solar panel can convert about 15 percentof the light energy falling on it into useful electricity. The very best solarpanels can convert 42.8 percent of the sun’s energy into electrical energy.In contrast, the maximum conversion rate of plants is around 25 percent incommercial crop species such as wheat, but most plants only convert around3 percent of the sun’s energy into food.


This may suggest that human engineering has outstripped nature, but man-made solar panels are expensive and currently require more energy to makethan they can generate. Plants, on the other hand, are entirely self sufficient.The energy they make allows them to grow and reproduce in an ongoing andindefinite cycle of life. Scientists are therefore spending time in developingartificial photosynthesis systems that can produce an energy supply from waterand carbon dioxide. In early 2009, researchers from the U.S. Department ofEnergy’s Berkeley Laboratory took a significant step forward in this goal.They discovered that microscopic crystals of cobalt oxide can control thewater-splitting reaction central to photosynthesis. This completes only halfthe puzzle, of course, but if the rest can be achieved we may have access to aninexhaustible supply of energy.

CHEMOSYNTHESIS

Until recently, it was thought that all life on earth is dependent on the foodproduced by plants, bacteria, and algae through photosynthesis. In the last30 years, though, as we have explored our planet more thoroughly, we havediscovered self-sustaining oases of life where there is no light whatsoeverwhere photosynthesis could not possibly take place. In seemingly uninhabit-able environments like the deep ocean or deep within the rocks that make upour planet, whole communities of species flourish and thrive. How is this featachieved without light to supply the energy?

In plants, carbon dioxide and water are broken down using energy from thesun and reformed to make carbohydrate—the body fuel for all life on earth.

The key to this reaction is that someenergy (from the sun) is needed to makethe reaction happen. This is much likewhat happens when something burns.A candle wick does not catch fire sponta-neously, but rather an external supply ofheat energy (like a lighted match) isrequired to start the process off. Somereactions, however, do occur spontane-ously. Hydrogen and oxygen, for exam-ple, will always react with each other tomake water without any extra energy tokick things off. Some ingenious bacteriaare able to control spontaneous reactionslike these to make carbohydrate in a pro-cess called chemosynthesis.

With the right ingredients, certainbacteria can make carbohydrate withvery little effort at all. The ingredients


Deep ocean tube worms (Vestimentifera) haveevolved a symbiotic relationship with bacteriathat can convert carbon dioxide and the hydro-gen sulfide emitted by hydrothermal vents intocarbohydrate. [Dr. Ken Macdonald / PhotoResearchers, Inc.]

are very unusual, though, and are indeed quite toxic to most organisms. Yetsome industrious bacteria are quite at home with these toxic materials and havemade a very successful way of life with them. One group of bacteria calledThiobacillus makes use of hydrogen sulfide as its basic food-making ingredient.This is the gas released from geysers and hot springs that smells of very badeggs. Other bacteria (Nitrosomonas) use ammonia as a food source, and others(such as the Methylococcaceae family of bacteria) use methane. All these bacteriaallow either hydrogen sulfide, methane, or ammonia to react with water andcarbon dioxide to produce carbohydrate.

Hydrogen sulfide, methane, and ammonia are all quite rare. Wherever theyare found, though, there will always be a colony of bacteria to exploit it. Oftenthese bacterial fuels are found where light cannot reach, which means these bac-teria can exploit an untapped niche free from the competition of other—photo-synthetic—bacteria, which is why chemosynthesis is such a successful adaptation.

In 1977, a deep ocean submersible called the Alvin discovered a highlydiverse ecosystem of life living some 8,000 feet (2,500 m) below sea level. Withno life-giving sunlight penetrating this far below the surface, it was a mysteryas to how this life was supported. The answer was revealed when it was noticedthat the greatest density of life was found clustered around huge natural chim-ney stacks that emerged from the ocean bed. The stacks (or black-smokers asthey were called due to the huge black clouds they spouted) were releasing asteady stream of hot water containing hydrogen sulfide. The same effect is seenon land in geysers or hot springs.

Bacteria that are capable of producing food from this abundance of sulfurflourish around these black-smokers. Like plants on land, these independent foodfactories support a huge variety of life that feeds off them, including shrimp,clams, and tube worms. Indeed, after exploration scientists found that in a tinyarea of only 225 square feet (21m2—about the same size as a small house) 798 spe-cies could be found, including 171 families and 14 phyla. This is an extremelydiverse array of life for an area thought previously to be just a barren desert.

This fantastically diverse ecosystem is principally supported by one type ofbacteria. For the most part,Thiobacillus bacteria are found as free-living organ-isms floating near the seabed. Some species, though, have made fascinatingpartnerships with other organisms, such as tube worms (Vestimentifera) andclams (Vescomyidae). The tube worm is particularly intriguing. It is an animal,but it has no mouth and no gut—it is able to survive seemingly without eating.Instead of the normal digestive tract we find in animals, this remarkable crea-ture has a simple internal bag (called a trophosome) whose cells are packedwith chemosynthetic bacteria. Unlike the free-living bacteria that can makecarbohydrate from hydrogen sulfide and carbon dioxide alone, these bacterianeed oxygen as well. The tube worm provides the bacteria with the oxygenthey need, and the bacteria return the favor by producing the carbohydrateneeded to feed the worm. This could be one of the few examples of an animalthat doesn’t need to feed on another organism to survive.


Away from the ocean floor, and if you are unlucky enough to stumble intothem, there are some caves on this planet that are covered in a thick mucus,which are filled with a noxious gas and which drip corrosive acid on any visitor.One such cave is the Cueva de Villa Luz (‘‘the cave of the lighted house’’) insouthern Mexico. Like in the ocean, hydrogen sulfide leaks from the rocksand into the cave, and, just like in the deep-sea, bacteria exploit this readysource of food. It is in this cave, though, that we can fully see the second partof the chemosynthesis reaction. Whereas plants release oxygen as a wasteproduct of photosynthesis, the mucus-cave bacteria excrete sulfuric acid.This is a very strong acid that eats away at the limestone of the cave and makesit bigger and bigger. This is a bacteria that can directly modify its own envi-ronment! So far, the bacteria have cut out 1.2 miles (2 km) of rock to makethe cave.

Again, a whole ecosystem is supported by the food produced by the sulfur-digesting bacteria. Insects, spiders, and even bats thrive in this lightless envi-ronment thanks to the bacteria, and all of these organisms have evolved towithstand the acid that eats away at the walls. The spiders are even able tomake webs that survive the acidic conditions, which still mystifies scientiststo this day. This is truly a fascinating cave that may yet still hold amazingsecrets of which we are not aware. Some scientists believe that if bacteria cansurvive in these conditions on earth, then similar communities may dwellunder the rocky surface of Mars. This is not too far fetched a theory. Geologi-cal drilling in Washington State revealed bacteria surviving in solid rock some5,000 feet (1500 m) underground.


Bacteria that feed from toxic chemicals and convert them into safer wasteproducts are being explored to clean up toxic waste dumps. The first bacteriathat was used to treat sewage in the 1990s was Dehalococcoides ethenogenes. Thesame bacteria is also used to remove chlorine from carcinogenic waste, render-ing it safer. Thiobacillus is perhaps the most widely used bacteria, though, beingable to digest toxic heavy metals. Other bacteria have been used to clean up oilspills and treat a particularly dangerous class of cancer-causing chemicalscalled aromatic hydrocarbons.

CATABOLISM

Energy is required by all living organisms for them to move, grow, repro-duce, repair themselves, and indeed do all the things that are needed to stayalive. Energy is available from the food that an organism eats or makes for itselfby photosynthesis or chemosynthesis. The challenge is then to convert thisenergy into a useful form to power their cells.

In all life on earth food is broken down—in a process called catabolism—in a way that creates a particularly useful molecule called Adenosine



A scanning electron micrograph of a mitochondrion. These organelles are foundinside nearly all living cells and are involved in breaking down carbohydrate to releaseenergy to fuel the cell. [Professors Pietro M. Motta & Tomonori Naguro / PhotoResearchers, Inc.]

Tri-Phosphate (ATP). ATP is what is known as a biological energy carrier—itliterally carries energy to where it is needed. This molecule is used to power allthe processes that go on inside an organism’s cells. Whereas humans havemade use of electricity as the main source of power for our inventions, natureuses ATP. So really, we can think of ATP as the universal battery that is usedto power all of life on earth.

All organisms break down their food to produce ATP, but there are manyweird and wonderful ways that have evolved to achieve it. Many catabolismshave evolved to exploit every environment on the planet. Thanks to theseamazing adaptations, many organisms can survive and thrive in some of theharshest conditions on earth.

All animals, humans included, get most of their energy from carbohydrate.This is broken down in our cells with oxygen to make ATP, carbon dioxide,and water. This is why we need to breathe oxygen—it is essential for ourbodies to get energy from our food. Catabolism that uses oxygen to get energyin this way is called aerobic respiration. This form of respiration takes place inthe hundreds of very tiny structures called mitochondria that are found insideour cells. These mitochondria work like miniature power stations, taking fuelfrom food and converting it to energy in the form of ATP.

Mitochondria evolved in much the same way as chloroplasts in the leaves ofplants; that is, they evolved from bacteria. These bacteria existed as free-livingorganisms millions of years ago until a very strange union was forged withanother single-celled organism. We are talking about a time when all organ-isms were made up of just one cell. At this time, along with bacteria thereexisted single-celled organisms that were the very ancient ancestors of today’sanimals and plants. These animal ancestors could eat other organisms byswallowing and digesting them. At some point, though, an animal ancestorswallowed a bacteria and instead of digesting it, kept it alive inside its single-celled body. When our single-celled ancestors evolved into multi-cellularplants and animals, they retained the bacteria inside their cells, and theseevolved into mitochondria.

What is fascinating, though, is why this unusual union benefitted both ouranimal ancestor and the bacteria living inside it. For the bacteria, perhaps itis a little easier to understand. Living inside another organism gives it protec-tion and a constant supply of food and minerals. For the single-celled animalancestor, the benefits are a little more subtle. When life first emerged on earthsome 3 billion years ago there was no oxygen at all. All single-celled life got itsenergy from the other gases that swirled around the atmosphere—nitrogen,methane, sulfur, and water vapor. Once photosynthesis evolved in single-celled plants, though, oxygen began to be released into the air.

Oxygen is toxic gas. Even to this day our bodies need clever defenses to pro-tect our cells and tissues from the corrosive gas despite its important role inkeeping us alive. Early bacteria were the first organisms to evolve to make useof oxygen as a way of making energy. As it happens, aerobic respiration is a


much more efficient form of catabolism than using any other gas. Bacteria thatcould use aerobic respiration, therefore, did very well with this new adaptation,gaining a competitive advantage over other bacteria. Of course, any otherorganism that housed a few of these bacteria could benefit from their new andefficient way of making ATP. What’s more, the bacteria could help protecttheir host from the toxic effects of the poisonous, oxygen-rich environment.

So again we see that a highly efficient adaptation has evolved in a veryopportunistic way. Thanks to a union that evolved between two single-celledorganisms millions of years ago, all animals and plants are able to convert theirfood to energy with great efficiency.

Aerobic respiration is not the only way of releasing energy from food,though. We are familiar with species that can break down carbohydrates, fats,and proteins for energy, but less well known are the few bacteria that call toxicchemicals food. In principle, anything can be used as a food supply. There aresome bacteria that use some unusual chemicals as food. Pseudomonad bacte-ria, for example, can break down the explosive nitroglycerin and TNT forenergy. One group stands alone, though, in its ability to break down toxicwaste for food, a group of bacteria called Rhodococcus.

There are 12 species of Rhodococcus and they can be found in a wide range ofenvironments, including soil, rock, boreholes, groundwater, ocean sediments,animal dung, insect guts, and in plants, animals, and humans. These bacteriahave the unexpected ability to digest a wide variety of highly toxic compoundssuch as coal, petroleum, steroids, chlorinated phenolics (used in the plasticsindustry), certain acids, and even the drug heroin. How are they capable ofbreaking down such a range of toxic chemicals?

First, they have evolved an outer membrane that not only is capable of with-standing the toxic nature of their food, but that also helps the bacteria stick towhatever it is attempting to devour. Second, these bacteria have evolved toproduce the necessary enzymes to break down their toxic food. (An enzymeis a biological molecule whose job it is to break down other molecules.) Whatis incredible, though, is that the genes that control the enzyme production canbe transferred between these bacteria. This is achieved by the bacteria makinga biological bridge from one individual to another and passing key parts oftheir DNA to each other. Specifically, they transfer the pieces of DNA thatare specifically involved with their amazing catabolic abilities. Thanks to thisability to share DNA, each species can carry a whole library of DNA thatcan produce the right enzyme for the right chemical—an amazing example ofteamwork having evolved in one particular group of bacteria. It is easy to seethe benefit of such an adaptation. Using food that would harm other organ-isms opens up a huge niche to be exploited.


The ability of different bacteria to catabolize unusual and often toxic mate-rials is of great use in industry. Industrialization across the globe has led to


hugely elevated concentrations of metals in soils, which can have catastrophiceffects for growing plants. The presence of bacteria known to be digesters ofcertain toxic metals can be used as indicators that soil quality is deteriorating,which can be an important early warning system particularly for soils usedfor agriculture. What’s more, as we’ve seen above certain bacteria can breakdown toxic chemicals, making contaminated areas safer for humans and otherwildlife. In addition to bacteria that break down nitroglycerin, bacteria havebeen used to digest cancer-causing chemicals, tar, ammonia, and even radioac-tive waste. The remarkable ability of these tiny organisms to withstandnormally uninhabitable environments and even use toxic waste as food hasallowed humans to clear up spills that would otherwise have had serious effectson local ecosystems.

ECTOTHERMY

All organisms have an optimal body temperature. This is because insideevery organism, thousands of chemical reactions are firing away to keep italive. These chemical reactions are very dependent on temperature. If the tem-perature is too cool, the reactions don’t happen quickly enough and webecome sluggish. If the temperature becomes too high, the tiny molecules(enzymes) that control these reactions start to break down and death rapidlyfollows. It’s all about balance. Most of these reactions have an optimal temper-ature of around 100°F (38°C), which is why our own bodies are kept at aroundthat temperature.

Humans have little problem staying warm. Even in very cold conditions, ourbody regulates its temperature to a constant 98 degrees Fahrenheit.We have this trait in common with all mammals and birds—we are all warm-blooded animals. We are all endotherms. Being able to regulate body temper-ature provides a great advantage. Endothermic animals can keep their internalreactions ticking over throughout the day regardless of how hot or cold theenvironment is. This means that they can be active at all times of the day,making them free to forage for food, seek out mates, and care for their youngwhenever they need to.

There is a cost to this freedom, though. To maintain a constant body tem-perature, warmblooded animals need to generate heat constantly. Likewise,mechanisms to cool down are needed when things get too hot. All this takesenergy, and quite a lot of it. In fact, around 80 percent of the food that warm-blooded animals eat is used up in maintaining their body temperature. Thatmeans that a lot of our waking hours are used to gather food. Some small,active birds like sparrows and finches need to eat almost constantly to stay alivesimply because so much energy is used up to keep warm.

There is another way, though. Most animals, including reptiles, amphibians,fish, and arthropods (insects, spiders, crustaceans, and the like), are cold-blooded, or ectothermic. These animals have less control over their body


temperature. They need to absorb heat from their surroundings before theirbodies are warm enough for their internal reactions to start firing. Thus, theytend to be active only during the day when they can get heat from the sun,although this is by no means exclusive.

Most ectothermic animals can therefore be found basking in the sun on hotrocks during the day. Having a good place to warm up is an important com-modity. In many species there are fierce fights for the best sunbathing spots.Male side-blotched lizards from California will fight over the hottest rocks inthe desert. Similarly, male speckled-wood butterflies from Europe fight overthe sunniest spots in otherwise shady woodland. In both of these species, andin many others, the victors not only get the warmest location in which to bask,but also the pick of the females who are attracted to the best sunbathing spots.

This may sound like a primitive solution to the problem of getting enoughenergy to move around, but that is far from the truth. The cold-blooded wayof life has been extremely successful. Of known animal species, 99 percentare cold-blooded and only 1 percent is warmblooded. What’s more, cold-blooded animals show just as complex and fascinating behaviors as their warm-blooded cousins. As none of their food is wasted on simply keeping warm,ectotherms can focus on much more important behaviors, such as finding amate and caring for their young.

Living with cold blood does not mean simply sitting in the sun and warmingup before setting out to perform the day’s activities. Many cold-bloodedanimals are very efficient at converting the sun’s energy into warmer body tem-peratures. One of the best is the leatherback turtle (Dermochelys coriacea), a hugemarine turtle that ranges through every ocean of the planet. You might thinkthat such a far-ranging animal would be at the mercy of the large variationsin temperature from tropical to arctic oceans, especially when you considerthat it is capable of diving down into near-freezing waters some 1,000 feet(300 m) below the surface of the water. The fact is, though, that the leather-back can maintain a steady body temperature of 77°F (25°C) or higher wher-ever it swims. This is some 31.5°F higher than the average sea temperature of45.5°F (7.5°C).

The leatherback achieves this remarkable feat through a series of adapta-tions that are designed to generate and maintain body temperature. Like mostectotherms, the leatherback can warm up by basking. Its huge carapace isblack in color, which absorbs heat energy, so a few hours in the sun can rap-idly get its body to optimum temperature. But what about the chilling effectof the sea? Apart from when it needs to lay its eggs, the leatherback neverleaves the water. For most animals, ourselves included, this would lead tosignificant cooling down. The leatherback gets around this problem withsome neat adaptations.

The trick is to keep heat in the body. Much heat is lost in animals when theheat in warm blood that is pumped to the extremities (flippers in the case of theleatherback) is lost to the cooler surrounding ocean. The leatherback avoids


this by making sure warm blood does not arrive at its flippers in the first place.It does this by a clever arrangement of its blood vessels at the base of itsflippers. Warm blood from the body is carried in arteries that run parallel tothe veins carrying cool blood back from the flippers. Because the arteries andveins run next to each other, the warm blood heats up the cool blood. In effect,the precious warmth of the turtle is recycled inside the body—it never gets to aplace where it can be lost to the elements. This is quite a common adaptation.It is through this ingenious method of internal heat engineering that manyanimals stay warm—it is why penguins do not lose all their heat through theirfeet perched on the frozen ground. It is a simple evolutionary solution to theproblem of fighting the cold, but it is one that has allowed a huge diversity ofanimals to colonize cold climates.

The arrangement of blood vessels helps, but it will not stop the leatherbackfrom cooling down indefinitely. Unusually for a reptile, the leatherback has athick (7 cm) layer of fat just under its skin that helps keep the heat in. This fatis a useful insulator that prevents heat being lost from the body, but it hasanother hidden property. It is actually a specific type of fat called brown fat.This type of fat has the remarkable ability to store heat that is either absorbedfrom basking or generated by the powerful swimming muscles. The heatstore can then give it out again when the body starts to cool. It is believedthat it is the presence of brown fat that allows the leatherback to maintainsuch a high temperature without needing to metabolize food. The leather-back, therefore, has all the benefits of both the warmblooded and cold-blooded ways of life without the drawbacks of either. It truly is theperfect ectotherm.


Although it has not directly been influenced by nature, the counter-currentheat exchange mechanism used to preserve heat in leatherback turtles is widelyused in engineering to preserve heat or control temperature. Man-madecounter-current heat exchanger work in exactly the same way as in nature.Pipes containing cold and hot fluids are placed next to each other, but withthe fluid flowing in the opposite direction. Heat is transferred from one fluidto the other. This is a perfect example of evolution and human inventionarriving at the same adaptation independently.

CHEMICAL DEFENSE—BOMBARDIER BEETLE

When it comes to protection from predators, sometimes attack is the bestform of defense. This is a trait employed by many animals, plants, and bacteriathat otherwise look very vulnerable to predation. One of the most effectiveforms of defense is to use toxic chemicals that debilitate potential predators.We are very familiar with the stings of bees and wasps, but these are just the


tip of the iceberg when it comes to venomsand poisons that have evolved in the long-standing chemical wars in nature. Some ofthe chemicals that have evolved and whichare deployed against potential attackers cancause pain, swelling, blistering, numbness,vomiting, and even seriously raising or low-ering blood pressure. One species, though,goes to the extreme of mixing a cocktail ofreactive chemicals in its own body beforereleasing it on an unsuspecting predator.

Bombardier beetles (Brachinus) are smalland unassuming looking insects being onlyabout 1 cm long. Although they can fly, bombardier beetles, like otherground-dwelling beetles, take a little while to prepare themselves for flight.Anyone who has seen ladybugs take off will know that they first have to openout their hard wing casings (called elytra) and then unfurl their wings beneath.Under attack, a beetle cannot afford this delay, so bombardier beetles haveevolved another defense mechanism that allows them time to escape.

Beneath the bombardier beetle’s plain exterior lies a powerful chemicalweapon to strongly discourage potential predators from taking too close aninterest. Within its abdomen are two glands that produce two highly noxiouschemicals—hydroquinone and hydrogen peroxide. They are unpleasantenough chemicals on their own (anyone who has bleached their hair blondewill attest to the eye-watering properties of hydrogen peroxide), but this isn’tenough for the bombardier beetle.

When the beetle is threatened, both chemicals will flow from their glandsinto a main reservoir, which in turn feeds into a reaction chamber. The reac-tion chamber is covered with specialized cells that produce and releaseenzymes (the molecules that control biological reactions) that break downthe hydroquinone and hydrogen peroxide into smaller molecules. These reac-tions produce a huge amount of heat energy (more than 210°F [100°C]) thatvaporizes the chemicals, adding to their potency. The pressure increases untilthe hot and noxious chemicals are violently forced from an opening on thetip of the bombardier beetle’s abdomen with an audible ‘‘pop’’ and into theface of a predator. This jet of chemicals can have a devastating effect onpotential predators. It can certainly cause serious pain on mammal and insectpredators, and some small predators can be fatally wounded by the defense.Even curious collectors can have their skin badly burned if they don’t handlethe insect with care.

Given the potent weapon housed within the bombardier beetle’s abdomen,there is an understandable number of safeguards to ensure the beetle doesn’tkill itself with a misfiring explosion. The valve between the reservoir and thereaction chamber is one way, so there is no chance of the reacting chemicals


A bombardier beetle, Brachinus sp.[Richard Parker / Photo Researchers, Inc.]

flowing back into the beetle’s body; the only way is out and into the face of anattacker. For this reason, the beetle must empty the reaction chamber beforetopping it up with new chemicals—the valve will only open when the reactionchamber is clear. The reaction chamber itself is thickly walled to prevent thechemicals from rupturing the beetle’s own body. Despite these necessaryprecautions, the whole process can be achieved in a fraction of a second.One abdomen full of superheated chemicals can be expelled at an attackerin up to 30 controlled bursts. Each burst can send a spray up to 20 cm.

Ground dwelling beetles like the bombardier beetle can come under attackfrom a number of potential enemies, not least of which are ants that scurryover the ground and will attack more or less anything moving. Ants are smalland hard to shift, which is why the bombardier beetle has evolved to be highlyaccurate with its chemical attack. The tip of the abdomen of these beetles ishighly mobile so it can direct a deadly accurate burst to wherever the dangerlies. Evidence shows that it can target a predator (like an ant) that has grabbedhold of particular leg. Not only can bombardier beetles target which leg isbeing attacked, but even which segment. It can even aim at predators attackingits back. This is far from being a crude weapon. What remains a mystery,though, is how the bombardier beetle avoids scorching its own body in theseattacks. Whatever the mysteries remain with this remarkable insect, it hasfound an incredible method for dealing with predators who could kill an other-wise defenseless animal.


Teams from the University of Leeds in the United Kingdom are learninghow the bombardier beetle can spray its liquid so far and so accurately. Repli-cating how the bombardier beetle fires its chemical cocktail, the team has beenable to fire pulses of hot water over distances of up to 13 feet (4 m) and hasbeen able to control the size of the droplets in the spray. The technique hasapplications for inhalers, needle-free injections, fuel-injection systems inengines, and as fire extinguishers. The fire extinguishers could be especiallyneat. The Leeds team’s system allows for control of the droplet size so thespray to put out the fire can be tailored to the circumstances.

Other teams are exploring the bombardier beetle’s ability to produce a hotchemical reaction for use in the aviation industry. This could provide a usefulanswer to the problem of how to reignite a gas turbine engine that has cutout, not an easy feat when the temperature outside could be as low as minus58°F (−50°C).

CHEMICAL DEFENSE—DEVIL’S GARDEN ANT

For many species, defense means growing some form of physical protection.Nature is full of species with tough shells, sharp spines, or foul-tasting


chemicals to deter predators. Some species, though, have evolved a mutuallybeneficial partnership that involves both species protecting each other. Antsare well known for the mutual partnerships that they have evolved with otherspecies. Many ant species will tend and protect certain species of plant inexchange for food and shelter. To achieve this, ants tend to use the energyreleased by chemical reactions to deter predators of their host plant. Chemicalsproduced in their bodies can burn and irritate any animal who happens tothink about browsing on an ant-protected plant. One species, though, hastaken this protection to the extreme, using chemical energy not only to deterpredators, but also to take care of their favorite plant’s competitors as well.

The devil’s garden ant, Myrmelachista schumanni, is a small ant that lives inthe Amazonian rainforest of Peru. Like many ants, it has formed a closerelationship with one species of plant—in this case, the tree Duroia hirsuta.So diligent is the devil’s garden ant in looking out for its host tree that it canhelp cultivate an entire stand of some 600 Duroia trees to the exclusion of anyother plant species. This is a remarkable achievement given the extraordinaryplant biodiversity in the Amazonian rainforest. Everywhere else in the rainfor-est this same area of land would be covered by hundreds of different plant spe-cies. Indeed, so unusual is this phenomenon of an area being dominated by oneplant species that local legend tells of the stand being created by an evil spirit.This is how these crops of Duroia have come to be known as ‘‘devil’s gardens.’’

So how does such a small ant engineer such an otherworldly feat of garden-ing in the most species-rich environment on the planet? Like many ants thatform these mutualisms with their host plants, the devil’s garden ant will pro-tect Duroia from herbivores. They will attack and possibly kill other insectsthat attempt to eat the leaves of the host plant. The ants will also spray largerherbivores with formic acid, an irritant, to discourage them from takingfurther bites out of their host tree.

Direct defense against herbivores will certainly help Duroia flourish, but itcannot explain why no other species of plant grows in the devil’s gardens.To achieve this, the devil’s garden ant takes a more direct approach with otherplant species that happen to be growing nearby. The devil’s garden ant can rec-ognize which plants are Duroia and which are of a different species. When itfinds a non-host species, ants will climb up on to the leaves and bite a hole inthe tissue. The ant will then insert its abdomen into the hole and squirt a dropof formic acid into it. The formic acid spreads through the veins of the leafand will, within a few hours, cause necrosis—the death of the tissue. This hap-pens on a massive scale, and soon any plant that is not Duroia will be bereft ofleaves and its means for making food. Established trees may take a while todie, but once aDuroia stand is established the devil’s garden ant will keep it clearof other species by killing off any unfamiliar seedlings as soon as they emergefrom the soil.

Freed from competition from other plants, Duroia trees flourish. Mostimportant for Duroia is that is can grow out of any shade from larger trees.


This allows it to get more light, which makes it more productive and which, inturn, allows for more rapid and healthy growth. The ants gain from this rela-tionship because it is within specially modified Duroia stems, called domatia,that they live. More trees means more domatia in which to live and rear young.Furthermore, the ants carry out other farming activities inside the domatia.This time, instead of cultivating a crop of trees, they farm livestock, or at leastscale insects that live on the sap of the Duroia. The ants look after these scaleinsects and feed off their honeydew—a sugary, sweet waste product secretedfrom the scale insect’s abdomen.

A mature stand of Duroia can support a very large colony of ants, althoughthis one colony will have been started by just a single female. The devil’s gar-den ant queen will colonize a single, isolated Duroia tree. After she has rearedher first brood of young, her offspring will clear the forest by poisoning rivalplant species, and over time more and moreDuroia trees will grow in the spaceleft. The ants will spread to colonize the new Duroia trees and so on as thestand expands. The whole stand is maintained by the single colony. Devil’sgarden ant colonies have multiple queens, which means the colony and theunique genetic material that is represented in that colony can survive for hun-dreds of years—and potentially indefinitely. Researchers have found coloniestending Duroia stands that are over 800 years old, and there are others thatcould be much older.

Since this is such a beneficial mutualism to have evolved, why do Duroiastands not dominate the whole rainforest? There is no limit to the size of theant colony. There are many queens, so there is no definitive range that theycan occupy. The answer seems to be that the ants are perhaps too successfulin excluding other plant species from their garden. Duroia trees in devil’sgardens grow so vigorously that they attract many more herbivores eager fora meal than they otherwise might. Such a predominance of one species that isso productive leads to a high rate of herbivory—more than the ants can protectagainst. Once the devil’s garden reaches a certain size, the rate of herbivoryseems to be sufficient to prevent significant spread, although it is not clear ifthis is the whole story. Clearly, though, the adaptation is extremely beneficialto the Duroia tree, the devil’s garden ant, and even the scale insects that arefarmed inside the trees domatia.


It is perhaps fair to say that the devil’s garden ant and those like it have notled to highly innovative breakthroughs in human invention. But the formicacid that they produce when under attack does have a use for the people wholive in the forest. Locals will put their hands on certain ants’ nests to elicit adefense response from the colony inside. Before long, hundreds, if not thou-sands, of ants swarm out to defend their home, squirting formic acid on theintruder. Once the ants have been brushed off the hands and arms, the person


who incited the attack will be well covered in formic acid, which will be used torub on the skin and act as a strong mosquito repellant—a handy trick in areaswhere malaria is prevalent.

ELECTRICITY

There is little doubt that one of the most significant human advances has beento harness electrical energy. Nearly everything in our lives makes use of theenergy held within electrical currents. Even our bodies are similarly reliant onelectricity. Through our nerves, electric currents control our movements andform our memories. Other animals have evolved to use electricity to communi-cate with each other or as a weapon. Some have even evolved to detect electricalcurrents emitted by their prey, making them highly efficient hunters.

Probably the most well known organism that uses electricity is the electric eel(Electrophorus electricus). This inhabitant of the murky river waters of SouthAmerica is not actually an eel but really a type of knife fish, related to carp and cat-fish. The ‘‘electric’’ part of its name is spot on, though. Most of its body is takenup with the necessary organs to produce and emit electricity. All its other majororgans, from mouth to anus, are crammed in to the front 20 percent of its body.

The remaining 80 percent of the electric eel’s body is made up of three sep-arate organs of modified muscle used for generating electricity. Runningnearly the length of its body on the underside is the Hunter’s organ. Its dorsalside is then divided into two organs: the Main organ toward the head end ofthe body and the Sach’s organ toward the tail end.

The electrical organs are each made up of highly modified, flattened musclecells. These disc-shaped cells, called electrocytes or electroplaques, are stackedone in front of the other and run the length of each organ. Each electrocyte iscapable of producing a weak electric charge—only 0.10 to 0.15 volts. This iscertainly not much and would not be capable of the huge jolts of electricityfor which the electric eel is famous. But the electrocytes do not work inde-pendently. They are lined up in series, which means that the electric chargeflows from one to the other, building in electric potential. There are some5,000 to 6,000 electrocytes stacked in the three electric organs, so workingtogether they can produce some 500 to 650 volts—enough to kill a man. Thesame mechanism is seen in man-made, battery-powered items that requiremore than one standard battery to operate.

So how do these electrocytes work? When not emitting an electrical pulse,the inside of each electrocyte is negatively charged by moving tiny, positivelycharged sodium and potassium ions (atoms that are missing a few electrons)from inside of the cell to the outside. The positive ions are pumped acrossthe cell membrane by specialized ‘‘pump’’ proteins. In this resting state thereis no current flowing from one cell to another. All cells are negatively chargedon the inside and positively charged on the outside. This is like putting bat-teries in the remote control the wrong way—the same poles are next to each


other (positive to positive and negative to negative) so that no current can flowfrom one cell to the next.

To generate an electric pulse, a change must happen in the electrocytes.Electrocytes are like normal muscle cells—they are each attached to a nervecell. Normally the nerve cell would cause a muscle cell to twitch, but in elec-trocytes they have a different effect. Each electrocyte is shaped like a flat discand has two obvious sides (think of the two sides of a frisbee or plate).The nerve is attached to just one of these sides. When a nerve impulse reachesthe electrocyte it causes the protein pumps on that side of the cell to open andstop pumping positive ions out of the cell. This allows the positively chargedions to rush inside the cell. This is like holding water at a dam and then open-ing the sluice gates. Now, the inside of the cell on that side switches from beingnegatively charged to being positively charged.

The neat part is that the other side of the electrocyte—the side that has notbeen stimulated by a nerve—remains unaffected. The ion pumps are still work-ing, so the non-nerve side remains negatively charged inside the cell andpositively charged outside the cell. If we look at the charges in the electrocytenow, on one face of the cell they are negatively charged outside the cell andpositively charged inside. On the opposite face of the cell there is a negativecharge inside the cell and a positive charge outside. From one side of the elec-trocyte to the other, the charges now alternate. This means a current can flowfrom one side of the cell to the other.

The electric current must flow from one electrocyte to the next to generate alarge overall buildup of electricity. To achieve this, the nerves triggering thereaction in each cell must be timed to perfection to switch the polarity of thecell just in time for the electric charge to be passed on. The nerves must stimu-late each subsequent electrocyte a split second after the previous electrocytewas stimulated. After discharging the electrical charge stored in the electro-cytes it does take a short time to ‘‘recharge’’ the cells, although this chargecan be held for a long time. Electric eels have been known to still be able todischarge a jolt of electricity up to nine hours after their death.

Each of the three electric organs produce electricity in the same way,although they differ in their function. The Sach’s organ produces a constant,weak electric field that seems to have a number of functions, includingcommunication. The most important function, though, is as a navigationdevice—very important for a fish with poor eyesight that lives in murky waters.The electric field emitted by the Sach’s organ is distorted by the presence ofobjects in the field. These distortions can be detected by specialized senseorgans called electroreceptors that are sensitive to electrical energy. If eitherprey or a predator is detected, the electric eel can produce a much strongerelectric charge to stun other fish that it wants to eat or flee from. This 650 voltcharge is produced in the Main and Hunter’s organs.

Electric eels are not alone in their ability to generate or detect electricalenergy. Many fish produce an electric charge for communication and


navigation. It is not surprising then that other species of fish have evolved todetect these signals as a way to find prey even where light conditions are poor.The duck-billed platypus, a most unusual creature all around, is one of onlytwo mammals known to detect electrical charges (the other being the echidna).Again, it makes use of this remarkable ability to hunt for food. The use of elec-tricity in this way is certainly unusual in nature, but it allows for fish like theelectric eel to gain a huge advantage over its prey and competitors in anenvironment where vision is poor.


All organisms move charged ions around cell membranes as part of theirnormal cell processes. This is not always done expressly in order to produce astrong electrical current like the electric eel does, but it can have that helpfulside effect. To this end bacteria are already being put to good use for the dualfunction of breaking down chemical waste into less harmful by-products andgenerating useful electricity at the same time.

As discussed in the entry on chemosynthesis, some bacteria can use a wholerange of chemicals as a food source. Certain bacteria get their energy from thiswaste by aerobic respiration. In aerobic respiration, oxygen is needed to mopup electrons released in the process of breaking down the chemical food source.In controlled conditions, these bacteria can be deprived of oxygen and the elec-trons they produce can be harnessed and used to generate an electric current.

Microbial fuel cells are, to date, only found in laboratories and are notcommercially viable, even on a small scale. They are capable of producing onlya few volts, although their designers are hopeful of being able to producemicrobial fuel cells that can be stacked and used in series in the same way asthe electrocytes of electric eels. This could be a prize well worth aiming for.Not only does it offer an inexpensive solution to energy production, but it alsocould be the answer to the problem of disposing of hazardous chemical wasteat the same time.

BIOLUMINESCENCE

In nature, it is unusual for species to evolve any trait that draws too muchattention to themselves. For the most part, if you are easily seen, you are easilyeaten. However, sometimes it is very beneficial to be seen, and some organismscan be very striking indeed if it suits their needs. To these ends we see manydazzling displays of color in peacock tails or brilliant flowers that draw atten-tion to themselves to reproduce. In more extreme cases, though, nature hasmoved beyond simply using color and has evolved the ability to actively pro-duce light.

Human engineering has come up with some fairly crude ways of makinglight, and for the most part we rely on the humble light bulb. Here, electricity


passes through a filament that glows andproduces light. However, as anyone whohas touched a light bulb that has been onfor a while will know, this form of light alsoproduces a lot of heat. In fact, 90 percentof a light bulb’s energy is wasted as heat.Any organism that wanted to produce lightin this way would soon find itself a ready-made barbecue for a passing hungrypredator.

Instead, another method has evolved,and this method doesn’t produce any heatat all. It relies on two chemicals—luciferaseand luciferin—that when they react pro-duce a bright, cool glow. This is becausethe reaction is so efficient that 100 percentof the energy released by the reaction goes

into light production. No wasted energy is released as heat. Both chemicalscan be safely stored by the organism and combined when needed. The produc-tion of cold light by organisms is called bioluminescence.

Bioluminescence is found in many species both on land and in water.On land, it is found in glow-worms (which is actually a beetle, Lampyris), fire-flies, and even in the earthworm. The eerie glow sometimes seen on rottingmatter is caused by light-producing bacteria and fungi. But it is in the oceanwhere bioluminescence is most widespread.

Light from the sun cannot penetrate the sea more than around 650 feet(200 m) below the surface. Below this point, approximately 70 percent of allspecies have some form of bioluminescence, which makes sense with no natu-ral light about. In the sea, bioluminescence is found in species of all sizes.Single-celled plankton called dinoflagellates can produce a light that can beseen from space when they gather in a large enough bloom. Certain fish (suchas the angler fish) and jellyfish (the angler jellyfish) can produce light withwhich to lure prey to their waiting mouth. Even the largest squid in the oceancan produce light. Each of these animals puts their light to their own use—fordefense, hunting, mating, and even to disappear completely from view.

Because deep under water there is very little light, many deep-sea organismshave very poor eyesight. Indeed, what little eyesight they have is restricted toseeing blue light because red light cannot penetrate far in water. One familyof deep-sea fish, however, has evolved a neat trick to exploit this. Species ofthe Loosejaw dragonfish family (the Malacosteidae) can see red light. To makethe most of their keen eyes, they have evolved the ability to produce red lightfrom an organ beneath their eyes. They quite literally have a couple of torchesbelow their eyes with which they can penetrate the gloom of the murky deepocean and pick out tasty morsels. Because this torchlight is red, which other


A species of loosejaw dragonfish, Pachysto-mias microdon. The tear-shaped organ belowits eye (the photophore) emits a red lightwhich illuminates potential prey. The drag-onfish is one of the few fish species that cansee red light, allowing it to hunt with stealth.[Dante Fenolio / Photo Researchers, Inc.]

ocean-bound organisms cannot see, potential prey are not alerted to the loose-jaw’s presence. Nor, indeed, are potential predators of the loosejaw drawn toits torches, making these fish the perfect stealth-attacker.

There are times, though, when species use light to be seen. Most people areprobably familiar with the light that can be produced by fireflies in controlledflashes. There are several species of firefly, nearly all of which use flashinglights to attract potential mates. To avoid confusion, each species has a par-ticular pattern of flashing light so it attracts members of the same species.However, in one instance this species-specific light display has been exploitedto a deadly end. Females of the species Photurismimic the flashing pattern pro-duced by females of the species Photinus. Photinus males are fooled by thistrickery and are drawn to the mimicking Photuris females. Instead of finding awilling mate, these unwitting males encounter a hungry femme fatale and arequickly devoured.

Interestingly enough, the story doesn’t end there. Recently, scientistsdiscovered that the femme fatale fireflies gain an additional benefit from eatingthe Photinus males. In eating the males of a different species they absorb adefensive poison called lucibufagin, which they are unable to make themselves.Fireflies that have this poison repel the spider predators that feed onfireflies—in particular, Phidippus jumping spiders. So not only do thesefemme-fatale fireflies get a tasty snack, but they also gain valuable protectionfrom predators.

Perhaps the most thorough use of light is found back in the ocean. All squidare capable of producing light. Certain species, though, like the large squidTaningia danae, have taken it to the extreme and exploit light production inthree separate ways. Squid have light emitting organs (called photophores)located all over their body. On the main trunk of the body the large squidcan produce a light that varies in color depending where they are in the sea.Much like a chameleon effect, the large squid can produce a light that causesit to blend in with its surroundings, protecting it from predators and remaininghidden from unwary prey.

Safely obscured from view, large squid can hunt for their own prey, and theyeven use their light producing powers to help them do that. Photophores onthe end of their arms can deliver a bright flash that can both blind its preyand allow the squid to judge the distance to its now bewildered victim beforeit starts its final assault. This is particularly important in the dark deep oceanwhere the inability to see prey can give it the chance it needs to escape.

When it comes to finding a mate, the large squid again uses its incredibleability to produce light to assist it in its goal. The changing colors of the largesquid are used in a courtship display to attract a potential mate. It seems thatthe complexity of the display is what makes a suitor particularly attractive,although this behavior has not been well studied and there is still much tolearn about these fascinating creatures and their amazing ability to produceand use light.



We know that all man-made devices for producing light are very inefficient.Consequently, engineers are keen to replicate the perfectly efficient biolumi-nescence seen in nature. However, it has proved tricky to create a light bulbthat uses the luciferase and luciferin reaction because a constant supplyof these chemicals is needed to produce a continuous light. In nature, biolumi-nescent organisms can make more, but that is not possible in man-madedevices.

Luciferase and luciferin have been used in glow sticks that can be ‘‘cracked’’to break a connection between two chambers, allowing the chemicals to mixand produce a bright, if short-lived, light. Perhaps more interestingly, though,bioluminescence is being developed in the field of medicine. Bioluminescencehas been used in gene and stem-cell research to show where and how certaingenes work in the body and how they work differently to cause certain diseases.A gene that codes for bioluminescence is inserted next to the gene that is beingstudied. When the gene being studied is activated, there is a characteristicbioluminescent glow to signify that the study gene is working. This is used inboth in vitro and in vivo gene research. It is thought that this way of targetingcertain genes and their products could be a great step forward in the treatmentof cancer.


2

SURVIVING THE ELEMENTS

SURVIVING THE ELEMENTS—HUMAN INVENTION

Perhaps surprisingly for an animal that has colonized every land mass on earth,humans are not well adapted to the extreme environmental conditions thatthey encounter. Naked and exposed, humans suffer from heat, cold, high andlow pressure, drought, lack of oxygen, and radiation. The human body doeshave some ability to become acclimatized to extreme conditions, though.At high altitude, for example, muscle cells produce more mitochondria, andblood cells produce more hemoglobin in order to compensate for the lowerconcentrations of oxygen in the air. And yet, despite this adaptability of thebody, humans would die out from many of the places they currently live if itwere not for the various inventions they have created to allow them to survive.

Human ancestors left Africa some 1 million years ago to colonize thewarmer climates of Eurasia, where no particular inventions would have beenneeded for survival. After that initial migration, there was little human coloni-zation until 100,000 to 50,000 years ago, a period that corresponds with a hugeproliferation in human innovation. At this time there was a great increase intool production and use. It is thought that this Great Leap Forward (to usethe phrase coined by evolutionary biologist Jared Diamond) was triggered bya significant evolutionary event in humans that led to greater capacity forthought and problem solving. This proliferation in the use of tools would haveallowed early humans to make use of the furs and skins of animals to make pro-tective clothing that, in turn, allowed humans to venture into more extremehabitats.

It is likely that since the first human evolved from an ape-like ancestor,humans have been using natural features as shelters. Today, gorillas and

chimpanzees build nests on the ground or in trees to sleep in, so it is notimpossible that early humans used vegetation in a similar way to gain someshelter during the night. We do know, though, that humans were using cavesfor shelter 50,000 years ago at the time of the Great Leap Forward. Thesenatural shelters would have offered excellent protection from the rain, fromcold at night and in winter, and from the extreme heat and radiation of thesun in the middle of the day. At the same time, humans would have had goodfire-starting skills that could warm the caves and provide further protectionfrom the cold.

Caves, of course, would not have been the only shelters used by humans asthey migrated across the continents. Cutting tools would have allowed humansto cut wood to the appropriate size to build a variety of shelters. As we knowfrom indigenous peoples alive today, a range of frames can be built andcovered either with vegetation and mud or with skins from animals. Such shel-ters could be made permanent or temporary according to the need at the time.

As with many inventions, the use of natural materials allowed humans toadapt well to the challenges they faced. With clothing made from furs andskins, and shelters built from wood, stone, and even snow, human populationscould colonize and survive in more or less any environment on the earth.It wasn’t until around 100 years ago, though, that there were even greater leapsforward.

Perhaps the most extreme land environment on earth is the Antarctic. Sincethe early 1900s humans have pitted their strength, stamina, and fortitudeagainst this freezing, dry habitat. The clothing worn by these early explorerswere heavy and designed to keep the wearer warm and shielded from the hugewinds that blow through the frozen desert. Again, they were made from animalskins and furs, but they had one major drawback. The clothing was not breath-able, which meant that sweat could not dissipate. During periods of intenseexertion the men (explorers would have always been men at this time) wouldsweat, which would soak their clothing. In periods of less activity, the sweat-soaked clothes would draw all-important heat away from the wearer, causinghim to get colder and colder.

Learning from the lessons of these first Antarctic explorers, modern cold-weather clothing relies on man-made fabrics and a system of layering. Thebase layer close to the skin is thin, soft, and made from a water-repelling(hydrophobic) synthetic material that does not absorb water, therefore movingit away from the body. Above the base layer modern explorers wear insulatinglayers, which can be removed or added depending on the conditions. A typicalinsulating layer is made from a polypropylene fleece, a versatile plastic polymerthat can be woven into a thick insulating layer and even treated to be water-repelling. The outer layer gives mainly protection from the wind. It does nothave to be waterproof because no rain falls in the Antarctic. In fact, by notbeing fully waterproof, the clothing can breathe and allow perspiration toescape. There will be some insulation from this layer, especially around the


neck and cuffs, from synthetic fibers or natural ones. Even today, though,arguably the best insulating material is the down from birds, such as theeider duck.

Even with these modern clothes, traveling to the Antarctic still remains ahuge challenge to humans. And it is not just the earth’s poles where tempera-tures can drop to life-threatening temperatures. At the highest points on earththe freezing temperatures can still be extremely dangerous. Furthermore, at thataltitude there is less oxygen in the air, which begins to starve muscles of oxygenand makes work difficult. Beyond 23,000 feet (7,000 m) above sea level, the lowlevels of oxygen indirectly lead to serious brain conditions that can cause death.The body’s response to low levels of oxygen is to send more and more oxygen-carrying blood to the brain. Unfortunately, this has the effect of causing thebrain to swell, physically damaging it. This is why altitudes above 23,000 feet(7,000 m) are known as the death zone. The human body can only survive a lim-ited time here before it must turn back or die.

To counteract the effects of the death zone, mountaineers carry with themindependent supplies of oxygen to avoid brain swelling. In fact, these oxygencanisters are filled with a normal mix of some 21 percent oxygen and 79 percentnitrogen—the same composition as the air we normally breathe. It is the same,fairly simple technology that is used to exploit one of the most inhospitableenvironments on earth for humans—underwater. Although the mix of air andthe design of regulators that control the flow of air to a diver have changedover the years, air tanks for scuba divers have remained more or less the samesince invented by Jacques Cousteau and Emile Gagnan.

The invention of ‘‘portable air’’ has been key to humans’ ability to travel toplaces where they would otherwise be unable to survive. However, the canis-ters carried by underwater divers and mountaineers have a very limited sup-ply—after a few hours the explorer must return to the surface or to loweraltitudes unless he or she can carry a huge number of spare canisters. However,there are some artificial air supplies that last much longer and have allowedhumans to conquer perhaps the most inhospitable environment of all—space.

Rather than compressing air into canisters (which is still used to supply acertain amount of air), space stations are fitted with devices that have oxygenstored chemically. Simple chemicals like potassium chlorate (KClO3) andsodium chlorate (NaClO3) contain oxygen (the O3 part of their chemical for-mula). This oxygen is not bound particularly strongly in these chemicals andwith a little heat it is readily released as a gas (leaving common salt). Thesechemical oxygen stores are extremely efficient ways of storing a lot of oxygenin little space. Weight for weight a chemical oxygen canister is able to supply10 to 20 times the oxygen than a regular compressed air canister. A chemicaloxygen canister contains a sodium chlorate pellet and an igniter to heat it suf-ficiently to release the oxygen. Such devices are used in space stations, air-planes, and submarines. Although, as they occasionally have a tendency tocause fires (because of the need for a heat source and due to the fact that they

SURVIVING THE ELEMENTS 27

release oxygen, a flammable gas), they tend only to be used as emergencybackup supplies.

Space travel not only presents humans with the problem of no oxygen, butalso of radiation. The high energies held within certain wavelengths of theelectromagnetic spectrum and the high energies held within radioactive par-ticles—both of which are encountered in space—cause physical damage tohuman cells and organs. The earth’s atmosphere offers some protectionagainst these dangers, but out in space no such natural protection exists.On spacecraft, metals are used to offer some protection from radiation, suchas aluminum. This has a similar effect to lead-lined suits used to protect wear-ers from radiation leaks on earth. These metals do not offer complete protec-tion, however, and innovative solutions are being explored for long-distancespace exploration such as a possible journey to Mars. Exotic solutions such aselectrostatic fields and liquid hydrogen shells are among the suggestions beingconsidered.

On earth, though, perhaps some of the simpler designs are the ones thathave been the most successful and the most useful to us in our daily lives.A particularly hot day in summer can submit us to dangerous levels of ultravio-let (UV) radiation that can increase the risk of cancer. Sunglasses and sun-screen that contain UV filters can reduce the risk by blocking the light wavesbefore they can penetrate our skin and damage our cells. Within sunscreen,two basic types of UV filter can be used. Organic (carbon-containing) chemi-cals directly absorb UV. Inorganic chemicals (such as zinc oxide) tend moreto reflect the UV light away from the skin.

Through its remarkable ability for innovation, the human species has beenable to exploit all the habitats on the planet. However, some extreme habitatsexist where even the most modern technology cannot keep humans aliveindefinitely. Although no one organism is more successful that humans in thebreadth of habitats it can survive in, there are many species out there that cansurvive indefinitely in the places where humans can only venture for a shortperiod. Some of these species can even survive in space.

THERMOPHILIC BACTERIA—SURVIVING EXTREME HEAT

Survival at very high temperatures is tough. Humans, like all mammals, areable control their body temperature, but these controls are limited and at cer-tain temperatures our bodies will suffer and die. Above about 110°F (45°C) ourmuscles will become rigid and immobile, and the millions of proteins thatdrive the reactions inside our cells (enzymes) will break down. Because of ourown experience and the experience of most animals and plants, it was thoughtthat no life could survive indefinitely at temperatures much above 120°F(50°C). True, some species had been observed to enter protective states at veryhigh temperatures, but none were seen to thrive and reproduce at such hightemperatures.


That is, until the late 1960s when sci-entist Thomas Brock discovered a newspecies of bacteria living in the hotsprings of Yellowstone National Park.These springs are made from hot waterbubbling through the earth’s crust, hav-ing been heated by the molten magma ofthe earth’s core. It is not surprising, then,that temperatures in these springs reachclose to boiling point: nearly 212°F(100°C). Yet within these springs bacteriawere found to thrive. The first bacteria tobe discovered by Brock was called Ther-mus aquaticus, referring to the hot waterin which the bacterium was found. Butsince then around 50 thermophilic(meaning ‘‘heat loving’’) bacteria havebeen found either in the hot springs onthe surface of the planet or in the hydro-thermal vents found deep within theocean.

Until they were discovered, such bac-teria were not expected to exist. Above120°F (50°C) a number of things happen.The cell membranes that keep an organ-ism’s cells together will break down. DNA will begin to unravel.The proteins and enzymes that drive the cellular reactions that are essentialfor life lose their shape and become useless. In large, multicellular organismslike humans the body can respond up to a point to protect its cells, DNA,and proteins. But if large animals can’t survive in near-boiling temperatures,what chance does a single-celled bacterium have?

Thermophilic bacteria have evolved a number of neat adaptations to helpsolve the problem. First, their cell membranes are not like the cell membranesof animals. They have a number of molecular ‘‘add-ons’’ that keeps the mem-brane very rigid and resistant to temperature. There are various add-ons thathelp, but the most important are molecules of fat that are combined with amolecule of ether (the same compound that, in gas form, was used as an earlyanesthetic). The extra fat and ether molecules act as a scaffold that supportsthe cell membrane and give it extra strength. Thus, the bacteria can stay inone piece, but there is still the problem of protecting the DNA, proteins, andenzymes within the cell that keep the bacteria alive.

DNA contains all the genes that control the lives of all living organisms.It is made up of two strands, which are tightly twisted together like a rope.DNA must stay coiled up; otherwise it becomes easily damaged. At high


A computer simulation of DNA-polymerasein the process of replicating DNA (the helicalmolecule in the center). Bacteria like Thermusaquaticus have very robust DNA-polymeraseenzymes that do not break down at high tem-peratures, allowing them to survive in condi-tions of up to 250°F. Resistant DNA-polymerase enzymes from these bacteria areused in genetic and forensic research.[Laguna Design / Photo Researchers, Inc.]

temperatures, though, this coiling breaks down and the two strands fall apart,which shortly leads to an organism’s death, particularly in a single-celledorganism like a bacterium. Thermophilic bacteria such as Thermus aquaticushave a unique ability to coil up their DNA even tighter than usual by twistingit back on itself repeatedly. This is called supercoiling. It does this with a typeof enzyme that is not found in any other living organism. By coiling up verytight, the bacteria DNA can combat the damaging effect of extreme heat.

Finally, thermophilic bacteria have very rigid and robust cell proteins andenzymes. These are complex biological molecules that control the reactionsthat go on inside all living organisms’ cells. They are intricately folded mole-cules, and their shape is the key to their success. At high temperature, proteinsand enzymes lose their shape, making them useless—a bit like a shapeless,melted key trying to unlock a door. All enzymes hold their shape through aseries of linking molecular bonds that act as supporting struts. In organismsthat live in cooler environments these bonds are very weak and easily breakdown. They are much stronger in thermophilic bacteria, however, allowingthe molecules to keep their shape.

Thermophilic bacteria all belong to a group of bacteria called the archae-bacteria, very ancient bacteria that have been on this earth for as long as lifehas been. It is thought that they first evolved this ability to thrive and repro-duce in extreme high temperatures when the earth’s climate was very hot andvery steamy. It seems that some of the species maintained this ability to survivein near-boiling conditions and used it to exploit environments like hot springsand hydrothermal vents. Being rather unique, they can exploit these habitatsfree from the competition of other bacteria.

Species like Thermus aquaticus found in hot springs tend to thrive around160 to 175°F (70 to 80°C). Hydrothermal vents in the deep ocean tend to behotter, and species are found there are capable of withstanding temperaturesof more than 212°F (100°C). (Because the water in the deep ocean is undersuch high pressure, it doesn’t boil.) The bacterium Pyrolobus fumarii can stillreproduce at 235°F (113°C). The current record holder is a very recentlydiscovered species—simply called Strain 121—that can reproduce at anincredible 121°C or 250°F!


During growth and reproduction all organisms need to replicate cells. All ofus started life as a single cell that has been replicated many times during ourlives. One of the key steps in the process of cell replication is the replicationof the DNA held within it. This in itself is a fairly complicated business, butin essence it involves pulling the two strands of DNA apart and replicatingthem both to produce two ‘‘daughter’’ copies from the original. The enzymethat controls this DNA replication process is called DNA polymerase.

DNA polymerase is found in Thermus aquaticus like any other organism,although, of course, the enzyme in T. aquaticus is resistant to extreme heat.


This feature of its DNA polymerase has been exploited to allow for one of themost significant techniques used in genetics today—the polymerase chainreaction. Researchers and forensic scientists who want to work with DNA forwhatever reason need a lot of it to carry out their tests. Rather than get a hugesample of DNA from the subject (which may not even be possible in policeforensic work), a small sample of DNA is taken and replicated over and overagain, making use of the DNA polymerase enzyme.

The process of replication by the polymerase chain reaction can be carriedout automatically by machines in just a few hours. But it requires high temper-atures of around 175–195°F (80–90°C) to work. DNA polymerase taken fromany other organism would just not work at these temperatures, but the DNApolymerase from T. aquaticus can. As a result, geneticists and forensic scientistscan get the amounts of DNA they need to carry out their work.

BLOOD ANTIFREEZE—SURVIVING EXTREME COLD

All organisms, from the humblest single-celled bacteria to the largestmammal, need some fluid or other to carry essential nutrients around theirbody to stay alive. In animals like humans, this life-critical fluid is blood.Blood carries nutrients to organs, and it helps regulate body temperature.Without it, animals die. Blood can be lost if the animal sustains a seriousinjury, causing it to bleed to death, but that is not the only way. It is muchless common, but the same effects of blood loss can occur when an animal’sblood freezes, which is what happens when its body temperature falls tobelow 29.3°F (−1.5°C).

Because of these serious consequences, most animals avoid very cold tem-peratures. One group of fish, however, calls these environments home. TheNotothenoid fish are native to the freezing waters of the Antarctic and makeup over 95 percent of the creatures that live there. Here the seas are as coolas 28.6°F (−1.9°C), only fractionally warmer than the freezing temperature ofsalt water: 28.4°F (−2.0°C). Normally, this would freeze the blood of any fishstraying into these waters. The Notothenoids, however, have a secret weapon.They have a biological antifreeze in their blood that stops their bodies fromfreezing.

The Notothenoids can cope with very tiny ice crystals forming in theirbodies. Their secret is to stop these tiny ice crystals from growing bigger,and having a damaging effect, by producing a group of proteins called anti-freeze proteins. These antifreeze proteins bind, at a molecular level, to thetiny ice crystals in the body and prevent them from growing bigger. Thisway, the fish can lower the threshold temperature at which their bloodfreezes to 27.5°F (−2.5°C). This enables them to cope perfectly well in thenear-freezing Antarctic waters.

It is thought that the Notothenoid antifreeze adaptation evolved some5 million to 14 million years ago. It has been such a successful adaptation that


the Antarctic waters are dominated by these fish, not because they have aggres-sively kept out other species, but simply because they are the only fish that cansurvive there. Since the early Notothenoids invaded the Antarctic, around120 species have evolved, each species exploiting a different niche in thisfreezing ecosystem.

The evolution of the antifreeze proteins was a mystery that scientists haveonly recently understood. Ever since antifreeze proteins were first recordedin the 1970s, it has been assumed that they were produced by the fish’s liver,which is where most blood proteins are synthesized. It was only in 2006that scientists discovered that the proteins are made in the pancreas andstomach and are secreted into the intestines, where they are absorbed intothe blood.

It used to be thought that antifreeze proteins evolved from a group of pro-teins whose use was to prevent the gut from suffering from very cold condi-tions. This appears not to be the case, though. It is now believed that theability to make antifreeze proteins evolved from scratch from a mutation inthe so-called ‘‘junk’’ DNA of the fish. Junk DNA is apparently useless sec-tions of DNA found between the genes that code for the essential biologicalmolecules that make up the body of an animal. Scientists did not believe thatjunk DNA could evolve in this way, so there are still some questions toanswer before the mystery of how this adaptation has evolved is finallysolved.

It is fair to say that the ability to make antifreeze proteins has been a remark-able adaptation. Free from competition of less-hardy fish, the Notothenoidshave evolved to colonize every part of the ocean. The Threadfin Pithead,Aethotaxis mitopteryx, can be found some 2000 feet below the surface. At theother end of the extreme, the Bald Rock Cod, Pagothenia borchgrevinki, can befound lurking right under the ice that forms over the surface of the sea, andeven burrowing right through the ice itself. In fact, the Bald Rock Cod is sowell adapted to these freezing climes that it will die in waters warmer than just42.8°F (6°C). This is the lowest upper threshold temperature known to kill ananimal. The Notothenoids truly have conquered the Antarctic seas thanks tothis one adaptation.


There are already a number of commercial uses for Notothenoid antifreezeproteins, which is not surprising considering that they are around 300 timesmore effective than conventional chemical antifreezes of the same concentra-tion. By inserting the antifreeze protein genes in yeast and bacteria, the pro-teins can be grown and harvested on a large scale. It is hoped that thistechnique can be adapted and that the genes can be inserted into plants toengineer cold-resistant crops that can resist potentially fatal frosts.

Antifreeze proteins harvested from bacteria already have industrial applica-tions, and scientists are exploring their use for cold-storing foods that become


inedible when frozen. As an extension of this, the fish proteins may find a use inthe field of cryogenic storage of body parts. The use will most likely be fortransport and storage of organs for transplant rather than for multimillionaireswho want their bodies frozen before death and reanimated some time in thefuture!

MAMMAL FUR—SURVIVING EXTREME COLD

As humans, we are well aware of the risksof extreme cold. We are very vulnerable iftemperatures drop too low, as we lack a sub-stantive layers of insulation. Being warm-blooded animals, we can regulate ourinternal body temperature reasonably well,but the system is far from perfect. Humansevolved in the tropics and so are suited towarmer climates rather than cooler ones.Naked, a human will start to feel cold as tem-peratures drop below 77°F (25°C). At 54°F(12°C) humans lose manual dexterity. (Trytying your shoelaces if your hands are coldand you will know how difficult this can be.)At 46°F (8°C), we lose touch sensitivity.

As temperatures continue to drop, the human body will struggle to keep itsinternal temperature constant. Blood flow will be reduced to the extremities toconserve heat within the bulk of the body, which is why frostbite affects thefingers and toes. As temperatures drop yet further our internal body tempera-ture will drop by a few degrees and the effects of hypothermia will kick in.The affected person will become sluggish and eventually die because the bodytemperature is too low for metabolism to take place.

To get around these problems and to exploit colder climates, humans havetaken to using the insulation of other animals. Humans have worn furs forthousands of years to keep warm for the very good reason that fur is anexcellent insulator of heat.

Mammals are the only animals that are covered in hair. Hair itself is madefrom a long chain of dead cells filled with the strong protein keratin. It growsfrom a deep pit in the skin called a hair follicle. Cells grow at the base of thehair within the follicle and are gradually pushed upward as other cells growbehind them. This is how hair grows. This growing point within the follicleis weak, and hairs can be pulled out with relative ease. Hair itself, though, isvery strong thanks to its structure of keratin. A single human hair can supporta weight of 6.6 pounds (3 kg).

Hair follicles are supported by a sebaceous gland that secretes cells filled witha fatty oil that coats the hair to keep it supple, strong, and, to some extent,


Scanning electron micrograph of the fur ofthe polar bear, Ursus maritimus. The hollowhairs trap air which help insulate the bear’sbody. The hair is also oily to repel water.[Andrew Syred / Photo Researchers, Inc.]

waterproof. Each hair is connected to an arrector pili muscle, which can be con-tracted to cause the hair to stand on end. This is a very important feature ofthe hairs that make up an animal’s fur. When the hairs are erect, the fur as awhole becomes ‘‘fluffed up.’’ Air becomes trapped in the fur, which helps insu-late the animal’s body. Humans, although essentially hairless, still show thisadaptation.When we are cold we get ‘‘goose flesh,’’ which is caused by the arrec-tormuscles pulling to make our hairs stand on end. This adaptation is controlledby the hormone epinephrin (adrenalin), which explains why we get ‘‘goose flesh’’when we are scared or nervous and our bodies start to produce epinephrin.

The simple process of trapping air between a dense layer of hair has proved tobe a very successful adaptation. Mammals are able to withstand great extremes ofcold thanks to their fur and a layer of blubber. One of the most successful ani-mals in this regard is the polar bear, which has a thick layer of fur that allows itto live quite comfortably in temperatures as low as −34°F (−36°C) and still main-tain a steady internal body temperature of 98°F (37°C). Its fur is made from twolayers: a layer of long, tough hairs some 5–15 cm long overlays a layer of shorter,softer hairs. The softer fur traps air between the hairs, and the longer fur stopsthe air from dissipating. The softer fur is white and much like the hair on anyother animal. The outer fur, however, is transparent and hollow—the normalcore of hair is missing, leaving only the outer sheath.

It is this hollow hair that has led to a number of wild speculations about thepolar-bear’s ability to keep warm, almost none of which are true. It has beensuggested that the hollow, transparent hair might work like a fiber optic cable.Fiber optics are thin, transparent tubes of plastic that refract (bend) light insidethem in such a way that it runs down the optic like electricity flows through awire. It has been suggested that the transparent hair of a polar bear works inthe same way and funnels light down the hair directly to the skin, which wouldbe warmed up. This is an interesting idea but just not true. Polar bear fur iseffective at keeping heat in, but it is not as high-tech as some people like tothink. It is much more likely that hollow fur traps air inside it, giving itfurther insulating properties.

In addition to fulfilling its primary role of insulation, fur has other impor-tant secondary functions. Fur can be colored by the molecule melaninproduced within the growing cells at the base of a strand of hair. Melanin isactually a whole class of colored molecules of which there are two main types:eumelanin is the dark pigment that is dominant in brown and black hairs,phaeomelanin is a lighter pigment found in blond and red hair. Hairs aretherefore restricted to a palate of reds, yellows, browns, and blacks. Mammalfurs can come in a wide variety of colors and patterns. Each pelt is perfectlyadapted to give its owner a competitive edge, whether it assists with communi-cation, camouflage, or as a warning signal.

In some animals, fur even plays a role in getting rid of dangerous poisons.The pen-tailed tree shrews of the Malaysian rainforests feed on the giant flow-ers of the bertam palm. Thanks to the heat of the rainforest, the sugary nectar


of these flowers ferments with naturally occurring yeasts and produces alcohol,sometimes in concentrations of up to 4 percent alcohol by volume, about thesame as a normal beer. The tiny shrews can consume this without even theslightest sign of drunkenness because their bodies metabolize alcohol quicklyand produce a metabolic by-product called ethyl glucuronide. Thiswaste product is safely excreted in the cells that produce the animal’s fur.Thanks to this ingenious adaptation, tree shrews have access to a nutritiousfood source that many other animals must avoid.


With less and less fur being used for human clothing, there is a great deal ofeffort being put into finding synthetic materials that match the insulatingproperties of animal fur. Synthetic materials are coming close to the effective-ness of furs by mimicking the structures. Hollow fibers made from polyesterhelp trap air like polar bear fur. Some artificial furs are layered with a fluffylayer of fibers laid over the top of thinner fibers—again, just like a polar bear.

Even the fur of the pen-tailed shrew is being studied, although not for itsinsulating properties. Instead, research is being undertaken to understandhow the tree-shrew’s metabolism works to nullify alcohol by converting it toethyl glucuronide and excreting it in hair. This could lead to an importantdrug to help treat alcohol addiction.

MANGROVES—SURVIVING EXTREME SALT

Mangrove swamps are unique habitats found on the coasts of the tropics andsubtropics. The waterlogged soil is highly saline (salty) and very low in oxygen,making it one of the more harsh environments for plants to grow. The swampstend to be dominated by mangrove trees of the family Rhizophoraceae, althoughother species can survive there. These hardy trees have evolved several adapta-tions to cope with such a poor environment, allowing them to thrive whereother species simply cannot survive.

With high temperatures causing evaporation from tropical coasts, sea waterhere has very high concentrations of salt, which causes two problems for plants.The first problem involves the plants’ getting water, which may sound strangebecause plants growing on the coast are constantly submerged in water. In nor-mal conditions, water will move from the surrounding soil into a plant’s rootcells by a process called osmosis. During osmosis, water will move across a cellmembrane from a place where salts are very diluted to an area where salts arevery concentrated. In normal circumstances, the salt content of water in the soilis very diluted, which means it will pass into the more concentrated fluid withinthe root’s cells. In mangrove swamps, the reverse happens. The sea water is sosalty that it is more concentrated than the fluid in a plant’s root cells. Watertherefore would flow out of the root, causing the plant to dry up.


The highly specialized roots of mangrove plants. Aerial roots allow the plants to drawup oxygen in oxygen-poor waterlogged soils. [F. Stuart Westmorland / PhotoResearchers, Inc.]

The second problem is that too much salt can be toxic to a plant. Salt ismade up of sodium and chlorine and will split into these constituent elementswhen it dissolves in water. If this water is absorbed by the plant, the chlorinewill destroy the chlorophyll in a plant’s leaves, depriving it of its ability toderive useful energy from photosynthesis. Salt-afflicted plants often show acharacteristic ‘‘scorched’’ look on their leaves where the normally greenchlorophyll has been broken down. What makes matters worse on tropicalcoasts is that tides and variable weather conditions can lead to variable levelsof salt in the sea water, making it harder for a plant to adapt to the conditions.

One solution to the problem of getting water is to tolerate salt and to maketheir root sapmore salty than the surrounding water by actively absorbing salts.This means that water will be drawn in from the surrounding sea water ratherthan it being lost from the roots. Of course, this means that the plants must beprotected from the high salt levels that they take on board. Species that adoptthis method for acquiring water must then secrete the salt that they have takenup. Species like Avicennia, Acanthus, and Aegiceras have specialized salt glandson their leaves that secrete salt. Sodium and chlorine salts are actively trans-ported to these salt glands where the salt is excreted.Water is conserved thanksto a waxy, waterproof coating over the leaves that prevents water from escap-ing. Salt crystals deposited on the leaves are quickly blown away by the windor rain.

Other mangrove species, like Bruguiera, Lumnizera, and Rhizophora, getwater thanks to specially adapted root cells that pump in water and activelyfilter out the salt. This process is energetically expensive, but it does preventvery high levels of salt from building up the sap. This is not a perfect solution,though, and they must still excrete salt from their leaves as well. Another wayin which toxic salts can be excreted is for the plant to transport them to oldleaves and stems. These are no longer essential for photosynthesis and can beused as a salt repository. Soon the leaves will fall off, taking the salt with them.

These adaptations allow mangrove trees to survive in conditions that wouldbe too salty for many other forms of life to survive, but even they cannot sur-vive extreme salt conditions for long. Mangrove trees must ‘‘flush’’ their cellsfairly regularly with fresh water that flows from the rivers and streams thatmeet the coast. This helps remove salt in the plants’ cells and provide themwith much needed salt-free water.

Not only must mangrove trees cope with salty conditions, but they are facedwith the challenge of growing in very oxygen-poor soils. The mud into whichtheir roots reach is heavily waterlogged—being on the coast—which meansthere is very little oxygen present. In other plants, oxygen is drawn up by theroot cells as well as water. This is possible because most soils will hold waterbut also have pockets of air within them. This is why gardeners and grounds-keepers are so keen to aerate their soils.

Mangroves still absorb their essential oxygen through their roots, but theyhave adapted a unique way of doing it. Given that there is no oxygen to be


had below water, mangrove roots will grow above the water level as well.These roots are called aerial roots. Aerial roots are found in different guises,but the most common type are the pencil-thin roots called pneumatophores(meaning ‘‘air-carrier’’). Mangrove trees can put out as many as 10,000 of thesepneumatophores in order to get enough oxygen to respire. All aerial roots arecovered with tiny pores called lenticels that only allow air to pass through;water and salts are kept out. Once air has been taken in through the lenticelsit passes into one of the large air spaces within the aerial root called aeren-chyma. These air spaces are used to transport air to other parts of the plant,but they also act as a reservoir of air for when even the aerial roots aresubmerged at high tide.

The salt conditions of tropical coasts represent a very harsh environmentin which to exist. Mangrove trees are highly specialized to be able to livethere, and even these remarkable plants are on the brink of survival. Thereare very few plants that have adapted to this way of life, which means thatmangrove swamps are dominated by only a few species. The reward for thesetrees, though, is that this environment is their own. Having overcome suchinhospitable conditions they can flourish free from competition from otherspecies, making them, evolutionarily speaking, a very successful group ofplants.


The ability for mangrove species to survive in highly saline conditions hasimportant implications for developing the crops of the future. Intensive farm-ing relies on the application of chemical fertilizers to the soil. Over time, thesefarming practices can increase the levels of salt and reduce soil fertility, makingit hard to grow conventional crops. Biotechnology companies are alreadyexploring whether it is possible to engineer crops with the ability to cope withsalty soils by inserting genes from mangrove trees.

LUNGFISH—SURVIVING WITHOUT OXYGEN

It is believed that life began in the earth’searly oceans. Over time life moved fromwater onto land. This may sound like afairly straightforward progression, but it isnot. Evolutionarily speaking, the movefrom water to land represents a huge leap.Bathed in water, fish and other aquaticorganisms don’t have to worry about con-serving water. On land, organisms mostcertainly do. What’s more, adaptations formoving in water are next to useless on land,


The African lungfish, Protopterus annectens.This species can use both gills and itsprimitive lungs to gain oxygen. [TomMcHugh / Photo Researchers, Inc.]

and of course breathing on land is a completely different prospect to gettingoxygen under water. To an organism living in water, dry land represents assevere and hostile an environment as it can get.

So how did life move from the seas to land? Surely the need to evolve anentirely different way of life would be too much of a leap. What we mustremember, though, is that evolution works by taking small steps, not big ones.Over time, small changes and adaptations build up to allow water-boundorganisms to break out and colonize what would have represented an inhospi-table desert. Rarely do we see these tiny evolutionary steps take place; we tendjust to see the big differences that are the result of thousands and thousands ofyears of evolution. But there is one group of fish—the lungfish—which still tothis day shows adaptations that would have been hugely significant in the movefrom water to land.

The lungfish are a primitive fish from the class Sarcopterygii. They are asolid-looking fish between 5 and 6.5 feet long (1.5–2 m). They can be foundin Australia, South America, and Africa in freshwater pools that are prone tocycles of flooding and drought. The wet season represents little problem forlungfish, as they can feed freely in their pools and grow in size. The dry sea-son, though, can cause their pools to shrink dramatically. During thesetimes, the lungfish seek refuge within the mud of the drying pool bed.It can burrow up to 3 feet (1 m) down to seek out moisture. Once buried,they will curl up and excrete a thick mucus that covers their body and pre-vents them from drying out. The lungfish will also enter a state of torporwhere its metabolic rate lowers. It can last up to two years in this state ofestervation.

As their name suggests, lungfish have evolved air-breathing lungs to copewith these dry seasons, when the pools in which they live will becomedepleted of oxygen and their gills become useless. When the lungfish burrowinto the mud, they will leave a small hole in their mucus cocoon to allow airto get through so they can breathe. The Australian lungfish use gills tobreathe during the rainy season when their pools are filled and well oxygen-ated. They will switch to lung-breathing only in times of drought. TheAfrican and South American lungfish, however, have lost the ability to getenough oxygen from water using gills alone and depend on lung-breathingall-year round.

The presence of primitive lungs in the lungfish is certainly compelling evi-dence to suggest how organisms might have evolved the necessary adaptationsto colonize land. But there is more to this adaptation than simply being a pairof air sacs capable of gulping down air. Air taken into lungs is not just a mixtureof gases, but will hold a certain amount of moisture. Water in the lungs, eventiny amounts, is not a good thing. As the lungs breathe out they will collapseon themselves. When this happens, on every breath, moisture can cause thesurfaces of the lungs to stick together. To see the principle at work submergea plastic bag in water. When you pull it out you will see that it becomes stuck


to itself because of the binding properties of the water molecules. If this wereto happen to lungs, it would make it impossible, or at least very difficult, tobreathe in again.

To get around this problem, lungfish have evolved an anti-glue (or ‘‘surfa-cant’’) protein that lubricates the lungs and prevents them from collapsingand sticking together. This surfacant protein (actually a mixture ofproteins, fats, and cholesterol) is found in all animals with lungs, includinghumans. Although our lungs have evolved well beyond the primitive air sacsof the lungfish, we share the same adaptation for keeping our lungs fromcollapsing and sticking together. Seeing as they are still found in animalsseparated by some 300 million years of evolution, surfacant proteins areclearly a successful adaptation that have allowed life to flourish on land.


There is little we take from lungfish that has a practical application,although there is currently a great deal of research into understanding the pro-duction of lung surfacants as part of the treatment of diseases like cystic fibro-sis, which causes the production of a very thick mucus in the lungs. Lungfishalso give us a valuable insight into how land-based animals evolved. In additionto the evolution of lungs and their mucus cocoon, lungfish also show otherprimitive adaptations for surviving dry conditions. Their basic body plan mir-rors that of all land-based animals. They have two pairs of fins, which lungfishcan use to walk along the bottom of their pool. These correspond to the frontand hind limbs of terrestrial vertebrates. Lungfish truly are living fossils thatgive us a glimpse 300 million years into the past when animals were leavingthe water to colonize the land.

MELANIN—SURVIVING RADIATION

The energy of the sun is responsiblefor so much of life on earth. It is evenan important source of vitamin D,which is essential for bone health andimmune functions in humans and othermammals. However, the energy fromthe sun can be damaging as well. Ultra-violet (UV) light from the sun can dam-age the DNA within our skin cells aswell as affect our immune system andeyes. UV radiation destroys DNA atthe molecular level, which can causeskin cancer, the most common formbeing melanoma.


A scanning electron micrograph of an eyemelanocyte cell, showing the pigment gran-ules which give the cell color. [SteveGschmeissner / Photo Researchers, Inc.]

There are a number of remarkable adaptations that have evolved toprotect animals against the sun. For example, DNA has a remarkable abilityto repair itself after damage sustained from UV radiation. The first and mostimportant line of defense, however, is melanin, the pigment that gives ourskin color and that blocks out much of the sun’s harmful rays. It is ournatural sunscreen.

There is no doubt of melanin’s ability to protect human skin. Skin cancersare far more common in Caucasians, whose skin is much lighter and lackingin melanin than the skin of African races. But even Caucasian races are ableto produce melanin in response to exposure to sun, offering some protectionagainst UV. Sunlight triggers the production of this pigment from the aminoacid tyrosin by stimulating the enzyme tyrosinase, which controls the conver-sion of one molecule into the other. It is this controlling enzyme that is lackingin albinos, preventing them from making any melanin at all.

There are two common types of the pigment: red melanin (phaeomelanin)and black melanin (eumelanin). Red melanin is more prevalent in fair-skinned people and gives red-haired people their hair color and the reddishfreckles on their skin. Red melanin gives some level of protection againstUV, but nowhere near as much as black melanin, which can block out nearlyall the light falling on it. Black melanin is a dark pigment that is found in aspecial type of cell under the skin called melanocytes (literally meaning‘‘black cells’’). The dark pigment directly blocks the sun’s rays. Nearly all lightand importantly over 99.9 percent of the harmful UV radiation that falls onmelanin is absorbed.

The secret to melanin’s amazing ability to shield our cells from the damag-ing effects of the sun’s rays lies in its molecular structure. Melanin has evolvedto achieve what is known as ultrafast internal conversion of energy, which is aremarkable ability of certain molecules found in nature to rapidly absorb alot of energy and dissipate it very quickly and safely before it can cause anydamage.

There are two important stages in the process of light absorption that givesmelanin its extraordinary protective powers. By absorbing all the UV before itcan hit sensitive cells lying beneath the skin, it takes the brunt of the attackfrom the sun. But anything that absorbs a lot of energy is liable to be badlydamaged itself. Think of what happens when a car is given too much gas andthe engine over-revs. If it is kept up for too long the engine will shake itselfapart. Melanin, however, can go on absorbing the energy from the UV radia-tion over and over again without damage. This is because it can release theenergy as harmless heat before any damage can be done. The whole processof absorbing and releasing energy is extremely quick (as the name ‘‘ultrafastinternal conversion’’ implies). The whole process takes less than one picosec-ond—one million-millionth of a second.

This quick absorption and release of energy from the sun occurs muchquicker than any man-made product—human engineers have got nowhere


close to replicating this remarkable feat. There are several other biologicalmolecules that show this ultrafast internal energy conversion. DNA itselfcan absorb and release energy from UV radiation, for example, which helpsprotect the genetic material from damage should any UV get past themelanin defense.

It is likely that DNA, melanin, and other natural molecules that are involvedin combating the very powerful energy from the sun evolved this lifesavingability to quickly absorb and release energy when life first evolved. WhenDNA first appeared in the primordial soup millions of years ago, its ability towithstand attack from UV radiation would have helped it survive to makethe first formative steps in producing life on this planet. Apart from DNAemerging in the first place, this ability to withstand radiation from the sunmay well have been the first adaptation to evolve on this planet, allowing lifeto thrive.


Man-made sunscreens are effective at filtering between 95 and 97 percent ofthe harmful UV that can cause skin cancer—just short of melanin’s 99.9 per-cent absorption. It is not surprising, therefore, that sunscreen manufacturersare turning to nature to boost the efficacy of their product. Melanin used tobe a prohibitively expensive product to collect. The most common sourcewas cuttlefish ink. (Melanin gives the ink its dark color.) Now, melanin canbe produced on more industrial scales in fermentation tanks and can be usedin the mass-produced sunscreens. Currently, melanin is absorbed onto micro-scopic sponges that can be used in a cream. This technology is still beingdeveloped, but it is hoped that it will succeed in making exposure to the sunsafer than ever before.

PARASITISM—SURVIVING HOST DEFENSES

Animals such as humans must be able to cope with fluctuating environmen-tal conditions and attack from other organisms if they are to survive. Some ani-mals, though, do not have to worry about such conditions. They have evolvedto live in an environment where they can escape from unpredictable environ-mental conditions and where there are few, if any, predators or infectious bac-teria and viruses. These animals have taken the evolutionary step of livinginside other organisms—they are parasites.

Living inside another organism has many benefits, particularly if it iswithin a mammal that regulates its body to near-constant conditions. Foodis easily obtained and there is protection from the harsh outside world. How-ever, parasites do not have it all their own way. Most host organisms are nonetoo keen on having something else living inside them. Parasites cause diseaseand are a drain on the nutrients that the host needs for itself. Consequently,


hosts have evolved elaborate defensesagainst potential parasites, and it is thisattack that the parasite must defend itselfagainst if it is to survive.

Humans are subject to many parasites,but one of the most common is the round-worm, Ascaris lumbricoides. It is thought thataround 1.4 billion people are infected withthis species—some 25 percent of the world’spopulation. Adult worms live inside thesmall intestine after a complex migrationthrough the body. Eggs live in the soil andget into the body by the human hostswallowing infected food. The eggs mustfirst survive the harsh, acidic conditions ofthe human stomach. Thanks to a tough,chitinous outer coating that is ridged to giveextra strength, the eggs will survive to passthrough to the duodenum. Rather thangrowing into adults here, the eggs hatchand the larvae burrow into the muscular gut wall. From here, the larvae arecarried in the blood to the heart and then to the lungs.

The larvae will emerge from the lungs into the lung cavity and either worktheir way up to the throat or will be coughed up. At this point, they are re-swallowed and must survive the acidic gastric juices of the stomach once more.Only larvae that are fully mature at this point will survive. Once again, theypass through the stomach and reach the intestine, where the final molts occurand the larvae develop into fully grown adults. Adult females grow to justunder 1.5 feet (0.5 m) in length, although males are a little smaller.

Once in the intestine, life is good for the giant roundworm. It can feed onfood particles passing through the intestine, and the warm, moist environmentof the gut provides near ideal living conditions. However, there are two thingsthat are not ideal for this intestinal worm.

Being an oxygen-breathing organism, humans have comparatively highlevels of oxygen coursing through their bodies. Oxygen is a corrosive gas,and it does the roundworm no good at all. Without taking action, a round-worm’s body would be gradually corroded by the oxygen, causing death.To counter this potential problem, Ascaris uses a specialized molecule thatmops up the oxygen that is present in the human gut. This is a remarkableadaptation because it allows the worm to create its own ideal environmentin which to live.

The molecule that Ascaris uses to clear away the corrosive oxygen is in factthe same molecule that all oxygen-breathing animals use to store and transportoxygen around the body—hemoglobin. In humans, oxygen binds to


A section through the roundworm, Ascarislumbricoides. The thick cuticle helps theworm to resist the immune response fromthe human host in which it lives. [ScienceSource / Photo Researchers, Inc.]

hemoglobin just tightly enough so that it can be transported through the bodyin blood but not so tightly that it can’t be readily released again for respiration.In Ascaris, however, hemoglobin has evolved to bind to oxygen extremelytightly and not release it at all. In fact, Ascaris hemoglobin ‘‘grabs hold’’ of oxy-gen about 25,000 times more tightly than human hemoglobin, making it aneffective way of detoxifying this poisonous gas.

In addition to having to make this environmental adjustment, Ascaris faces amore direct attack. Humans, like most mammals, have evolved an effectivedefense against parasites. The host immune system can detect a foreign bodylurking in its intestine and will produce protein-digesting enzymes (proteases)to attack it. These protein-digesting enzymes (such as pepsin and trypsin) eataway at the bodies of potential invaders, causing death.

Again, though, Ascaris has a couple of tricks up its sleeve. It has evolved avery specialized, hardened cuticle (skin) that is resistant to these attacks. Thecuticle of Ascaris roundworms is very different from those of related, but free-living (nonparasitic) worms. If you were to look at one under a very powerfulmicroscope you would see that the proteins that make up the cuticle are boundtightly and are wound together in a very strong triple-helix structure, muchlike the thin but tough ropes that climbers use.

A thick skin certainly helps fend off the host’s immune attack, but it wouldbe much better to neutralize the attack at the source. This is precisely whatAscaris does. It can release a substance that binds to the host’s protein-digesting enzymes and render them useless. It is still not clear how theroundworm manages this. The roundworm certainly releases some neutraliz-ing chemicals itself. There is also evidence that the parasite can releaseanother chemical that manipulates the host’s organs, causing them to pro-duce neutralizing chemicals too. It seems that the parasite can use the host’sown body to counteract its own immune defenses! Just as humans havemanipulated their environment to increase their own survival, Ascarishas evolved to create a perfect environment inside a human host in whichto flourish. This is indeed a remarkable adaptation to exploit a novelenvironment.


The amazing ability of Ascaris hemoglobin to bind so tightly to oxygen isbeing exploited by scientists as a potential way to treat cancer. Current cancertreatments are very aggressive forms of treatment. Scientists are thereforeworking on ways in which cancer cells can be killed off by starving them ofoxygen. Like normal cells, cancerous cells need oxygen for respiration, andwithout it they die. Various attempts have been made, but with little successso far. With the relatively recent discovery of how Ascaris hemoglobin worksto bind oxygen, there are hopes that this could prove successful where otherideas have failed.


ANTIBIOTICS—SURVIVING DISEASE

When most people think of antibiot-ics, they think of penicillin. Even beforethe drug was discovered, scientists wereaware of the antibacterial properties ofthe fungus, Penicillium for over 100 years.It was recognized that the fungus is ableto release a chemical that kill bacteriaand other fungi by attacking their outercell membrane. The research that wastriggered by these observations led tothe isolation of the key chemical (penicil-lin) involved, and the first antibioticmedicine was created. Since then, manyfungi and bacteria have been found toproduce and secrete antibiotic chemicals.Many of these have been exploited bypharmaceutical companies.

Antibiotics are not just used by bacte-ria and fungi, though. All organismscome under attack from bacteria andfungi that can cause serious disease.There is therefore a great selection pres-sure to develop resistance or a counterat-tack to these pathogens. In animals, it isthose species that live communally(humans included) where there is great-est risk of bacterial and fungal disease.Living close together means infectiousagents can easily be passed from oneindividual to another.

The various species of communal ant are perhaps the most close-living of allcommunal animals. Living so close together, they run a high risk of an infec-tion taking hold and wiping out an entire colony of millions of individuals injust a few weeks or even days. It is not surprising, then, that certain species ofant have evolved a solution to the problem. The fierce bull ants of Australiaare one such species that have evolved a defense against bacterial and fungalattack. Over the millions of years they have lived on this earth, they haveevolved glands that secrete antibiotics.

Bull ants have two of these antibiotic-secreting glands, called the metapleu-ral glands, each situated just above the back leg. These glands constantlysecrete a milky fluid that covers the ant’s body. The fluid is packed with power-ful antibiotic chemicals called metapleurins that protect the individual fromfungal and bacterial attack that can be so deadly to tiny insects such as these.


The fungus Cordyceps is one of the few speciesresistant to the antifungal molecules producedby ants. The fungus affects the ant’s braincausing it to clamp its jaws on a leaf in the for-est canopy before it dies. The fungus thengrows from the ant allowing it to disperse.[Gregory G. Dimijian, M.D. / PhotoResearchers, Inc.]

Metapleurins are powerful antibiotics, destroying most bacteria and fungion contact by breaking down their outer cell membrane. As a result, the sur-face of the bull ant is almost entirely free from bacteria and fungi. It is muchcleaner than most human skin. Not all bull ants have the necessary glands toproduce this disinfectant. Unfortunately for the males, it is only the females—the queen and her workers—that are suitably equipped. A male can benefitfrom the protective fluid produced by females by brushing against them. If amale becomes separated from the colony, though, it will soon become badlyinfected. So why have males not evolved this useful gland? In the ant colony,males are fairly useless. Once they mate, they soon die. For their short life theyare protected by the antiseptic produced by the females, but after mating andleaving the nest they quickly die.

Given the huge evolutionary advantage of being able to fight disease, nearlyall species of social ant produce at least one type of antibiotic. Not all speciesproduce such a potent chemical as the bull ant, though. Leaf cutter antsproduce antibiotics in their metapleural glands, but they are only mildly anti-fungal—just enough to afford some protection from disease. The reason forthis is that their food source is a fungus that they farm in their nest. The leavesthat they cut and bring back to their nests are not eaten by the ants but are usedto feed the growing fungus fields that the ants cultivate and eat.

Given the close relationship ants have with fungus, leaf cutter ants haveevolved a very specific array of antifungal chemicals. Each species of leaf cut-ter ant will farm just one species of fungus to feed the colony. The introduc-tion of a different species of fungus to the nest would be disastrous. Not onlywould it be wasteful, but an invading fungus could cause disease in thecolony. Leaf cutter ants are therefore very careful farmers. Their crop of fun-gus is like a field of wheat with no weeds, and to achieve this they have atailored arsenal of weed killers. The saliva of the ants contain antiseptic sothat newly cut leaves can be sterilized before they are brought into the nest.If any fungal spores do find their way into the nest, the ants carry with thema broad range of antifungal chemicals that will attack the ‘‘weed’’ species, butleave the ‘‘crop’’ species alone. Although they do produce their own antibiot-ics, leaf cutter ants get these weed killer antifungal chemicals from bacteria,which they carry with them on their bodies. These bacteria produce andsecrete antibiotics specifically adapted to the nest environment to ensure ahighly productive crop.

The story, however, doesn’t quite end there. As we know all too well fromthe spread of bacteria that are resistant to antibiotics, nature can evolve inresponse to these protective chemicals. Ants, therefore, are not fully immuneto the attack of bacterial and fungal pathogens. A common disease of ants isthe fungus, Cordyceps. This fungus is resistant to the chemicals produced byants and can quickly infect an unsuspecting ant. Not only does it overwhelman infected ant by spreading through its internal organs, but it will manipulatethe unfortunate individual to perform a bizarre behavior in the last moments of


its life. The fungus affects the ant’s brain and causes it to climb a nearby plantand bite down hard on its stem. Jaws clamped over the plant, the ant will die inthis position. From there the fungus can grow from its body and, from itsadvantageous position, release its spores, which are dispersed through the air.

No matter how sophisticated the defense, evolution always seems to pro-duce something one better. The next step will be for ants to evolve a newchemical to resist the current resistant Coryceps. Perhaps then we will have ananswer to our seemingly unstoppable resistant bacteria plaguing our hospitals.


Humans have been manufacturing antibiotics for some 60 years. These anti-biotics have helped millions of people survive potentially deadly diseases andcan be considered one of the most important discoveries of our history. It willperhaps come as little surprise, then, that pharmaceutical companies are seek-ing ways to exploit this recently discovered antibiotic resource in ants. At leasttwo of the antibiotic metapleurins from bull ants have been patented and areused as antiseptics in hospitals. Interestingly, however, although bull-antmetapleurins are a recent discovery in Western medicine, their effects havebeen well known to Australian Aboriginals, who have been using bull ants totreat cuts and scrapes for hundreds of years.

The leaf-cutter ants, too, have been exploited in the production of man-made antibiotics. The antibiotic-producing bacteria they carry with them intheir bodies are called Streptomyces. It is relatives of these bacteria that are usedto produce many of the commercially important antibiotics used today.

PSYCHROPHILES—SURVIVING EXTREME COLD

Life rarely thrives in freezing conditions. The biological molecules thatkeep things ticking over in an organism’s cells slow down and become sluggishas temperatures begin to fall past 32°F (0°C). As a result, the organism itselfwill become lethargic and will eventually freeze to death. A few hardy crea-tures, however, can survive below freezing. They are called psychrophiles,meaning ‘‘ice-loving.’’

Large animals like polar bears can survive on the ice thanks to their huge sizeand warm blood. For smaller, cold-blooded animals, though, life is much moretough. Yet head to theAlaskan glaciers just before dawn and the normally pristinewhite snow will be covered in billions of tiny, threadlike black worms, each oneno bigger than half an inch (1 cm) long. Every one of these worms is from samespecies—Mesenchytraeus solifugus—which is very closely related to the humbleearthworm that burrows through garden soil. Perhaps surprisingly, the ice wormhas very few discernible physical adaptations that allow it to cope with life on theice. Yet it completes its entire life cycle at around 32°F (0°C)—a temperature thatwould easily kill its earthworm cousin.


The ice worms of Alaska keep to a very tight temperature range. They die ifconditions drop to below 19°F (−7°C) or if they creep above 43°F (6°C). If theenvironment gets too warm their bodies disintegrate. As temperatures rise, theice worm’s digestive juices get overactive and begin to attack the body—theywill literally melt in warm conditions. By spending their entire life on and inthe ice they can stay near their optimal temperature. To avoid getting too coldor warm ice worms will migrate through the ice throughout the day, seekingout the ideal temperatures. This is why they spend the day crawling throughtiny cracks in the ice during the day and emerge at night to feed on snow algae.

How does the ice worm cope with the cold? All organisms get their energyfrom the high-energy molecule Adenosine Tri-Phosphate (ATP), which ismade by metabolizing food. When temperatures drop, metabolism slows(as determined by the basic laws of physics), which means that less ATP canbe produced. Without this energy supply, organisms will become sluggishand will eventually die. This is why animals slow down when things get cold.Ice worms, though, have overcome this response to the cold. They can actuallyincrease the amount of ATP (energy) in their cells as temperatures drop. Theyapparently can contravene the physical laws of thermodynamics! This phe-nomenal ability means that they have enough energy to keep moving even astemperatures drop to 43°F (−6°C), the point at which they eventually freezeand die.

This last point had researchers stumped. How can an animal increase therate of ATP production as temperatures drop, seemingly defying physics?It is not clear. The answer is probably that ATP (energy) production stays con-stant regardless of temperature, and it is the efficiency at which ATP is used thatincreases at lower temperatures. In other words, the ice worm becomes moreefficient at burning energy as temperatures drop. This would explain whyenergy levels seem to increase when temperatures fall. This is still an incredi-ble feat, though, and no one is quite sure how it is done. The upshot of it is thateven at 32°F (0°C) ice worms can move around at the same pace that its cousinthe earthworm achieves at 68°F (20°C). They put this mobility to good use inforaging for food. They can move through the snow and ice browsing on algaeor they can be found clinging on to the icy banks of glacial streams and ponds,snapping up passing morsels of food.

The ice worm is the largest animal to live entirely on the ice at freezing tem-peratures, although on the glaciers of Alaska there are other species that canpull off the same feat of energy conservation from three other kingdoms of life.As well as the adaptation being found in animals (the ice worm), it is also seenin bacteria, fungi, and algae, suggesting that the adaptation has evolved morethan once in response to the stresses of life on the ice. What’s more, it has evenevolved thousands of miles away in the Gulf of Mexico right at the bottom ofthe ocean. Here, another worm, which is also called an ‘‘ice worm’’ (althoughcompletely unrelated to the Alaskan ice worm), lives in the frozen methaneice deposits that erupt from the ocean floor.


All of these creatures are able to increase the amount of energy-rich ATPin their cells as temperatures drop, allowing them to keep moving. Fromvarious experiments it seems that this ability is achieved in part by speciallyadapted biological molecules that are involved both with the production ofATP and with the breaking down of ATP to release energy to fuel an organ-ism’s cells.

There are undoubtedly other adaptations the ice worm has evolved to sur-vive in icy glaciers, but these mysteries are as yet unknown. Some secrets arebeginning to be exposed—like the discovery of symbiotic bacteria found livingin the ice worm’s gut, which may be part of the picture. This adaptation needsto be explored further, but it may hold the key to the ice worm’s survival on theice in the extreme winter conditions when surface temperatures fall to below104°F (40°C) and food is very hard to come by.


NASA scientists have recently become very interested in these humble littleworms. Understanding how they can survive in such extreme conditions couldgive valuable insights into what life might be like if ever it were discovered onicy planets such as Europa, one of Jupiter’s moons. More mundane applica-tions of research into ice worms may be in the field of organ transfers. Thesame adaptations that keep ice worms moving at cold conditions may help indeveloping better storage of human organs before transplants.

ANHYDROBIOSIS—SURVIVING WITHOUT WATER

Water is essential for all life, from the tiniest bacteria to the largest mam-mal. It is involved in nearly all the reactionsthat keep an organism’s cells alive, and so itis probably the most important commodityinside any living creature. In humans,water makes up nearly 70 percent of ourbodies, and it needs to be constantlyreplaced because it is lost when we sweat,breathe, and excrete. It is not surprisingthen that most organisms tend to stay awayfrom places where water is hard to comeby. There are several adaptations allowinganimals, plants, bacteria, and fungi to copewith drought, but there are some places onearth that are simply too dry for life topersist. Except, that is, for a few hardycreatures that show some ingenioussolutions to the problem.


Scanning electron micrograph of the tardi-grade. In times of drought, the tardigradefolds its body in on itself and adopts a barrelshape (tun formation). It will also replacethe water in its body with a sugar, trehalose,to prevent damage to its cells. [SteveGschmeissner / Photo Researchers, Inc.]

Probably the driest place of earth is in the McMurdo Valley in Antarctica,where it is so cold that more often than not any available water is frozen solid.Early explorers who dared to enter the frozen wasteland reported that no lifepersisted here at all. However, deep within the desiccated soils there exists ahardy animal that has a remarkable ability to cope without water. It is a curiouscreature called a tardigrade, otherwise known as the water bear. This animalhas no problem in surviving the tough, near-perpetual winters when water isimpossible to come by.

The tardigrade is not a very big animal, such are the tough conditions inwhich it lives. The species living in the Antarctica tend to be no longer than0.5 mm long. This small size could actually be a problem when it comes toretaining water. Small animals have a larger surface area-to-volume ratio thanlarger animals, so there is a larger relative area from which water can be lost.As it happens, though, losing water from the body is not really a problem forthese creatures.

When conditions get too extreme, tardigrades are able to enter what isknown as a cryptobiotic state. Literally, cryptobiotic means ‘‘hidden life,’’and that is a very apt description. You would have to look very hard to findany signs that the animal is not dead when it enters this state. Tardigradesare able to enter a cryptobiotic state in response to a range of conditions, butwhen there is a lack of water, it is called an anhydrobiotic state, meaning ‘‘lifewithout water.’’

In very dry conditions, the tardigrade has to go through a number of stagesbefore it is ready to see out the tough times ahead. First it curls up into a verytight ball to prevent a fatal loss of water. This is not so easy for the tardigrade,which has a distinct head and eight distinct legs. To manage it, its limbs fold inon themselves so they are tucked inside its body and its body folds inward so itturns from a recognizable animal into an indistinct oval blob. It is a little like atortoise retreating into its shell, but instead of simply drawing in its head andlegs it actually inverts them inside its body. This stage is called tun-formation because the end product looks very much like the tun barrels usedto store beer.

In very dry conditions, the tardigrade can cope with extreme water loss.When they enter the anhydrobiotic state, their bodies have only 1 percent ofthe water they normally hold. On its own, this would clearly be a problem—their bodies would collapse in on themselves, causing irreparable damage.The tardigrade has a neat solution. It replaces the water with a sugar, treha-lose, that protects their organs from the damage normally associated with des-iccation. It is a like filling their bodies with a jelly.

Of course, once fully tucked up and stuffed with protective trehalose, thetardigrade can’t hunt for food. That is why it must reduce its metabolic rateto next to nothing to avoid wasting energy. During anhydrobiosis, its meta-bolic rate falls to just 0.01 percent of its normal level. With such low metabo-lism, these hardy creatures burn practically no energy whatsoever. There have


been some claims that tardigrades can survive for up to century in this state,although this is likely to be false. There is evidence, though, that they can sur-vive for up to 10 years in an anhydrobiotic state. Perhaps what is even moreremarkable is that is only takes a few drops of water for the tardigrades to snapout of their living death and return to their normal state of being in just a fewshort hours.

It is not only tardigrades that can survive in the driest place on earth. Theyshare the soils of the McMurdo dry valleys with three species of nematodeworm that can enter the same anhydrobiotic state when there is no water tobe found. These worms are slightly larger than the tardigrade, being onlyabout 0.04 inches (1 mm) long. Tun formation is slightly easier for them—having no limbs, they can easily coil up. But they too replace their body waterwith trehalose sugar and reduce their metabolism to the bare minimum.

Tardigrades are indeed a hardy group of animals. They can enter acryptobiotic state to avoid a range of conditions. They can tolerate very saltyconditions, very acid conditions, and extreme temperatures—from close toabsolute zero (the coldest possible temperature) to up to 480°F (250°C—hotter than a kitchen oven). Amazingly, as a by-product of their resilienceto these natural (if extreme) conditions, they are also able to withstand manyother potentially fatal conditions. They can survive bombardment by poten-tially damaging X-rays, the conditions inside a vacuum, and pressures equiv-alent to 6,000 atmospheres. Despite their small size and unassumingappearance they are truly one of the most hardy creatures on this planetand have been able to fashion a niche out of exploiting habitats that othercreatures simply cannot survive.


So fascinated by tardigrades’ ability to survive, and perhaps spurred on by adesire to find out what, if anything, might kill a tardigrade, on September 14,2007, scientists sent tardigrades into space as part of the Tardigrades In Space(TARDIS) program launched by the European Space Agency. The aim of theprogram is to explore the impact of space travel of such animals, possibly withthe view of their use in any future projects to colonize other planets.

PRIONS—SURVIVING EVERYTHING

To flourish, living organisms must cope with many adverse conditions—thecold, heat, radiation, too much or too little water, immunological defenses, toomuch or too little salt, poisonous chemicals . . . the list goes on. All these envi-ronmental conditions can attack an organism’s body and the genetic materialthat controls how that body works. Those individuals or species that succumbto these adverse conditions will suffer or even die. The ones that have adapta-tions to survive these conditions, though, will enjoy a huge competitive


advantage over those that cannot andwill be evolutionarily successful as aresult. Many adaptations have evolvedto cope with these pressures, some ofwhich have been covered elsewhere inthis book. There is one group of organ-ism, though, that has taken the art ofsurvival to the extreme. These creaturesare the simplest form of life on earth,and they are pretty much resistant toanything that is thrown at them. Theyare the prions.

The ability of prions to survive isbased on simplicity. They have no body,nor even what we might recognize asgenetic material—they have no DNA.For this reason, some scientists ques-tion whether they can be considered tobe alive at all. But they can replicatethemselves, and on this definition wemight consider them to be like anyother living organism.

Like viruses, prions are infectious organisms. They cause the degenerativediseases called Transmissible Spongiform Encephalitis (TSE) diseases. TSEsinclude degenerative brain diseases in humans such as Creutzfeldt-Jakobdisease (CJD) and fatal familial insomnia. The latter is an inherited disease thataffects the thalamus in the brain, causing complete sleeplessness and eventuallydeath. Another well-known TSE disease is Bovine Spongiform Encephalitis(BSE) in cows, otherwise known as ‘‘mad cow disease.’’

So what are prions? Very simply, they are pieces of protein that can makemore copies of themselves. This makes them very much like DNA, thoughunlike DNA they make copies of themselves by converting normal, uninfec-tious proteins that are already in a host’s body into the infectious prion form.In humans, the ‘‘normal’’ protein is an important antioxidant protein that isfound on the surface of our cells. If a human body is infected with a prion, this‘‘vampire protein’’ will manipulate the shape of any normal antioxidant proteinthat it comes across and convert it into another prion protein. The newlyformed prion protein is then capable of converting other normal antioxidantproteins and so on.

As prions get to work, they cluster together to form a protein plaque calledan ‘‘amyloid,’’ causing holes to develop in the infected tissue, typically thebrain, which gives the tissue its characteristic ‘‘spongy’’ look. After infection,death may be a long time in coming, but it is a certain death as the brain gradu-ally becomes destroyed. Despite being so methodical a killer, prion diseases are


Prions are disease-causing proteins that convertnormal proteins into copies of themselves.On the left is a computer simulation of thenormal-shaped protein. On the right is thedisease-causing prion. The prion is made ofmany rigid protein sheets (shown as arrows inthe simulation) which makes it extremely resil-ient. [AP Photo / Professors Stanley Pruisner /Fred Cohen, University of California–SanFrancisco Medical School]

not common because they have a very poor mode of infecting new hosts. Infec-tion is by ingestion, which entails the rather gruesome (to humans anyway)business of eating infected brain material. It was for this reason that the other-wise very rare degenerative disease Kuru was so common to the indigenouspeoples of Papua New Guinea. The tribe members were cannibals who atethe brains (and everything else) of the dead.

Methodical though prions are at converting normal proteins, a key part oftheir success has come through the remarkable resilience to more or less anyattack. They are extremely heat resistant. Easily coping with temperatures of175°F (80°C), prions can even survive, for a short period at least, temperaturesof over 212°F (100°C). They are resistant to ultraviolet (UV) radiation andionizing radiation, both of which are so damaging to DNA. They are alsoresistant to an animal host’s defenses, which would normally destroy foreignproteins. This means that they can survive well both inside the host body andoutside. They are capable of lying dormant, waiting to be consumed byanother unwitting host.

The secret to this incredibly effective adaptation lies in the structure ofthe protein. The cells of all living organisms make a group of proteins calledenzymes. These are proteins that bind to other molecules in the body andeither join them to other molecules or break them down to smaller mole-cules. Enzymes are critical in both the growth of the body and the breakingdown of food. In any of these reactions, it is largely the enzyme’s shape thatis important. They must bind to the other molecule in a specific way tochange it. Enzyme reactions have therefore been likened to a key fittinginside a lock—get the wrong key and the lock won’t open. Prions are exactlythe same. It is their shape that is key to changing the normal proteins intoprion proteins.

It so happens that the particular shape required to convert the normal pro-tein to the infectious type also conveys a prion’s powerfully resistant proper-ties. All proteins are made up of building blocks (amino acids) that are heldtogether as either loose ‘‘strings’’ or rigid ‘‘sheets.’’ The normal protein thatis used as an antioxidant is made up mostly of these loose strings. Once is ittransformed into the infectious prion form, however, many of these loosestrings are converted to the much stronger sheets, giving the prion greatstrength that can resist extreme heat, cold, and radiation.

So, how did this unusual group of organisms evolve? It is not at all clear. It islikely that a mutation in the host’s DNA that codes for the normal protein cre-ated the prion form. Normally, such a mistake would rapidly become extinctthrough the normal processes of natural selection, but thanks to the prion’sability to replicate itself and survive for long enough to infect a new host itwas suddenly able to survive as an independent organism, no longer simply aproduct of the host’s genome. This may sound incredibly unlikely, but this,after all, is what evolution and adaptation are all about—chance mutations thatturn out to be successful.



Prions are a fascinating group of organisms that are not well understood.Scientists are increasingly turning their attention to these simple proteins,however, mostly to understand the risk of transfer of bovine prions to humans(the link between BSE and CJD). An interesting side effect of this research isthat by better understanding prions and how they affect the brain, scientistsare hoping to learn more about more common degenerative brain diseases likeAlzheimer’s disease and Parkinson’s disease, which currently afflict millions ofpeople.


3

LOCOMOTION

LOCOMOTION—HUMAN INVENTION

The first recognizable human ancestor appeared on the planet some 2.5 millionyears ago. From their origins in Africa, our ancestors moved first into Eurasiaabout 1 million years ago and began colonizing western Europe about500,000 years later. From here, humans spread to Australasia about40,000 years ago. East Asia was reached by 20,000 BC, and from there NorthAmerica was colonized in 12,000 BC. Humans continued their migration andhad reached South America by 10,000 BC. Our arrival into the colder climatesof Greenland was much more recent—happening at around 2,000 BC. Thespread of humans across the planet has been impressive, certainly as a resultof human adaptations that have allowed us to use tools to find food and keepwarm. It is equally true, though, that certain colonization events could onlyhave taken place thanks to the design and construction of human modes oftransport.

To colonize certain parts of the globe, humans would have had to cross sig-nificant bodies of water, which means that our ancestors would have had tobuild boats. It is likely that the first of these were simple rafts, little more thanhumans resting on trunks and branches and drifting across the ocean. Thesetree trunks could have next been hollowed out to make early canoes. After this,human would have constructed simple coracles, which are more complexcanoes made by stretching animal skins over a wooden frame. Even these basicdesigns were sufficient to exploit much of the land masses on the planet.

One of the important steps in human evolution was the move from a hunter-gatherer way of life to an agricultural one, which led to the gradual domestica-tion of animals. The first to be domesticated was the dog at around 10,000 BC,

most likely used as a pet and to assist with hunting. However, around 4,000 BC

the horse was domesticated and rapidly became a mode of transport ratherthan simply a source of food. Evidence of humans using the horse for movingaround comes from the steppes of the Urals about 3500 BC. Graves from2500 BC include horses buried with chariots, suggesting that human societiesat this time had harnessed the power of the horse to draw carriages.

Horses fulfilled the vast majority of personal human transport needs fornearly 6,000 years until 1866 when Nikolaus Otto built the first gas-poweredengine. These engines were fitted to bicycles to create the first motorcyclesin 1885 and were soon fitted to a truck in 1896. Even at the turn of the twen-tieth century, automobiles were expensive and not especially high powered,but they have since been redesigned and refined to produce vehicles capableof covering hundreds of miles in a day.

The internal combustion engine that lies at the heart of most cars is basedon the principles of steam power that had been designed centuries before.The first steam engine was built in 1698 by an Englishman, Thomas Savery,using a fairly simple design. Fuel is burnt to heat water and generate steam inorder to drive a turbine, which in turn can be used to drive wheels. This, ofcourse, opened the door to the whole industrial revolution as well as masstransit systems such as trains and ocean liners. Car engines work very muchin the same way. Controlled explosions of fuel drive pistons up and down,which turn crank shafts to drive the wheels of the vehicle. It really is the auto-mobile that has taken the next step in giving humans such personal freedom toget from point A to point B.

Improvements to the automobile for moving across land continue to bemade to the extent that we now impose speed limits on our roads to protectour safety. This moved the quest for speed to the flat salt plains of the desert,where a vehicle can, with moderate safety, accelerate to whatever speeds it iscapable of. In 1999 British engineers produced a vehicle that reached speedsof 763 miles per hour. The same team is currently planning a vehicle that canbreak the 1,000 miles per hour mark—faster than a bullet fired from a gun.This vehicle, called the Bloodhound, is powered by a rocket strapped to a jetengine and requires bodywork capable of withstanding pressures of 1 ton persquare foot (12 tons per square meter).

The trick with such fast-moving land vehicles is keeping them on theground, as often they get sucked into the air and flip. This is not a problemfor aircraft that actually want to be sucked into the air. Lift is generated byair flowing over an object at a faster speed above the object than below it. Thiscreates higher air pressure below the object than above it, pushing it into theair. The design of airplane wings is based entirely on the process of air flowingover them in this way. In cross-section, an aerofoil wing is flat at the bottomand curved on the top. With air having to travel further over the top of thewing than below it, air above the wing moves faster, creating the requireddifferential in air pressure.


Once in the air, the speeds achieved on the ground can easily be reached andpassed because there is much less drag. The fastest unmanned aircraft cur-rently is the X-43, which travels at speeds of more than 7,000 miles per hour.The fastest manned aircraft is probably the Lockheed’s SR-71 (the Blackbird),which made its maiden flight on December 22, 1964 and has achieved speedsof over 2,000 miles per hour, nearly three times the speed of sound. The keyto achieving these tremendous air speeds has been the invention of the jetengine.

The thrust produced by a jet engine is really an extension of the simplepropeller engines seen on early aircraft and still used in smaller planes today.A fan sucks air into the engine, where is passes through a compressor thatcondenses the air and puts it under pressure. In the compressed air, fuel isburnt, which drives a turbine that forces the air and fuel exhaust from theengine and drives it forward. The SR-71’s engines were related to this basicjet engine design, but instead of using a fan to suck in the air it used itsown forward momentum, giving the engine its name, the ramjet. The engineused by the high-speed X-43 is another variation on the jet engine themecalled a scramjet.

The speed of manned aircraft has not exceeded those of the SR-71 becausefast-moving aircraft and land vehicles are notoriously hard to maneuver. Eventhe slightest movement away from traveling in a straight line can result indisaster at high speeds. Modern aircraft used for the military need to compro-mise speed for agility. Probably the most advanced military aircraft is theEurofighter, which travels at a relatively modest top speed of 1,500 miles perhour. It is incredibly agile, though, thanks to a very un-aerodynamic design.A complicated computer system is needed to keep the plane airborne—withoutit the craft would drop from the sky. This innate lack of stability, however,gives the aircraft excellent maneuverability.

Both air and land vehicles are driven by designs that rely on the principle ofturning a wheel. Piston-driven crank shafts drive the wheels of cars, and pro-pellers drive the jet engines of airplanes. Even the helicopter is lifted fromthe ground by a propeller. Human engineering for water-bound vehicles isno different. The propeller is used to drive boats, submarines, and even torpe-does. Much like the jet engine, the impeller is an invention that compresseswater after it is sucked into an aquatic ‘‘engine’’ by a propeller fan so that it isexpelled at a greater pressure, generating more thrust.

Perhaps the one exception to this reliance on a spinning wheel or propellerto generate thrust is the use of rockets, which involves the expelling of high-pressure fuel exhaust from the end of a vehicle to generate thrust. Initially, thisform of propulsion was seen only in missiles and fireworks, but it is the mainform of propulsion that has driven spacecraft since man first orbited the earth.Rocket propulsion is not especially rapid, though, especially when trying tocover the vast distances between planets in space. NASA is hoping to changethis with its variable specific impulse magnetoplasma rocket, or VASIMR.

LOCOMOTION 57

The VASIMR engine is a plasma-based propulsion system. Plasma is aunique state of matter different from solid, liquid, or gas. Perhaps it is bestdescribed as being an ionized (electrically charged) gas-like substance. Theimportant feature of plasma is that it can be directed by magnetic fields, whichis what the VASIMR engine does. Electric fields heat the hydrogen-basedplasma like any rocket fuel and the magnetic field directs it as it is ejected fromthe engine, allowing for a high amount of precisely directed thrust. The benefitof such an engine is that the fuel, hydrogen, is extremely common in space sohuge fuel tanks would not be needed. Such an engine may help humans in theirdesire to step foot on relatively nearby planets such as Mars, but a completelynew type of engine would need to be designed to travel further. There is stillplenty of engineering required before we can fully realize the dream of travel-ing huge distances to fully explore the universe.

BIRD FLIGHT

Early attempts at flight by humans met with spectacular failure. As OrvilleWright, who finally cracked man-made flight, put it: ‘‘We got plenty of flyingfever from watching the birds, but we got nothing about their secret ofbalance.’’ This secret of balance lies in a bird’s wing, and it took many yearsto understand exactly how it works to generate both lift and thrust.

To generate lift, a bird’s wing must have a particular shape, known as anaerofoil. This is important because lift is generated by the way in which airflows over the wing. In cross-section, a bird’s wing looks like a lopsided tear-

drop—this is the classic aerofoil shape.Thanks to the way that it is curved, airflowing over the top of the wing movesquicker than air flowing underneath. As aresult, the wing generates an area of lowpressure above it and an area of high pres-sure below it. This both pushes and dragsthe wing upward, creating lift. All birds,although they may have slightly differentshaped wings, generate lift this way—thisis how they can become airborne and fly.

By subtly adjusting the position of itswings, a bird can maneuver itself with greatagility through the air. When it flaps itswings down, a bird will hold its wings outflat so as to generate as much lift as pos-sible. When it brings its wings back upagain it draws them closer to its body toreduce the effect of drag though the air.Even by drawing in their wings in the


The ruby-throated hummingbird, Archilo-chus colubris. Hummingbirds are uniqueamong birds in their ability to beat theirwings in a figure-eight, generating nearlycontinual lift and allowing them to hoverand even fly backward. [Millard H. Sharp /Photo Researchers, Inc.]

upstroke there is still some drag caused by the turbulent flow of air over thewings when held in the position. This could be disastrous for the bird andcould cause it to drop from the skies if it wasn’t for a neat adaptation. In thefront of the wing there lies a small, finger-like limb called the alula. Indeed,since wings have evolved from the finger bones of birds’ ancestors, the alulareally is a small finger—an evolutionary remnant of the second digit.

The alula acts to smooth the turbulent air flowing over the wing during theupstroke. In the downstroke, the limb is neatly tucked into the wing and is con-cealed from view. On the upstroke, though, it is forced out and away from thewing to create a gap between it and the leading edge of the wing. Some of theturbulent air flows between this gap so that the air flowing over the wing ismuch smoother and the risk of stalling in midair is reduced. In aerodynamics,this effect is called the slot effect. There is no muscular control of the alula;it simply moves into position because of the air pressure passing over it. Thishappens at exactly the right time to prevent the bird from stalling and havinga nasty accident. The same effect is achieved by spreading the feathers at thetip of the wing. They will open out and create a gap that generates lift andthrust throughout the up and down flap.

It is not just the wing that generates lift. The tail plays an important part tooby ensuring the right flow of air over the bird to produce lift and thrust.By coordinating the position of their tail and wings, birds can achieve aremarkable range of aerobatic skills. One of the most quick and agile birds isthe common swift, a migratory bird that flies each year from sub-SaharanAfrica to Scandinavia and Russia and back again, each one-way trip covering70,000 miles. Covering such huge distances is a major undertaking and isfraught with danger. The swift, however, is well designed for the task.

Its body is designed to cut through the air with minimum resistance. It has acompact and streamlined body, and its wings are long and pointed. The swift’swing bones are thick and strong near its thorax, which means that the energyfrom the wing muscles can be efficiently transferred to the wing itself. As aresult, the swift can beat its wings quickly and with considerable force,allowing it to reach high speeds of up to 60 meters per second or 130 milesper hour. From their stocky base, the wing bones taper out into a long andmobile skeleton extending to the tip of the wing. This gives the swift tremen-dous control over its wing, which allows for high agility.

The swift’s agility is put to good use. It lives nearly its whole life on thewing. It will fly with its beak open to collect small flying insects, and it willswoop down to drink from bodies of water. It will even sleep and mate in theair. The only time it will come in to land is to lay eggs and tend the brood.It can rest while in flight by switching off half its brain at a time, a little likeflying on autopilot—another amazing adaptation for this consummate pilot.

The birds with the greatest agility, though, are the hummingbirds. At only 2to 2.5 inches (5–6 cm) long and weighing just 0.004 lbs (1.9 grams), the beehummingbird is one of the smallest warmblooded animals on the planet.

LOCOMOTION 59

Despite its small size, including a tiny heart and lungs, the bee hummingbird iscapable of some of the fastest and most agile movements seen among the birds.Not surprising for such an active animal, it has a very high metabolic rate togive energy to its muscles.

The fuel of choice for the bee hummingbird is the energy-rich, sugary fluidnectar produced in the flowers of plants. But therein lies a problem. Despite itstiny stature, even the bee hummingbird cannot perch on the delicate flowers toget at their nectar. To overcome this challenge, the bee hummingbird hasevolved a complex wing structure that allows it to perform some highly spec-tacular aerobatics to get at their food. Unlike other birds, hummingbirds areable to hover and maintain their position in the air, giving them time to diptheir beak into the flower without needing to alight on it.

Bird wings are typically hinged at the shoulder joint, which restricts theirmovement to a basic up and down ‘‘flap.’’ The bee hummingbird, like allhummingbirds, lack this restrictive hinge and so can beat their wings in a fig-ure of eight. Moving the wings in this way generates near continuous lift,which differs from other birds that generate lift only in the downward flap.What’s more, the bee hummingbird can beat its wings at some 80 to 200times a second. Thanks to this ability to move their wings unconstrained athigh speed, the bee hummingbird can maintain a highly precise control overits flight. It can fly forward, backward, sideways, and even upside down.Consequently, it can hover and maintain a constant position in the air,allowing it to get to its favorite food.


As Orville Wright commented, birds have long been the inspiration forhuman flight. Understanding how the aerofoil works and the ‘‘slot’’ effect ofthe alula on the wing have been transferred directly to aviation engineeringto give our modern planes lift and to control the effects of turbulent air, whichcould cause a plane to stall and drop from the skies.

INSECT FLIGHT

Insects are one of the most diverse and abundant orders of life that inhabitthe planet. It is fair to say that insects owe much of this evolutionary successto their ability to fly. Compared with their flightless cousins, insects that canfly have better opportunities for finding food and mates, evading predators,and colonizing new habitats. As with any group of animals, different insectsspecialize in different types of flight behaviors. The Monarch butterfly,a fairly fragile and weak-looking animal, is capable of a huge migration acrosscontinents for around 3,000 miles (5,000 km). Other insects like the familiarhousefly show a speed and agility that put the most advanced jet planes toshame.


There is no doubting the ability ofinsects to fly well. Just how they do it,though, has baffled scientists for manydecades. Insect flight, at first glance,seems improbable. Insects seem in somecases too heavy for their wings to liftthem or too small and weak to beat theirwings fast enough, or simply that theway in which they beat their wingsshouldn’t generate any lift. In short, judg-ing by conventional aerodynamics, mostinsects should not be able to get off theground at all. But insects are not both-ered about the theory of conventionalaerodynamics. They do things differentlyfrom human engineers and even frombirds, and the evidence is there for all tosee—insects fly extremely well, indeed.

The power to generate the necessarylift and thrust comes from an insect’swings and strong thoracic (chest)muscles. These are very efficient musclesthat deliver a lot of power over a longperiod of time. Hoverflies can hover inmidair because they can beat their wings1,000 times a second. The muscles arealso capable of delivering huge bursts ofspeed. Tropical bees and wasps can travel up to 45 miles per hour thanks tomuscle power output that is some 30 times that of a human leg muscle.

But what about lift? Bird wings create lift because they are shaped like anaerofoil. Air passing over the wing generates a differential in air pressure oneither side of the wing, resulting in upward thrust and keeping the bird in theair. Insect wings are very different. For one, they are flat and not at all shapedlike an aerofoil. To generate the right flow of air over their wings they must usethem in various ingenious ways. The key to their success comes from exploit-ing a phenomenon called vortices. A vortex is a swirling pocket of air or liquid.You can see this if you dip your hand in any still body of water (a bath, pool, orsink full of water) and slowly move it in any direction. You should see littlewhirlpools form on either side of your hand. These are vortices.

When you move your hand through water, the whirlpools will tend to movewith your hand, almost as if they were stuck to it. If you were to move yourhand quicker they could become unstuck and be shed from your hand. Thesame happens in insect flight. The insect will beat its wing so the vortex thatforms on the leading edge (the front edge of the wing) stays put. If you could

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A high-speed photograph showing the lift-generating vortices produced by a butterfly asit takes off vertically. [Dr. John Brackenbury /Photo Researchers, Inc.]

see the vortex in the air (which you can’t unless you blow smoke or somethingvisible over the wing) you would see the little whirlpool of air on the front andtop edge of the wing. This in effect creates an aerofoil over the insect’s flatwing. Air has to go around the vortex, so the airflow over the wing is nowexactly like that over an airplane’s wing or a bird’s wing. It creates a differentialin air pressure that effectively sucks the wing upward, creating lift.

Vortices formed at the back of the wing—the trailing edge—do not typicallystick to the wing like they do at the leading edge. These vortices that are shedfrom the wing are put to good use too. Thanks to a complicated way of beatingtheir wings, insects can use the shed vortex to generate lift on the upstroke aswell as on the downstroke. (Birds generally only get lift from the downstroke.)By moving its wing through a shed vortex on the upstroke, an insect can gainlift thanks to the way air pressures differ on either side of the wing. It isthought that interacting with shed vortices in this way generates two to threetimes more lift than flapping alone and gaining lift just from the downstroke.

The use of vortices is certainly a great solution for otherwise cumbersomeinsects to be able to fly. It exploits some complicated physics, and it has onlyrecently been understood how insects manage to do it. In fact, the physics ofvortices and how to generate them over the wing in just the right way is anextremely precise art for insects to achieve. Often they must position theirwings in such a way that they are always on the cusp of stalling and droppingout of the air. This precision has been fine-tuned over millions of years of evo-lution, however, and insects no more think about it than you or I do withbreathing in and out.

Having mastered the physics of flight, insects have evolved several adapta-tions to conquer the air. It is the design and arrangement of the wings them-selves, though, that determine how agile the insect can fly. Insects have oneor two sets of wings. Having two pairs of wings, like the dragonfly, is the basicmodel, although a lot can be done with this simple piece of kit. Dragonflies areagile creatures capable of impressive midair acrobatics. In a tight turn, theseminiature air aces can exert a force of 2.5 G, which is impressive for a creaturethe size of a small pencil.

Two wings moving independently is not particularly aerodynamic, though.Some insects have therefore evolved to fly with just one set of wings. Insectslike house flies, horseflies, and robber flies are extremely quick and agile thanksto the gradual reduction in size, throughout their evolution, of their secondpair of wings. The reduced wings are not entirely useless, though, and indeedthey play a critical role in keeping two-winged flies balanced in the air.

If you look closely at the hind-wings of a modern house fly you will see thetwo very tiny wings that have a rounded, clubbed end. These vestigial wings,called halteres, have evolved to be highly efficient balancing organs. When ahouse fly is airborne, the halteres beat in time the normal forewings, but justout of phase. Thanks to the heavy clubbed end of the organs, the halteres beatin one particular direction, like the pendulum of a clock. If the insect makes a


sudden change of direction—either intentionally or due to a sudden gust ofwind—the stem of the haltere will twist. This twisting is detected by a densecluster of nerve endings attached to the haltere, and the information is fed tothe brain so the fly can take the appropriate action to stay at altitude and oncourse. The result is a fast flying, highly agile animal that is nigh on impossibleto catch.

The fossil record reveals just how successful this design for flight has been.It gives evidence for there being winged insects for some 305 millions years.Furthermore, unlike birds, which have had to adapt existing limbs to evolvewings and flight, insects have kept all six legs, which means that they enjoythe benefits of active living both in the air and on the ground. Insect wingsare versatile adaptations allowing fast flight, hovering, and breathtaking airacrobatics. It is thanks to these adaptations for flight that have allowed insectsto dominate the animal kingdom and spread so prolifically on this planet.


Recent insights into how insects manipulate vortices around their wings ishelping engineers produce insect-like micro air vehicles (MAVs). MAVdesigners are looking to the unconventional way in which insects flap theirwings to get their tiny vehicles airborne and mobile. MAVs are very much intheir infancy, but they do hold great potential for survey and mapping workas well for the military. Understanding how insects stay in the air is key tounlocking this great potential.

RUNNING

Running is about speed and endurance. Some animals are natural sprinters,others are more long-distance runners. For whatever the purpose, runninginvolves a complex series of movements that are very different from walking.Given that running fast or for long periods of time can make the differencebetween getting a meal or going hungry (or indeed being a meal or stayingalive) it is not surprising that there have evolved several useful adaptations inthe animal kingdom to hone the art of running.

As anyone who has tried to get close to one in the wild can attest, lizards arequick sprinters, yet they cannot run fast for long for the very good reason thatthey are physically unable to breathe while running. Without the oxygenneeded to refuel their cells, a lizard’s muscles will become exhausted afterabout a minute or two. It can take hours to recover the energy. As a result,running lizards will stop frequently to catch their breath before they becomecompletely exhausted.

The problem for lizards lies in their anatomy. Their legs and feet are posi-tioned to the side of their body, which means they run and walk in a sprawl-ing, swaying motion. Each step results in the body twisting left and right.

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When a lizard steps with its right foot, its body flexes to the left and squeezesair from its left lung. What’s more, the muscles that are used to move theribs and inflate the lungs are the same muscles that are used to move thetrunk while walking and running, and they can only do one job at a time.When it walks, therefore, a lizard can only breathe with both lungs whenits body is straight between steps. At walking pace this is fine, and the lizardcan get enough oxygen to its muscles by using only one lung at a time. Whenit starts running, however, the body flexes so frequently that there is notenough time for either lung to fully inflate. Holding their breath, lizardscan run for long enough to escape predators or to catch its prey, but notfor much longer.

Other reptiles have evolved ways around the problem of running andbreathing at the same time. Crocodiles and alligators use part of their pelvis,their pubic bone, to allow the lungs to inflate while running. In addition toinflating the lungs by expanding the rib cage, alligators and crocodiles can doso by pulling the liver toward the tail. This works a little like the diaphragmin humans; by pulling the liver down, pressure in the chest cavity is reducedand causes air to rush in to the lungs. The key here is a hinge joint in the pelvisthat allows the pubic bone to swing out of the way to allow the liver to bepulled toward the tail. When the alligator breathes out, the liver is pulled backinto place and the pubic bone swings back to its original position. Birds use a


The cheetah, Acinonyx jubatus, in full stride. Its flexible spine allows it to take strides ofup to 23 feet (7 m). [G. Ronald Austing / Photo Researchers, Inc.]

similar method to breathe, and it has been suggested that dinosaurs may havedone so too, allowing them to be active for prolonged periods of time.

Certain reptiles, then, have evolved an adaptation that allow them to runand breathe at the same time. The true masters of running, though, are themammals, some of which have evolved in such a way that their entire bodiesare adapted for speed and endurance. Mammals have their limbs below theirbody and a flexible spine, both of which allow for movements that efficientlytransfer power from the muscles into forward momentum. The spine and bodymovements during running allow the lungs to fully inflate, which provides forsufficient oxygen to sustain the hardworking muscles.

The best-known sprinter is the cheetah. It can reach speeds of 70 miles perhour and accelerate to this speed in about three seconds. The power to get tothese speeds comes from the muscles, which are packed with ‘‘fast-twitch’’fibers that contract quickly and powerfully and can continue to work even inanaerobic conditions (when the muscles are starved of oxygen). Fast-twitchfibers are balanced with slow-twitch fibers, which are used for endurance run-ning and walking. Cheetahs have a 20 percent higher concentration of fast-twitch fibers than other fast-running mammals such as the horse or greyhound.

For the muscles to be used efficiently, the cheetah has a highly adapted skel-eton for running. It is designed to allow a huge stride length, some 23 feet(7 m) at full speed, and it can complete four strides each second. This strideis possible only from having such a flexible spine, which not only gives thecheetah a long stride length but also gives extra energy to the running animal.When it bends, it stores energy, which is released when the spine springs outstraight again. Further range in movement is permitted because of the waythe hips are allowed to pivot and because the shoulders are not attached tothe collarbone.

The cheetah is well-adapted to sprinting. In addition to powerful musclesand a flexible skeleton, the cheetah has enlarged nostrils, sinuses, lungs, andheart to get oxygen into the blood and to the muscles. It also has a huge respi-ratory capacity and is able to take 150 breaths per minute—double whathumans are capable of. The animal is extremely light, weighing only 77 pounds(35 kg). In fact, it is so light that this could potentially cause problems with sta-bility when at it is running at top speed and needing to change direction.To counteract this, the cheetah has specialized paws that have only partiallyretractable claws. (All other cats can fully retract their claws.) These claws actlike running spikes, giving extra grip over tricky terrain. Furthermore, theelongated, dog-like pads on the soles of the paws give more traction than theround pads of other cats. Finally, there is the cheetah’s tail, which helps stabi-lize and steer the cat while in full flight.

Although they are excellent sprinters, cheetahs cannot keep up their pacefor long. Other animals specialize in long-distance endurance running.Dogs and horses are both excellent long-distance runners, but perhaps thebest long-distance runner is Homo sapiens. The skin that is covered in sweat

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glands prevents overheating, but humans also have a wealth of other adapta-tions that make them excellent endurance athletes. Long tendons in ourlegs store energy with each step and release it when our feet spring forward.We are well-balanced too. Swinging arms, a twisting torso, and strongmuscles that keep our head still all allow for efficient distance running. Evenhuman buttocks, which are much larger in humans than other animals, aredesigned as a counterbalance for when we run. All this combined witha highly efficient cooling system means that we can keep running for mileafter mile.


The study of locomotion in humans has been put to use for athletes whoseek to learn more efficient ways of running and jumping to better theirperformance on the track. Studies of animals provide important informationfor walking robots that are able to cover tricky terrain in areas wherehumans or conventional vehicles can’t go, such as over the surface of otherplanets.

SWIMMING—BLUEFIN TUNA

All life found in the seas and oceansmoves around in one of two ways. Thefirst is to simply drift along at the mercyof the tides and currents of the ocean.Organisms that have evolved this formof locomotion are called plankton, mean-ing ‘‘drifting.’’ Planktonic organismsinclude single-celled bacteria, the quirky

diatoms and dinoflagellates, and certain small invertebrates. The developingoffspring of larger animals are often planktonic.

The second way is for an organism to move under its own steam. Theseanimals are sometimes referred to as nekton, meaning ‘‘swimming.’’ The ani-mals that have evolved their own means of locomotion tend to be relativelylarge vertebrates. Within this group of animals several adaptations haveevolved for high-speed movement through water, most of which are seen inone of the fastest swimmers on the planet—the tuna fish. There are severalspecies of tuna, the largest and fastest being the Northern bluefin tuna(Thunnus thynnus).

Movement through water is difficult because it is a very dense medium.Much more energy is needed to propel an object through water than throughair. To overcome this, tuna are well adapted both to generate a huge amountof thrust to propel them through the water and to reduce the drag on theirbody as they move.


The bluefin tuna, Thunnus thynnus. [RichardEllis / Photo Researchers, Inc.]

Some fish generate thrust through gentle flicks of their various fins. This isfine for meandering through reefs to pick at tiny morsels of food, but it is nogood for rapid movement in the open ocean. Faster-moving fish undulate theirwhole body to drive themselves through the water. In part, this is what thebluefin tuna does. Using densely packed, powerful muscles in its body, it drivesits tail from side to side to create thrust. Unlike other fish, though, it keeps thefront part of its body absolutely still to reduce drag.

Bluefin tuna are essentially made of muscle, which is why they are so soughtafter by fishermen. Contractions of these strong muscles pull on two tendons,one on each side of the body, which are connected to the tail fin. There are twotypes of muscle that bluefin tuna employ. The outer layer of muscle is made upof ‘‘slow-twitch’’ muscle fibers. These muscles burn energy with oxygen(aerobic respiration) and are used for long-distance cruising. Below thesemuscles are the powerful muscles used for quick bursts of speed to make a killor escape from danger. These muscles are made from ‘‘fast-twitch’’ musclefibers that burn energy at a much higher rate and in the absence of oxygen(anaerobic respiration). The fast-twitch muscles soon build up high levels oflactic acid and become rapidly fatigued, so they can only be used for shortsprints rather than long-distance swimming.

Tuna’s fast-contracting muscles burn a huge amount of energy to generatethe power required for swift swimming. This means that even at cruisingspeed, bluefin tuna have a high rate of metabolism. To support this metabo-lism, the tuna’s muscles need to be enriched with oxygen in the blood. How-ever, because the bluefin tuna has such a rigid head to stop it from movingabout when it moves its tail, it cannot actively pump water over its gills likeother species of fish. Therefore, to get oxygen out of the water, bluefin tunause a process called ram ventilation. The very act of swimming quickly throughthe water forces water over the gills. This means that if the fish stops swim-ming it will not get the oxygen it needs and it will die. The gills themselvesare densely packed with capillaries to extract oxygen from the water. To getthe oxygen to the muscles, bluefin tuna have a specialized heart. It is pyramidshaped and highly muscled to pump blood quickly through the body.

The muscles provide the power, but this needs to be put to good use. It is nogood generating a lot of power with an inefficient propulsion system. The keyadaptation for fast swimmers like the bluefin tuna is therefore the specializeddesign of the tail fin. The muscles in the tail of the fish contract in a wave sowater is pushed along the body to the tail fin. The fin must release this waterin such a way as to push the fish forward.

The bluefin tuna (and other swift swimmers like marlin and sailfish) have asickle-shaped tail fin. Furthermore, the part of the tail immediately in frontof the fin, called the caudal peduncle, is very narrow and flat like a coin stand-ing on its end. Only relatively recently has is been realized that a crescent-moon shaped fin is the most hydrodynamic shape and most efficient at creatingthrust. The reason lies in the way that swirling vortices (which are like

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mini-whirlpools) build up and are shed from the tips of the fin. The vorticesinteract with the fin, moving from side to side to push the fish forward. Thesame crescent-moon design is seen in the tails and wing shapes of fast-moving birds like swifts.

With these adaptations, the bluefin tuna can generate a huge amount ofthrust to push it through the water. Much of this energy can be transferred intoforward momentum because the bluefin tuna has several adaptations for reduc-ing drag through the water. The bluefin is flattened vertically so it can cutthough water. Its deep body, as well as being packed with muscle, acts as a keelfor balance. Its head is cone-shaped to punch through the water like a bullet.Their pectoral fins on either side of the body just behind the head are used togenerate lift to stop the fish from sinking, but these can be retracted into agroove to give further streamlining at high speeds. Even the eyes are flush tothe surface of the body to allow water to flow smoothly over the fish. Thanksto these adaptations to reduce drag, alongside the remarkable power that thebluefin’s muscles and tail generate, bluefin tuna can reach speeds of more than60 miles per hour (100 kilometers per hour) in short bursts. These fish areperfectly adapted for high-speed locomotion in water, allowing them to catchfast-moving prey and to escape their own predators.


The powerful and perfectly shaped tails of tuna are currently being exploredto see whether they can provide inspiration for a new form of marine propeller.It is still in the early stages of development, but the idea completely rewritesconventional wisdom on how to propel a vehicle through water. Rolls Royce,the company leading the research, is hoping the tuna can unlock the secretsof how to get the most propulsion out of tiny amounts of energy.

JET PROPULSION

In the 1930s, aviation was revolutionized by the invention of the jet engine.Until then, airplanes were driven forward by simple propellers that forced airbackward, generating forward thrust. Jet engines take this general principle andmagnify the force of the thrust produced. A propeller is used to suck in air to

the engine, where it is compressed andmixed with fuel and then ignited. Thisburning mixture of high-pressure air andfuel is ejected from the end of the engine,generating a lot more thrust than a propel-ler would have been capable of on itsown. Jet propulsion is now used in air-planes, rockets, spacecraft, and even landvehicles.


The longfin inshore squid, Loligo pealei. Aswith all squid, this species has a siphon(shown just below the eye) through which itcan force water to propel itself forward.[Richard Ellis / Photo Researchers, Inc.]

Jet propulsion has been responsible for the fastest speeds recorded byman-made machines. Certainly there is nothing in nature that can matchsuch velocities, although there are no organisms that need to travel so fast.High straight-line speed can be a hindrance when an individual might needto stop or corner at some point, but jet propulsion has indeed evolved innature and it as proved to be a highly success adaptation. Squid have anbuilt-in jet propulsion system that enables them to move at high speedthrough water, allowing them to hunt, evade predators, and even dance witheach other.

Squid are unusual-looking creatures. Different species of squid vary in sizefrom just 12 inches (30 cm) to 65 feet (20 m) in length. Their body is a muscu-lar foot called the mantle, which is the same as the body of other mollusks suchas snails and slugs. At the end of the mantle is a small head that consists of amouth and two very large eyes. Around the mouth are 10 tentacles, two ofwhich are longer than the others and have modified, clubbed tips for strikingprey and potential predators. The mantle has two fins that it beats in a ‘‘ripple’’effect that can propel it forward or backward at low speeds. When a squidneeds to travel much faster, though, it can deploy its jet propulsion systemhoused in the mantle.

The mantle is a hollow organ. Water can be drawn into the mantle cavitythrough an opening by the head. This is done by contracting certain musclesin the elastic mantle wall, which increases the volume of the mantle cavity,much like the expansion of our thoracic cavity when we breathe in. The squidcan then quickly contract other mantle wall muscles, squeezing out the waterinside the cavity. The opening by the head, through which water was drawnin, is now clamped shut by powerful muscles. As a result, the water beingsqueezed from the mantle can only escape through a thin funnel called thesiphon. The siphon is extremely mobile and can point in any direction, whichgives the squid a great deal of control over its jet propulsion and thereforethe directions in which it moves.

Squids can perform several of these bursts of jet propulsion in quick suc-cession, which is enough to escape prey or strike, at lightening speed, atunwitting prey. In this way, squid can travel up to 25 miles per hour throughwater and have even been known to hurl themselves from the water andthrough the air to escape predators. Even when traveling at these speeds, theyremain highly mobile. Recently, scientists recorded the giant squid, Taningiadanae, moving quickly under jet propulsion and flipping on the spot beforeshooting off in the opposite direction—not bad for an animal that is over6.5 feet (2 m) long.

Elsewhere in the oceans of the Southern hemisphere lives a completely dif-ferent type of organism that moves in a very similar way. Marine salps (of theclass Thaliacea) look exactly like jellyfish. They range in size from a few milli-meters to a few centimeters and have soft, gelatinous, transparent bodies.Despite their appearance, they are not jellyfish, but tunicates, one of the

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invertebrate chordates. Humans are chordates as well, so marine salps show allthe basic traits common to humans and related animals, although salps lack abackbone. These creatures are more closely related to us than to the jellyfishthat they so closely resemble.

Salps move about by jet propulsion. They draw water inside themselvesthrough one aperture and force it out of the other, thanks to contractions ofmuscles surrounding each opening. In addition to using it for movement,though, these creatures make use of the water passing through them by filter-ing the water and feeding off the algae left behind. The filter is a mucus bagthat is made up of sticky threads that create a fine mesh. It is sufficient to traptiny algae, but at the same time allows water to pass through to propelthemselves through the ocean.


It is fair to say that this is one area in which humans have far surpassed anyadaptation seen in nature. The next step for human engineers is to developpropulsion systems in a quest for greater and more efficient thrust. Engineersare already exploring beamed energy propulsion systems (essentially usinglasers) and ion propulsion (which to date has only been heard in episodes ofStar Trek). This leaves the humble squid somewhat far behind, but for thesedeep sea animals, their form of jet propulsion serves them fine. It allows themto strike with deadly speed, evade predators when attacked, and even take tothe skies, albeit briefly.

PARASITIC LOCOMOTION

All organisms undergo some form oflocomotion at some point in their lives.Animals, for the most part, move aboutunder their own steam. Many otherorganisms, though, move by being car-ried on currents of air or water. By thislatter method of locomotion even plants,which spend the vast majority of theirlives in one place, move about as seeds,often covering great distances. There isa further group of organisms, though,that could find it hard to move fromplace to place. Parasites living insideother organisms must move, eventually,to another host. Many parasites achieve

this by exiting the initial host, often as eggs or larvae, and waiting to beingested again by another unwitting individual. There are some parasites,


An electron micrograph of Rhinovirus-14, oneof the viruses responsible for the common cold.[Kenneth Eward / Photo Researchers, Inc.]

however, that have evolved the ability to move from host to host by directlymanipulating their host’s behavior.

We have all suffered from the common cold and are very familiar with thesymptoms that come with it. There are more than 100 different common coldviruses, collectively called rhinoviruses (‘‘rhino’’ meaning ‘‘nose’’). When thevirus is inhaled into the nose, individual virus cells attach themselves to a par-ticular part of the nasal cells called the ICAM-1 receptor. Once the virus hasdocked with the receptor on the outer cell membrane it can enter the cell itself.Inside the cell, the virus hijacks the host cell’s own machinery to replicate itselfmany times over. Eventually, the host cell will be filled with virus particles,at which point it dies and ruptures, releasing the new copies of the virus thatwill infect other host nasal cells and repeat the process.

After the initial infection with the virus, this process of viral replication goeson for about 8 to 12 hours before any symptoms are shown. It is estimated thatan infection can be triggered by just 1 to 30 virus particles, but these numbersgrow rapidly during the incubation period. Between 12 and 72 hours afterinfection, symptoms are displayed. Part of the immune response to viral infec-tion is the release of inflammatory mediators (which include histamine, kinins,interleukins, and prostaglandins) to protect against further infection. Theseinflammatory mediators dilate blood vessels and cause mucus glands to secretethe mucus so familiar to anyone who has had a cold.

Inflammatory mediators also trigger coughing and sneezing. What is strik-ing, though, is that the symptoms caused by the inflammatory mediators arenot necessary to effect a full recovery from infection. Some 25 percent ofpeople who are infected with the cold virus do not develop symptoms. Butthe action of coughing and sneezing is extremely helpful for the cold virus.A sneeze sends thousands of tiny droplets of saliva and mucus into the air. Eachone is packed with virus particles, the perfect way for the virus to travel fromone host to another.

The manipulation of the host by the virus gives it an excellent means tomove to the next host, but whether the virus is simply benefiting from ourhuman immune response or whether the virus has evolved this adaptationdirectly it is not clear. It doesn’t matter, though, as evolution has led to rhino-viruses being dispersed by the host sneezing. Other parasites, however, clearlyhave a much more direct effect on the host, changing its behavior to benefitonly the parasite and not the host at all.

Like many parasites, the parasitic flatworm Leucochloridium paradoxum hastwo dependent hosts. It must pass through a bird host and a snail host to com-plete its life-cycle. It will live in the bird host until, as eggs, the parasite willpass out of the bird in its droppings. The eggs will then hatch into tiny larvaecalled miracidia, which swim freely in water. From here they can enter the nexthost when a snail living near the pool or stream ingests the infected water.Once in the snail’s digestive system, the miracidia migrate to the main diges-tive gland, where they change into the next larval stage called the cercariae.

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These migrate through the snail’s body again and collect in long tubes calledsporocysts, which extend into the snail’s eye stalks. Several hundred cercariaecan be contained in one sporocyst.

The sporocyst in the snail’s eyestalk is visible through the snail’s translucentskin. What’s more, it will pulsate so that the overall effect is very much like ajuicy caterpillar crawling about in the vegetation. The effect is so realistic thatbirds will peck at the infected snail’s eye stalks thinking they are a tasty morsel,resulting in the parasite being ingested once more by its bird host. In additionto changing the appearance of the snail, the fluke also manipulates its behavior.No longer will the snail move around under the cover of vegetation as it wouldusually, but instead will crawl up the plants that ordinarily provide it shelterand sit on top of the leaves in plain view of bird predators, increasing thechance of the snail’s caterpillar-like eyestalks being spotted by a hungry bird.

A similar mind-control manipulation is seen with the rabies virus. The bullet-shaped rhabdovirus infects host cells much like any virus; it binds to the cellmembrane and then uses the host cells’ DNA replicating machinery to makecopies of itself. The virus will replicate in the muscle cells of its host, whichincludes most mammals, even humans. From there it will migrate to the nervesand eventually to the brain. The final stages of the infection sees the virusmigrate to the saliva ducts, tear ducts, sweat glands—anywhere that water isexcreted. It is here that the virus will get into the next host. To achieve this,the virus manipulates the host’s behavior. The infected animal will cease to bewary of other animals and will be prone to attack and bite anything that it comesacross. If it manages to bite another animal, the infected animal will pass on thevirus through its saliva. Thanks to its manipulation of another organism,the virus has a very reliable method for moving from one host to another.


It is unclear exactly how parasites manipulate their host’s behavior. It islikely that a chemical is produced by the parasite itself or causes one to be pro-duced by the host that alters the behavior-controlling part of the brain. It is atruly incredible adaptation to ensure that the parasite can move to the nexthost. Most of the attention focused on these parasites lies in treating the infec-tion rather than making use of their behavior-controlling adaptation. For thecold virus, there is a great deal of attention on treating the sneezing symptomsthat the virus elicits, so understanding how the virus affects humans is leadingto better treatments.

POLLINATION

For much of their lives, plants find themselves rooted to the ground andunable to move about. This is clearly not a huge problem for them. Plantsare enormously successful organisms that dominate the earth, so a sedentary


life is clearly no hindrance. However,there is a key part of their life-cycle whenplants do need to move from one place toanother. For those species that reproducesexually, the pollen from one flower musttravel to another, where it can enter theovary and fuse with an egg to create aseed from which a new plant will grow.Some plants rely on wind to dispersetheir pollen, but others have evolved aseries of ingenious adaptations to engagean animal to carry their pollen for them.

The advantage of employing an animalcourier to carry pollen from one plant toanother is that the plant does not haveto invest potentially huge amounts ofenergy to produce the vast numbers ofpollen grains that wind-pollinated plantsrelease. The strategy has its costs, though.To attract an animal to itself the plantmust offer some form of reward. The sim-plest solution to this problem is to offer upsome of the pollen itself. Pollen is nutri-tious, and many insects, birds, and mam-mals will readily eat it. The cyads, whichwere around at the time of the dinosaursand have changed little since, use thisapproach. Weevils that are attracted to the pollen spilling from the cyads’ hugecone-shaped, pollen-holding structure will get covered in pollen grains. Whenthey fly to another plant for the next feast pollen on their backs will be trans-ferred to the cyad’s sticky stigma, where it can fertilize an egg.

Other species offer pollen but restrict its access to just one courier species.Like all flowering plants, the pink gentian from southern Africa produces its pol-len in specialized organs called anthers. However, the gentian hides its polleninside its anthers, rather than growing it on the outside for any animal to getat. The only way for the pollen to escape is through a tiny hole at the top, andonly one group of bee has evolved to get at it. African carpenter bees cling tothe anthers and buzz their wings together at a precise frequency. This providesexactly the right vibrations to shake the pollen from the hole in the anthers,which the bee will gather up and store in its specialized carrying baskets on itslegs. Again, as a foraging bee travels from plant to plant in search of food, someof the pollen is transferred between plants, allowing fertilization to take place.

Of course, a common reward that plants offer their couriers is the sugaryliquid nectar. The flowers of many plants are shaped so that to get at the nectar

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The flower of the wild orchid, Ophrys scolopax,mimics the shape, color, and smell of the femalelong-horned bee (Eucera longicornis). [PerennouNuridsany / Photo Researchers, Inc.]

hidden deep within the nectaries of theflower, the insect or bird must positiontheir bodies in a certain way. This posi-tion allows the animal to get its rewardbut also requires it to brush past thepollen-heavy anthers and sticky stigma,the female organ of plants. In additionto having a particular shape, many spe-cies grow flowers that release attractivescents and that are colored to attract cer-tain insects. Furthermore, as manyinsects can see ultraviolet (UV) light,flowers invest in UV reflecting patterns.Often these markings act as a ‘‘landingstrip,’’ directing the insect where to landand how to get at the nectar. The moun-tain laurel from North America and theSpanish Iris from northern Spain,among many others, use markings todirect their pollinators.

Not all plants offer an honest rewardfor the services of their pollinators. Sexsells just as well as food, and many plantsoffer insects what they perceive to be awilling mate. The orchids are especiallywell adapted to these seemingly under-hand tactics. The mirror orchid growsin regions west of the Mediterranean inEurope. Its flowers are a metallicviolet-blue color with a yellow border

trimmed with red hairs. On either side there are two smaller oval shapes thatlook like wings, giving an overall effect of a bee. To be more specific, the effectis of a female bee. The illusion is completed by the plant releasing a scent thatmimics the pheromones released by sexually receptive females. The wholeappearance is enough to fool a male, which will try to grasp the flower as ifhe were mating with a real female. As he tries to copulate, a curved column atthe top of the flower swings down and glues a packet of pollen, called a pol-linia, to the male’s head. This curved structure has both male and femaleorgans so that as it swings down it picks up any pollen that has been depositedon the male by a nearby plant.

Many orchids use this approach, which has led to the evolution of manyingeniously designed flowers. In some species, such as the yellow bee orchid,hairs on the surface of the flower trick a male pollinator into thinking thatthe female he is trying to mate with is sitting on her perch with her head


Amale long-horned bee is fooled by the orchidmimic and attempts to mate. As it does so, theorchid deposits a pollen-containing packetcalled a pollinia on its head. The bee will thentransfer the pollen as it attempts to mate withother orchids. [Perennou Nuridsany / PhotoResearchers, Inc.]

pointing downward. When he triggers the mechanism to deposit the pollinia,the packet of pollen is deposited on the bee’s abdomen, rather than itshead. Orchids are therefore described as being either ‘‘front loaders’’ or‘‘back-loaders.’’ The result is that two species of orchid can share a pollinator.One species is fertilized by depositing pollen on the abdomen, and the otherhas its pollen carried on the bee’s head.

There are many specialized adaptations that in one way or another coerce ananimal, typically an insect, to carry a plant’s pollen for it. Each one is perfectlyadapted for the plant in question and means that even stationery organisms canmove about, albeit by recruiting the locomotive talents of other species to do so.


The success of many of the crops grown by humans is dependent on theirpollination by insects. Disease or adverse weather conditions can devastatepopulations of pollinators like the honey bee, which in turn can have devastat-ing effects on crop yields. This is why there is a great deal of interest in study-ing the pollinating behaviors of certain key insects. Agriculturalists are nowbeginning to realize that suitable habitats for their crop pollinators need tobe provided alongside crop fields to ensure that plants are fertilized so seedsand fruits can be produced.

BACTERIAL FLAGELLUM

All organisms show some form oflocomotion. Animals show the greatestrange of movements, but not one speciesis capable of generating constant thrust,not even the hummingbird. At somepoint in the movement of a wing or legthere is a reduction in thrust as it returnsto its starting point. Some animals comeclose to generating continuous thrust—the undulating bodies of fish, snakes,and eels, for example—but there are stillinefficiencies in these movements.Humans, on the other hand haveinvented the wheel, which can spin freelyand so can produce constant forwardthrust, be it in cars or as the propeller ofan airplane or boat. It was thought thata free-spinning wheel cannot evolve inanimals, as there are too many limitingfactors. You can get close by whirling

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An electron cryotomography scan of a bacteriumflagellum shown from different views. Bacteriaflagella are the only wheel-like, free-spinningstructures known to have evolved. [GavinMurphy / Nature / Photo Researchers, Inc.]

your arm around in a circle, but your shoulder will never spin freely in itssocket because the muscles, tendons, and ligaments would soon get twisted.Without being able to evolve a wheel, animals are doomed to roam withimperfect movement.

Remarkably, though, the wheel has evolved—not in animals, but in bacteria.This is a truly staggering adaptation and quite possibly the most complex andelegant one on this planet. Until very recently, it was deemed so complex thatquestions were asked about whether it could have evolved by natural selectionat all.

As with human designers, bacteria put their wheel to use to move around.Attached to one end of the bacteria’s body is a free-spinning wheel that is inturn linked to a long, tail-like filament called the flagellum. Driven by a tinymotor, the flagellum can spin like a propeller to drive the bacterium throughwater.

There are three elements to the flagellum. The motor that drives the flagel-lum is called the basal body, which is embedded in the cell wall of the bacte-rium. Within the basal body is a series of three rings, which are about20 nanometers in diameter. One ring sits within the inner membrane, one sitswithin the cell wall itself, and the third ring sits within the outer membrane.Within these rings is a thin rod that is free to spin through 360 degrees.Attached to the rod is the second element to the device, called the hook. It con-nects the basal body with the third element: the filament, which is a thin,whippy structure made from a protein called flagellin. It is about 5 to15 micrometers (5,000 to 15,000 nanometers) long. As the rod within the basalbody spins, the filament spins too and propels the bacteria through the water.In total, about 40 proteins self assemble to create this sophisticated piece ofnatural engineering.

The typical source of energy in living organisms is the energy-rich moleculecalled adenosine tri-phosphate (ATP), and so one might assume that this is thefuel that drives this bacterial motor. However, although ATP is used in bacte-ria to power other functions (including the building of its flagellum), it is notused to power the basal body motor. Instead, the motor is powered by electri-cally charged sodium ions (in some species) or electrically charged hydrogenions (in others) flowing across the cell wall. The bacterial flagellum is anelectric motor! This is a highly efficient power source. Nearly 100 percent ofthe energy stored within the sodium and hydrogen ions crossing the cell mem-brane is transferred to the spinning filament, which allows the filament to spinat up to 100 times a second. This can drive a bacterium forward at a speed ofabout 25 micrometers (10 bacterial body lengths) a second. In relation to bodysize, that is about twice as fast as a human can run at full speed.

In all bacteria that have a flagellum, the rod (and therefore filament) spinsmost of the time in a counter-clockwise direction. But the direction can bereversed occasionally, causing the bacterium to do a somersault so it faces theopposite direction. Switching back to a counter-clockwise spin, the bacterium


can then swim off in a different direction. This behavior, called tumbling, isvery important for an individual bacteria to steer. Bacteria have tiny sensingmolecules that can detect whether they are moving toward a food supply orsomething poisonous. Bacteria will therefore adjust their direction so theytravel toward food and away from toxins. Their sensors interact directly withthe tiny molecular switch that controls the direction the rod rotates. In toxicenvironments bacteria tumble more frequently to attempt to find a way outof danger. This behavior of detecting and responding to chemical stimuli inthe environment is called chemotaxis.

A spinning flagellum is an excellent way for a bacterium to get about,although there are times in their lives when bacteria cease swimming and clus-ter together to form a community of bacteria called a biofilm. Biofilms formand adhere to surfaces (a good example is the bacteria that make up dentalplaque on teeth) or float to the surface of water. They are typically very resist-ant to host defenses such as antibiotics and so they help bacteria survive inharsh environments when individuals living on their own might easily bekilled. When clustering in this way, the last thing bacteria would want arespinning flagella, which could break up the biofilm.

When bacteria switch from a free-swimming lifestyle to a more sessile wayof life they disengage their flagellum. One might expect the flagellum to stopspinning somehow, but this is not the case. Instead, the rod keeps spinning,but the link between the rod and filament is disengaged. Bacteria have evolveda microscopic clutch for their motors! The advantage of having a clutch is thatthe bacteria can easily return to their free-swimming way of life simply bydropping the clutch and reengaging the filament with the motor. The clutchhas been identified as a protein called EpsE. When the bacteria wants to stopswimming it produces this one protein that disengages the rod from thefilament. It does this by changing the shape of the basal body. When it wantsto swim again, the EpsE protein is broken down, allowing the filament toreengage with the spinning rod.


There is a great deal of interest in designing and building nano-robotsdriven by microscopic engines like the basal body motor. These can be usedfor a number of applications, such as delivering drugs and repairing organsfrom within the body. By studying the bacterial flagellum, which self assem-bles, nanotechnologists are gaining insights into how they might produceengines on their own tiny, man-made machines.

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4

MATERIALS

MATERIALS—HUMAN INVENTION

Many species of animal make use of tools to aid their survival, but humans arethe undoubted masters. Manual dexterity and a keen, problem-solving brainhave allowed us to design and build a cornucopia of gadgets that have assistedour quest for survival. Our human ancestors are likely to have discovered thefirst basic tools by chance. Certainly, though, their inquisitive brain wouldhave helped discover the range of uses such tools could be put to. Today’shigher apes show a similar tendency to use tools when confronted with aproblem that cannot easily be solved using their hands.

It is uncertain when our human ancestors would have taken a more proac-tive approach to tool making. Our brain is certainly capable of addressing acertain problem and imagining what tool would help solve it. From there, wecan design the tool that has formed in our mind. Our ancestors will have hadthis same ability. There has even been the suggestion made recently that itwas the accidental discovery of tools that kick-started the evolution of thehuman intellect. However the use of tools arose in human history, one of thelimiting factors in tool making is the materials that are available.

The earliest tools were made from wood, bone, or stone. The first stonetools were made some 2.5 million years ago. Even this far back our ancestorswere carefully choosing their materials to make the right tool. The first toolsmade by Homo habilis were made from stones of volcanic rock worn smoothby the waters of creeks and rivers. These cobbles were struck by other stonesto flake off pieces of stone to create a hand-held tool with a sharp edge but asmooth handle. These simple tools could have been used to butcher animalsso humans, with weak jaws and teeth, could get to the energy-rich flesh within.

Stone tools have the benefit of remaining in the archaeological record so wecan see the type of materials used by early man, but we assume that other mate-rials were used as well. Wood, bone, and horn have varying toughness, buteach can be easily shaped and fashioned into a tool. Leather and furs fromthe skins of animals could have been used for clothing and housing materials.Sinews from animals would have been used for making tight-binding cordage,likewise, the fibers and bark of plants could have been used for similarpurposes.

These natural materials used by early humans were, and still are, extremelyversatile media to work with. Humans still use them to this day and in someinstances they remain superior to man-made materials. Of course, syntheticmaterials can be made from naturally occurring ‘‘ingredients.’’ Copper occursnaturally as a metal and is readily shaped, being a soft metal. This form ofmetal was used some 10,000 years ago, but it took a further 3,000 years beforecopper was extracted from its ore (metal contained in rock). This was quite aleap forward in producing materials. For nearly half a million years prior tothis moment fire had been used only for cooking and warmth.

Around 3500 BC humans discovered that copper could be made stronger if itwere melted together with tin and then allowed to cool, making the first alloy(a mixture of two metals). The resulting bronze was used for making a widerange of tools, including weaponry and farming tools. Further alloys werebeing discovered, though, and in 900 BC brass was discovered by mixing copperwith zinc. Two thousand years after discovering how to make bronze,advanced fire-making technologies using kilns allowed hotter fires to be main-tained, which allowed iron to be extracted from its ore. Although it is a weakermetal than bronze, wrought iron was a preferred material because it kept asharper edge, making it useful for weaponry. Iron can be made stronger,though. It was soon discovered that iron mixed with small amounts of carboncreate steel, a very strong and workable metal indeed.

It is only in the last 150 years that we have begun to move away from adependence on metals and natural materials like wood, although these materi-als are still very important. Plastics are man-made materials that are light-weight, moldable, and noncorrosive. All plastics can be heated and shaped,which means they have a huge range of applications. Typically, they are poly-mers. This means that their chemical structure is made from a single moleculerepeated over and over again in chains or sheets. The way the chains interactwith each other gives the particular plastic its physical properties.

There are a number of naturally occurring polymers, and indeed the firstman-made plastic produced in 1862 (Parkesine—named for its inventorAlexander Parkes) was derived from cellulose that is found in plants. Parkesinedisplayed the classic plastic trait of being readily moldable when heated. Fromthis point, there followed a whole range of man-made plastics. Celluloidappeared in the nineteenth century, first as a replacement for ivory in billiardballs and then in its more familiar guise as photographic film for motion


pictures. It wasn’t until the invention of Bakelite in the early twentieth century,though, that plastics really took off.

Bakelite was the first entirely synthetic plastic to be produced. It is producedfirst as a liquid, which molds to whatever container it is poured into and setshard as a resin. Unlike other plastics, it cannot be melted down again to bereused. In liquid form, bakelite can be added to more or less any material tostrengthen it. During the Second World War the U.S. government used it inmany instances in armor and weaponry as a replacement for steel. For manyyears after, it could be found in most household objects because it does notbreak, fade, crease, or crack under a wide range of extreme conditions.

The list of successful plastics is huge and include familiar names such asnylon, cellophane, PVC, teflon (noted for its ability to allow nothing to stickto it), polyethylene, velcro (plastics shaped into complementary loops andhooks), and perspex. Each of these has a fundamental impact on nearly everyaspect of our lives and has enabled huge leaps forward in cutting-edge fieldslike medicine, space exploration, and the military. The family of plastics con-tains a hugely versatile and varied range of materials, and there is great scopeto produce more. Many are carbon-based, but the key to their properties liesin the other elements that hang from the carbon ‘‘skeleton.’’ By tweaking thebasic chemical building blocks of carbon a whole range of properties can begenerated.

Similar to plastics are synthetic materials like kevlar. These are importantmaterials because they have a much greater strength-to-weight ratio than met-als like steel, which means they can be used in structures that need to be strongyet light. Kevlar, or poly-paraphenylene terephthalamide to give its chemicalname, is made from long molecular polymer chains that bind together verytightly. Some polymers have weak interactions between the long chains, whichgives them flexibility and moldability. The tight binding between kevlar poly-mers gives the material overall strength, albeit with flexibility as well.

Kevlar is used in ropes and cables, canoes, tire walls, drum heads, woodwindreeds, electricity generators, fiber optics, in brakes, and for many constructionpurposes. Probably its most recognized use, though, is in body armor. Sheetsof kevlar in body armor and helmets can ‘‘catch’’ a bullet and slow it suffi-ciently to prevent serious injury in the wearer. It is thought that hundreds ofsoldiers’ lives are owed to the bullet-stopping properties of this remarkablematerial.

Although humans still rely on many naturally occurring materials, there aremany synthetic materials that have improved on what we have harvested fromnature. Man-made materials have the benefit of being produced in well-controlled environments, which means that their microscopic structures canbe put together with minimal flaws and weaknesses. This is crucial for produc-ing steel, say, which is going to be used to build skyscrapers hundreds of feet inthe air, as the engineers need to know the exact properties of the material theyare working with. New materials are constantly being produced, but much of

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the inspiration comes from materials found in nature that continue to outper-form anything produced by humankind.

SILK

Humans have developed amyriad of materials to build everstronger and taller structures. Sim-ilarly, the natural world aboundswith materials that are put to gooduse in the construction of impres-sive structures. Perhaps the mostremarkable of these is silk, whichcan be spun and used by insects ina numerous ways.

Silk has been valued by humansfor centuries because of its uniqueproperties, but the ability to pro-duce silk is restricted to certaininsects and arachnids. Silk is a pro-

tein with a microscopically complex structure, and it is secreted from theglands of silk-producing animals as viscous liquid. This liquid is directed andmanipulated with specialized organs located at the opening to the silk gland.For many years it was not understood how this liquid became the solid fiberswe are familiar with. Some scientists reasoned that contact with air changedthe silk from a liquid into a solid, but it’s now evident that tension causes thischange. The simple act of pulling the liquid silk tight hardens it into a solid,flexible material.

The microscopic structure of silk varies considerably from species to spe-cies, but the basic structure is a long chain of amino acids (the buildingblocks of proteins) that are arranged into loose spirals and rigid sheets. Thesheets are arranged together to form protein crystals, similar in appearanceto a section of corrugated iron. These crystalline regions are separated bytangles of loose protein chains, and it is the combined properties of thesehard areas and more elastic regions that bestow silk with it extraordinarycharacteristics.

Silk is very strong indeed, much more so than other biological materialssuch as bone or tendon, and it is twice as elastic as nylon. In terms of tensilestrength, spider silk is about half as strong as steel, but it much less dense.The tensile strength-to-density ratio of silk is five times that of steel and ison a par with super strong fibers such as Kevlar. It has been said that astrand of spider silk the same thickness as a pencil could stop a jumbo jet inflight. Bold claims aside, silk is undoubtedly a remarkable material and it hasbeen instrumental in the success of several species that can make and use it.


A scanning electron micrograph of spider silk show-ing the different type of strands that a spider iscapable of producing. [Mona Lisa Production /Photo Researchers, Inc.]

Of all the invertebrates that produce and use silk it is the spiders thatemploy it most widely. They not only produce a bewildering array of websto catch prey, but they also use it for drag lines to anchor them safely whenthey are climbing; to fly through the air on long, fine threads that catch thewind; and as wrappings for disabling and storing their prey. Thanks to itsmolecular structure, it is also waterproof, which means that it is an excellentmaterial for spiders and insects to wrap their eggs and developing youngto protect them from the elements, both from getting too wet and fromdrying out.

Although the spiders are the undisputed masters at using silk, some otherarthropods are also very accomplished when it comes to producing and usingthe material. Pseudoscorpions produce silk from their mouthparts, and theyuse it to produce tiny silken igloos in which to molt, lay eggs, and see out coldweather. The larvae of bees, ants, wasps, and some butterflies and mothssecrete a cocoon of silk just before they pupate. The silk produced by bees,ants, and wasps consists of multiple helices wound around each to produce afiber that is very tough and with quite different properties compared to the silkthat is produced commercially from the silk moth (Bombyx mori). The larvae ofsome fly species also produce silk, and the black fly larva use silk to anchorthemselves in fast flowing water. They secrete a small pad of silk onto a suit-able rock and attach themselves to this secure anchor using small hooks ontheir rear end.

In many instances, structures built using silk are left exposed to the ele-ments over quite a long period of time. Silk structures can be used for days,weeks, and even years, which exposes the material and the structure to attackfrom microbes and other pathogens that could be harmful to the insect orspider that constructed the web in the first place. Some spiders live in envi-ronments heavy with bacterial and fungal infection. Funnel web spiders thattunnel through the soil are exposed to many pathogens, as are cave spidersthat come into contact with thick fungal growth on the walls of their warm,humid caves. To protect themselves from these pathogens, they have evolvedan antimicrobial silk that allows them to live in near-sterile conditions. Thesilk is also very helpful for spinning an antiseptic cocoon for spider eggs,offering great protection against disease when the young are at their mostvulnerable.

It is not clear how this antimicrobial property is achieved. It does not appearthat spiders secrete an antibiotic fluid that coats the silk, but rather that silkitself is resistant to attack by bacteria and fungi thanks to its molecular struc-ture. It seems that this resistance comes from the presence of certain small pro-teins that make up the silk.

Each of silk’s many uses requires it to have different physical properties.The exact molecular structure of the silk protein produced by a particular spe-cies determines these properties. Having more loose protein chains in thestructure will make silk more flexible and elastic. With a greater proportion

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of stiff protein sheets, the material will be much stronger or more waterproof.There are even molecules that can be added to the silk that can make it stickyfor catching prey. What is more remarkable is that one individual can oftenproduce different types of silk at will. There is no doubting the enormous ben-efit of being able to produce silk. In the species that produce it silk is used forso many aspects of life that it can be considered the single most importantadaptation that they have evolved, enabling them to exploit a range of uniqueevolutionary niches.


The antiseptic properties of silk have been alluded to in literature for severalcenturies. Even Shakespeare mentions it in A Midsummer’s Night Dream.Scientists are only now beginning to fully explore this folklore, but the hopeis that the strength, flexibility, and sterility of silk can support several medicaluses, from bandages to futuristic stitches that hold transplanted organs inplace, or as scaffolds to allow grafts to knit together.

The main area of interest, though, is in making use of silk’s remarkableproperties of strength. It can stretch by up to 40 percent of its length andcan absorb 100 times more energy than steel before breaking. Research isbeing carried out on the molecular structure of silk. It seems that silk is madeup of distinct regions of alternating flat, rigid sheets of protein and amorphous‘‘blobs’’ of protein, which can curl up on themselves and stretch out like aspring. The relative frequency of each region gives different silk its properties.Research is looking to recreate these silk regions and to put them together indifferent ways for different purposes. One of these purposes is to producebulletproof vests that are lighter and tougher than kevlar.

BONE

Almost invariably, stable structures are built around a solid scaffold. Formost vertebrates, this scaffold is a skeleton of bone—though some vertebrates,such as sharks, have skeletons of cartilage. Like all good structural materials,bone is strong, hard, and flexible. It grows with the body and can even repairitself if it breaks. What’s more, in several species it has evolved in highlyspecialized ways, which has allowed these organisms to exploit new nichesand a unique way of life.

The basic structure of bone is quite simple. It is made from a repeatingmatrix of collagen fibers, the springy molecule that gives skin its plumpness,which is strengthened by various hard minerals. Collagen, which makes upabout 30 to 40 percent of the weight of bone, is itself a strong material. Mostof bone’s strength, though, comes from hard minerals that are built up aroundthe collagen matrix. These minerals are typically calcium phosphates, the mostcommon of which is a mineral called hydroxyapatite.


The collagen matrix and cal-cium salts work well together togive bone its strength. Collagenhas very high tensile strength,which means that it can withstandbeing pulled apart. The calciumsalts, conversely, have very highcompressional strength, whichmeans that bone can withstandhigh weight loading. This lattercapability is very important whenyou consider the weight of animalslike elephants and the pressuretheir own bulk must place on theirleg bones. Unfortunately, how-ever, bone does have one weak-ness—it has a very low torsionalstrength. Most fractures are theresult of the bone being twisted.

The strength of bone is not due simply to a random mixture of collagen andminerals. It is a highly structured material, and it is this structure that confersits toughness. The outer layer of bone is a thin but tough fibrous layer of tissuecalled the periosteum, which serves to protect the bone and acts as an attach-ment point to the muscles and tendons which join to it. Within the periosteumis a thick layer called compact bone. This, as its name suggests, is hard andcompact. It is the periosteum that gives bone its rigidity and resistance tobending. Compact bone is highly structured, being made up of a series ofconcentric layers of the calcified collagen matrix.

Bone that supports a limb has two distinct regions that have slightly differ-ent structures. The area at each end of the bone (where the bone makes a jointwith another bone) is called the epiphysis. The long section between the endsis called the diaphysis. Both are covered with compact bone, although thediaphysis generally has a thicker layer to protect it from direct blows to the sideof the limb. Within the compact bone layer of the diaphysis is a cavity filledwith yellow bone marrow. The cavity of the epiphysis, however, is filled witha different type of bone called spongy bone. Spongy bone is made up of colla-gen and calcium salts, as with all bone, but they are arranged as a very loose,air-filled network. This gives the bone in the epiphysis more elasticity, whichallows it to cushion the weight that is borne on the joints.

The gaps between the strands of spongy bone is filled with red marrow,which is involved in producing red and white blood cells. The yellow marrowthat fills the cavity inside the diaphysis part of the bone is involved with fatstorage. The fact that bone is not solid all the way through is significantbecause it saves weight. Bones are strong, but at the same time light. This is

MATERIALS 85

A light micrograph through a section of bone show-ing Haversian canals and the concentric rings oflamellae around them. Haversian canals carry bloodvessels, lymph vessels, and nerves. Lamellae aremade from compacted collagen fibers and mineralsproduced by bone-forming cells called osteoblasts.[Steve Gschmeissner / Photo Researchers, Inc.]

best seen in birds, whose bones are hollow with very few strengthening sup-ports to keep some rigidity. This weight-saving adaptation has allowed themto conquer the skies. If they had the bone structure of humans or other mam-mals they simply would not be able to take off under their own weight.

It is not just marrow that runs through bone. Bone cells called osteoblastsgrow within the hard material, producing more collagen and calcium salts.These cells are supported by blood vessels that run through narrow tubes,called Haversian canals, which permeate even compact bone. Even when ananimal has reached its full size, osteoblasts continue to produce new bone,albeit at a much slower rate than when an animal is growing. This is balancedby the activity of cells called osteoclasts, which break down bone material.Bones are constantly being recycled and rebuilt to keep them strong.

Bones being able to grow is a crucial adaptation, which allows young ani-mals to develop into adults. This is very different from invertebrates, whichneed to shed their outer skeleton before they can increase in size. What’s more,the mechanisms that allow for bone to grow also allow bone to heal itself.When a bone is broken, osteoblast cells are produced in great numbers fromthe periosteum. This allows a collagen matrix to be rapidly produced to bridgethe gap between the two broken ends. More slowly, calcium salts are laid downaround the collagen framework to rebuild the compact bone.


For such a lightweight, porous material, bone is remarkably strong. Poundfor pound it is a stronger material than steel. It is also much more versatilegiven that it remains strong despite being filled with gaps. The basic structureof bone has been well-known for many years, but still there are discoveriesbeing made. It is now recognized that much of bone’s strength comes fromthe atomic level. At this miniscule scale, scientists have observed that collagenmolecules and tiny hydroxyapatite crystals are stacked on top of each other,which allows them to bond together very tightly. This structure even allowstiny cracks to appear that, rather than weakening the structure, actually makeit much stronger. These discoveries are helping nano-engineers to designnew strong, but lightweight materials that will take us beyond steel and carbonfiber as our basic, man-made building blocks.

CHITIN

Arthropods are the most diverse group of organisms on earth and the mostnumerous of all the animals. This is a group that contains the insects and thecrustaceans, each of which have the same basic design that has proved to be avery successful template for survival. Unlike mammals whose frame is sup-ported by an internal skeleton of bone, arthropods are supported by an exter-nal skeleton of a substance called chitin. Although this may sound strange to


us, there is one important benefit ofthis design. In addition to provid-ing a rigid structure to allow move-ment, an external skeleton can forma protective outer layer of armorplating.

Arthropods are indeed well-armored creatures. The thick shellsof crabs are a very good example,but many insects are also well pro-tected thanks to a hard exoskeleton.Both the crab’s shell and insects’exoskeletons are made from a versa-tile material called chitin. Likebone, chitin can be very strong andprovides important protection forthe body. Unlike bone, chitin isextremely light and can be very flex-ible, allowing insects to be very fastmoving. Often these two adapta-tions—hardness and flexibility—are combined to produce agile yetwell-protected individuals.

This versatility of chitin is due to its molecular structure. Unlike similar mate-rials like keratin, a protein, chitin is actually a carbohydrate. And unusually for anaturally occurring material, it is a polymer—that is, a long, endlessly repeatingchain of one basic molecule. There are many man-made polymers, notably plas-tics, and these have the property of being firm but flexible. Chitin is no different.The basic polymer structure can be strengthened by the addition of certainother materials, such as calcium carbonate in the case of a crab’s shell. For themost part, though, chitin’s different properties come from how the material isshaped and laid down in a growing organism.

Chitin is a very adaptive material. The secret of its success lies in how it canbe deposited in layers to achieve whatever properties are required for the job.Depending on how thick it is, the material can be either very rigid or very flex-ible. Typically, a thick layer covers the body of arthropods in a structure wewould recognize as shell. The chitin shells of crabs are very strong and rigid,offering protection from predators and from the high pressures of the deepocean. This rigidity would be no good for the jointed limbs of crabs or insects,and yet chitin is used for these body parts too. For these organs, then, chitin islaid down in very thin layers that allow the joints to move freely and quickly.

The versatility of chitin doesn’t end with it being either hard or flexible.It can form a waterproof layer that is impermeable not only to water but togases as well. This is a very useful property for the outer armor of an insect

MATERIALS 87

A scanning electron micrograph of a butterfly wingscale made from chitin. [Cheryl Power/PhotoResearchers, Inc.]

that, like our skin, needs to keep water out. In other structures, such as in thegills of insect larvae or in crabs, chitin can do the opposite and let water andgases (like oxygen) pass through it.

A further important property of chitin is that it can do all these things andyet it remains a very moldable material. This means that arthropods, andinsects in particular, have been able to evolve a remarkable range of shapesand sizes without compromising their successful basic body design, which pro-tects the organs and gives support for muscles and other tissues. Insects havetherefore been free to evolve unique body shapes that can be useful for addi-tional defense, such as in growing spines or additional armor plating or foradaptations like flight, camouflage, and communication.

There is no doubt that chitin is a very important material for arthropods,being used for the body armor, limb joints, and wings. However, it is also thematerial used for many of the specialized organs in arthropods. In a highly spe-cialized form it makes the lenses that in turn make up the compound eyes ofinsects. It is also used for other sense organs that are involved in taste and smell.It can also be molded into the fine, iridescent scales that reflect light in such away as to give insects like butterflies their incredibly vibrant and metallic color.

For insects one of the most important uses of chitin is to protect their youngwhen they are just eggs. Chitin allows adult insects to have evolved into manyweird and wonderful shapes, and their eggs are no different. The eggs of eachspecies of insect has its own unique design that is perfectly adapted to the envi-ronment in which they are laid. For example, the eggs of water bugs, which arelaid in water, have a shell with an intricate microstructure called a plastron,which allows oxygen, but not water, to pass through it to enable the developingembryo to breathe but not drown. This is achieved by folding chitin into aseries of grooves and chambers that allows air dissolved in the water to accu-mulate, but not the water itself. Butterflies, on the other hand, lay their eggson dry land and in the open. Their eggs are therefore toughened by bands ofchitin wrapped around them, giving them the appearance of hand grenades.These eggs are therefore very tough and can withstand very dry conditionswithout desiccating.


Chitin is very similar in structure and properties to another natural carbohy-drate polymer, cellulose. Cellulose is a key material used for making plant cellwalls, and it is this that gives plants like trees their tremendous strength andflexibility. There is little to distinguish these two polymers on the molecularlevel. A few alternative atoms hanging off the basic molecular structure hereand there are the only differences. Scientists have exploited this principle andexperimented with changing a few of these atoms of both chitin and cellulose.The results have been very fruitful. Chemically altered chitin has been used forbandages, burn dressings, food additives, drug capsules, and even cosmetics.


Chitin is also finding its way into surgical medicine. Because chitin is biode-gradable (it breaks down easily in water if not maintained or protected bythe wax that typically covers it in nature) it can therefore be used for internalsutures for organs that can simply dissolve weeks or months after anoperation.

FEATHERS

With between 8,000 and 10,000 spe-cies known today, birds represent a verysuccessful class of animal. They all sharecommon features that have allowedsuch a diverse group to have evolved.Although some species have lost theability, most birds are able to fly, whichhas allowed them to exploit habitatsand ways of life unavailable to land-bound animals. There are several keyadaptations that have led to the evolu-tion of flight. Various weight-savingadaptations such as hollow bones meanthat less energy is required for an indi-vidual to get off the ground. To get offthe ground, the evolution of wings fromhand and finger bones has given birds ameans to generate the lift and thrustessential for flight. But perhaps the most significant adaptation is the evolutionof the feather. This versatile material is crucial for many behaviors in birds andhas been the key to their evolutionary success.

Feathers grow from follicles embedded in a bird’s epidermis, much like hairgrowing from follicles in humans. They are arranged in rows so that the feath-ers overlap to provide the whole body with protection and insulation. Likehair, feathers are made up of the fibrous protein keratin, which fills the cellsgrowing at the base of the feather. As more cells grow behind them, thekeratin-filled cells will eventually die to leave a tough protein skeleton thatconstitutes a feather. Exactly how the cells grow and how the keratin is laiddown determines what kind of feather is produced.

There are several types of feather for different purposes. Quill feathers arelong and thin and are found only on the tail and wings. Contour feathers aremuch shorter and cover the body, filling the gaps between the quill feathers.Down feathers, or filoplumes, lie beneath the contour feathers. These are fluffyand almost hair like and are important for insulation. All feathers have thesame basic structure, though. Running along the ‘‘spine’’ of the feather is astiff, narrow cylinder called the rachis. On each side of the rachis is a row of

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A scanning electron micrograph of a feather of theEastern bluebird (Sialia sialis). These feathers showthe remarkable microstructure that reflect bluelight, giving the feathers a blue color. [EdwardKinsman / Photo Researchers, Inc.]

barbs that themselves support even smaller barbules. On one side of each bar-bule is a row of hooks. These fit into a groove on the neighboring barbule sothey sit together tightly.

Interlocking barbules are an important feature of a feather. They maintainthe integrity of the feather without the need for producing one solid structure,which allows for the feathers over the bird to create a complete, but light-weight, covering that is essential for flight and for warmth. To align the bar-bules of the feathers, a bird must regularly preen its feathers. If you find adiscarded feather you can see this effect. First, ruffle the feather so there aregaps in the vanes on either side of the rachis. Then pinch the rachis and runyour fingers gently from the base to the tip. The barbules will realign like azip, and the feather will be restored to its original shape. There are more bar-bules on the quill feathers because the feather shape is essential for flight. Con-tour and down feathers have fewer barbules because there is less need for themto maintain a continuous flat surface. The integrity of feathers gives the wing alight but rigid structure that allows air to flow over it to generate the lift andthrust needed for flight.

Feathers are extremely important in restricting heat loss from the body.The down feathers will form a loose network of fibers in which air is trapped.The contour feathers over the top will help trap the air and create a warm,insulating layer. Even a thin layer of feathers offers excellent insulation.Emperor penguins living in the Antarctic have to cope with temperatures aslow as −22°F (−30°C) and wind speeds of up to 125 miles (201 km) per hour,and yet they still maintain a body temperature of 100.4°F (38°C). In part thisis thanks to a layer of blubber beneath their skin, but it is also down to theirfeathers which are small and densely packed with a woolly down layer closeto the skin. Penguin feathers are also good at shedding water as they leavethe ocean after hunting for food. Indeed, all birds’ feathers are waterproofthanks to a covering of oil that is secreted from an oil gland near the bird’stail. This is spread over the whole body using the beak when the bird preensitself.

In addition to being essential for insulation and for flight, feathers play animportant role in attracting mates or staying camouflaged thanks to theircolor. For most birds, the color of their feathers are produced by a mixture ofthree types of pigment that are embedded in a bird’s feather cells as they grow.Melanins produce yellow, red-brown, dark brown, and black colors. Carote-noids are responsible for brighter yellows, oranges, and reds. Porphyrins arethe least common group of pigments and produce greens, reds, and pinks.There is a fourth group of pigments called psittacofulvins that produce thedeeps reds and oranges of parrots (the name means ‘‘parrot-pigment’’). Psitta-cofulvins differ from the more common carotenoids that have to be gainedfrom the bird’s diet. The parrot pigments can be produced by the parrotsdirectly and are not dependent on diet, which means they remain brilliantlycolored no matter what they eat.


Although many birds have blue-colored feathers, no blue pigment exists inbirds. The dazzling display of birds like peacocks come from the shape andstructure of the feathers themselves. The crystal structure of the feathersreflect and bend light in such a way as to produce a blue color. Greens, yellows,and reds can be produced in the same way. On the edge of the tiny barbules ofthese feathers there is a crystal lattice of melanin and keratin rods that gives thebarbule a unique two-dimensional structure, which reflects and bends light in acertain way to produce color. The color produced depends on the number andspacing of these protein rods. These feather crystals are known as photoniccrystals because of their color-producing properties.

The colors and patterns of bird feathers are certainly important for matingdisplays and in settling territorial disputes. The size of the black ‘‘bib’’ on thebreast of male sparrows is a signal of how strong and therefore how dominantthat male is. Disputes can be settled easily with a quick check of the opponent’sbib size, meaning an argument can be resolved without the need for the riskybusiness of fighting. Recently, a further function of feather color has been dis-covered. The feathers of young chicks reflect not only visible light, but ultravio-let (UV) light as well. Some species such as great-tits can see UV light, andbrooding females use this ability to check on the health of their offspring. UV-reflecting feathers require a lot of energy to grow. A healthy UV glow tells themother that the chick is fit and well. By judging their chicks’ state of health fromtheir glow, parents can adjust the food they give to certain individuals.


The photonic crystal structures of peacock feathers are inspiring nano-technologists to produce sophisticated, man-made equivalents for use inoptical communications. By copying the melanin and keratin rod structure inpeacocks and embedding them on sheets of zinc, nano-technologists haveproduced tiny structures that can vary the color and intensity of light givenoff. These new biological optics have the benefit of not only producing a rangeof colors important for communications, but also they are much easier andenergy-efficient to produce because they use a production method that hasalready evolved in nature.

SKIN

Covering the entire body and with a surface area of some 22 square feet(2 m2), skin is our largest organ. Its thickness varies, from only 0.02 inches(0.5 mm) on our eyelids, to 0.15 inches (4 mm) or more on the palms of ourhands and soles of our feet. Remarkably, it accounts, on average, for about16 percent of our body weight. Although this may sound heavy and bulky, skinis really a thin, lightweight material. Human engineers have so far failed tomake a comparable material that is so thin, yet strong, flexible, waterproof,

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and stain-proof. Thanks to its impres-sive properties, skin plays a critical rolein our survival and has evolved over timeto be a highly specialized adaptation.

Skin is made up of two main layers—the outer epidermis and the inner der-mis. The deepest layer of the epidermisis constantly producing more cells.These new cells are gradually pushedtoward the surface of the epidermis bythose growing behind it. It takes one totwo weeks for a new cell to be pushedup to the skin surface. Eventually, asthey get to the outer layer, the cells willbecome filled with keratin, an extremelytough protein, and die. Keratinized cellsare gradually sloughed off with dailywear and tear, which is why they needto be constantly replaced.

There are two types of keratin foundin the body. Hard keratin is found inhair and nails (and horn and hooves inother animals). Soft keratin has a slightly

different molecular structure and is much more flexible, which makes it theideal material for skin. Thanks to soft keratin, skin is tough and waterproofand protects deeper cells from physical damage, infection, and desiccation.

The inner dermis is made up of strong collagen and elastic fibers, againcombining strength with flexibility. It is collagen that gives skin its firmnessand ‘‘plumpness.’’ With age, our skin loses collagen, which is why our skinwrinkles and sags as we get older. Within this tough core there are severaltypes of cells, each of which carries out a unique but crucial role. Blood vesselspuncture the dermis to bring nutrients to the growing cells of the epidermis.Perhaps more importantly, though, they play a key role in regulating our bodytemperature. When we are too hot and need to lose heat, our dermal bloodvessels dilate and fill with blood, allowing the heat it holds to dissipate intothe air. When we are cold, these blood vessels constrict so our blood, and theheat within it, remains in the core of our bodies and away from our extremities.This is why humans, especially Caucasians, look pale or even blue when we arevery cold—there is little blood flowing to our skin to give its usual color.

The dermis also contains sensory nerve cells to detect pressure and tempera-ture. It is thanks to these nerve cells that we can control our grip (feedback frompressure nerve cells tell us when we are gripping too hard or too gently) and thatwe can avoid potentially dangerous environments. Touching very hot or coldsurfaces triggers the nerves and elicits a lightening quick reflex in our muscles


A section of human skin showing the layers oftissue. [Gary Carlson / Photo Researchers, Inc.]

to pull ourselves away from harm. The dermis layer also contains follicle cellsthat produce hairs. Follicles are typically associated with oil and sweat glands,which keep hair and skin supple and waterproof. It is the sweat glands, though,that are perhaps the most significant feature of human skin. Sweating is anotherway in which humans keep cool. There are around 2.6 million sweat glands overan average human body, so they can quickly coat the skin in a film of water whenthe body gets too hot. This water is heated by the heat energy in our bodies, andas it evaporates heat is lost to the air. Being largely without body hair, humanscan shed heat much more quickly than other animals such as dogs, which havefur and very few sweat glands at all. This simple trait of having many thousandsof sweat glands over our bodies has been a key feature in shaping our entireevolution.

Being able to lose heat quickly is an important trait for those animals living inthe savannahs of Africa, and this includes our human ancestors. Overheating candamage the cells of the body, which is why many savannah animals are fairlyinactive during the day. Early humans may have been different, though. Theymay have been able to brave the soaring temperatures thanks to their ability tosweat and keep cool. This would have allowed them to adopt a particular wayof life.

Early humans were most likely scavengers rather than hunters. Not beingparticularly quick, chasing down living prey would have been difficult, notto mention dangerous. But with keen eyes, humans could have spotted cir-cling vultures and made their way quickly to the carcass below. Running overlong distances without overheating would have allowed humans to be success-ful scavengers—especially at times when other animals would have beeninactive.

Further on in the history of human evolution, this ability to run long distan-ces would have been used, as it is today in some hunter-gatherer societies, tochase down prey until it collapsed from heat exhaustion. This method,although grueling, incapacitates the prey without the danger of having totackle it directly. The peoples who still employ this hunting technique willonly perform the behavior when temperatures are over 100°F, when they knowthat animals such as antelope will suffer in the heat. Humans could only haveevolved this behavior thanks to their skin and the specialized sweat glands,which make the difference between keeping cool and suffering heat stroke dur-ing such vigorous activity in the high temperatures of the day.


Skin plays such an important role in protecting the body that we simply can-not live without it. Burns victims with more than 50 percent damage to theirskin used to have little chance of survival. Recently, artificial skins have beendeveloped and successfully used to graft on to burn victims. An artificial dermiscan be made from cow collagen and a carbohydrate from shark cartilage.

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This is then covered with a thin silicon wrap, which mimics the tough epider-mal layer. When used in surgery, this artificial skin is not rejected by thepatient’s body but instead acts as a temporary scaffold to encourage new skinto grow. This artificial skin is not a permanent solution, but it offers criticalprotection while the body recovers and new skin is grown or skin graftstake hold.

BIO-CERAMICS

There are many shelled crea-tures that walk and crawl theearth. Many of these species arethe soft-bodied, unsegmentedinvertebrates called the mollusks.These animals are found in marinewaters, fresh water, and on land.They include snails, slugs, limpets,mussels, oysters, squids, and octo-puses and are one of the most suc-cessful groups of animals that liveon this planet. Their body is madeup of a muscular foot for movingabout and a main body (the dorsalhump) covered by a piece of skincalled the mantle. It is this mantle

that is the organ that secretes the shell that so characterizes so many of theseanimals. The materials used to build this shell are a form of calcium-basedminerals that are very much like the ceramics made by humans. Not onlyare these materials used for shells, but they are also found in mollusks’ teeth,which are perhaps the hardest that have evolved in any animal.

Anyone who has walked along a beach and stopped to pick up a seashellwill know that mollusks who live in the ocean make beautiful shells. Mollusksget the materials they need to build these shells by extracting various calciumcarbonates from the water in which they live. Typically, these calcium miner-als are absorbed in the forms known as calcite and aragonite. The molluskconstructs these minerals into layers of crystals embedded in proteins andother organic compounds, which are then secreted to make the hard shellthat protects their soft and vulnerable body. The mineral crystals arearranged as microscopic ‘‘bricks’’ that can be bound together by a mortarof proteins and sugars. Closer inspection reveals that these mineral bricksare stacked on top of each other with proteins to create a layered effect,which is strong, flexible, and light. The net result of this natural engineeringis a material that is up to 30 times stronger than calcium carbonate made inthe laboratory.


A scanning electron micrograph of a snail radula.The radula is the tongue-like organ found in allmollusks. It is studded with rows of mineral-encrusted teeth. [Clouds Hill Imaging Ltd. / PhotoResearchers, Inc.]

Mollusk shells are incredibly versatile materials, thanks to their innatestrength and the way that they are layered, which affords movement and flexi-bility. They can withstand the enormous pressures of the deep ocean and theincessant pounding of waves, and they are strong enough to cope with theattacks of predators. Despite this strength, mollusk shell is very lightweight,allowing its inhabitant the freedom to move about. The flexibility of thematerial also allows the animal inside to grow.

The calcium mineral shells of mollusks are well-known successful adapta-tions that have allowed sufficient protection to conquer both land and sea.What is perhaps less well-known, though, is that a similar ceramic materialis also found in the teeth of mollusks to give them extraordinary hardness.The teeth of mollusks are embedded on a mobile organ called the radula,a tongue-like organ that is used to rasp at rocks to scrape off the algae thatgrow there. To remove their food successfully, mollusks have evolved aradula that is covered with up to 150 rows of tiny, but extremely hard, teeth.These teeth are so hard that some mollusks have even evolved to predateother mollusks, using their teeth to drill through the hard shells to get atthe soft bodies within.

The radula continues to grow through the mollusk’s life as the tip is wornaway from its constant activity. Softer teeth at the back of the radula graduallyharden as they get closer to the tip of the tongue. As the teeth mature, they arebuilt up with many layers of minerals. The core of the tooth is made up ofiron-containing minerals such as limonite and lepidocrocite as well as the cal-cium mineral hydroxyapatite, which makes up some 70 percent of bone inmammals. This core is known as an organic scaffold around which the hardouter shell of the tooth can be built. This hard outer layer is made up of amaterial with much more tightly packed iron and silicon minerals than thecore, giving the tooth a strength that can withstand the scraping across toughrock. As the teeth mature, more minerals are added, giving them strength. Ithas been shown that this maturation is a carefully controlled process so thatthe minerals are added to the teeth in precise amounts and at exactly the righttime. The whole process provides mollusks with a tough set of teeth that canget food from some of the most unlikely and inaccessible of places.


The strong, flexible mollusk shells are being used as a model for developingflexible concrete, which can be used in structures that must endure extrememovement, particularly tall buildings found in places susceptible to earth-quakes. They have also been used as a model for new ceramics, includingcoatings for turbine blades in jet engines that need to withstand extreme stress,heat, and corrosion. The ceramics industry is equally interested in themollusk’s radula teeth, the structure of which is being copied to be applied tothe fields of dredging, drilling, and mineral processing.

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MUCUS

Mucus will be familiar to us all—wetend to produce a lot of it when we areinfected by the common cold virus. Butwhat exactly is this slimy substance?It is common and is produced by verte-brates, invertebrates, bacteria, and fungialike. Despite having many functions innature, the structure is essentially thesame. It is made up principally ofmucins, which are one form of a specialgroup of proteins called the glycosylated

proteins (a protein molecule with a carbohydrate [sugar] molecule attached toit). Other proteins are mixed in with mucins, and this basic mix of moleculesgives mucus its property of a sticky, viscous fluid.

In humans and other mammals, mucus contains molecules that are part ofthe immune system. It lines the lungs and airways, the intestines, the genitals,eyes, and auditory systems, offering lubrication and protection from infection.It plays a similar role in other animals, although there are certain animals thathave evolved unique uses of this essential material.

The hagfish are thin, primitive, worm-like creatures, closely related tolampreys, found mainly in the Pacific Ocean, some 4,000 feet below the sur-face. They belong to the class of organisms called theMyxini, which appropri-ately enough means ‘‘mucus.’’ This is especially apt because the hagfish hasevolved an entire life based around the slimy material. Hagfish mucus, though,is unlike the stuff produced by other animals. Mixed in with the basic structureof mucins is a unique kind of fibrous protein that is very similar in structure tocollagen. These fibers are very long, around which mucins cluster and producea very cloying, sticky mucus. This sticky mucus swells when it comes into con-tact with seawater, a property which is exploited by the hagfish when it hunts.

Having a very slow metabolism, the hagfish can remain motionless on theocean floor for months. When an unsuspecting fish passes by, though, it isroused from its torpor and will swim toward its prey. Rather than stopping asit gets to its quarry, the hagfish will swim inside the fish through its mouth orgills. Once there, it will quickly secrete its mucus, which soon overcomes thefish’s gills, suffocating it. Even large fish species have no defense against thisunique attack. Once its prey has been killed, the hagfish will then eat it fromthe inside out, using the body as a temporary shelter.

To suffocate its prey, the hagfish has to produce a lot of mucus. But its trickis that 99.996 percent of the mucus it produces is made from seawater. Only avery tiny amount is made from its fibrous protein and mucins, but thanks totheir unique molecular structure the mucus still remains sticky and so can suf-focate the prey. Despite investing in only small amounts of its own buildingmaterial, the hagfish can produce as much mucus as it needs. This is the most


The pacific hagfish, Eptatretus stoutii. [TomMcHugh / Photo Researchers, Inc.]

dilute mucus produced by any organism, and it is certainly the most efficient. Itis a highly specialized adaptation that allows the hagfish to lead a way of lifethat no other organism is capable of.

This immobilizing mucus is also used by the hagfish as a defense, creatingfor itself a protective cocoon when under attack. This deters predators, buthow does the hagfish itself extract itself from its sticky predicament? Its solu-tion is a remarkable one. Hagfish are the only animal able to tie themselvesin a full, overhand knot. This knot starts at the head and works its way backover the body, scraping the sticky mucus away as it goes. With a flash of gym-nastic contortion, the hagfish is free and can go about its business once more.

Also to be found in the sea is the fat innkeeper (Urechis caupo), which is a typeof spoon worm that lives in the mud flats of the Pacific coast. It is a fairly indis-tinctive creature some 6–8 inches (15–20 cm) long. It lives within the muditself, making for itself a U-shaped burrow, about 3 feet (1 m) long, in whichit sits. The burrow provides excellent protection from predators but doespresent a problem for getting food—to leave would expose it to the foragingbirds that patrol the coastal flats looking for food. To get around this problemit feeds from within its burrow. To do so, it exudes a cone of mucus, about4 inches (10 cm) long, which fills part of the burrow. As the mucus is produced,the forward part of its body is positioned inside the net. This is then foldedback to position the net and to keep it taut and in the correct shape.

The structure of this mucus net is such that water can pass through, but tinyfood particles cannot. To maximize its catch, the innkeeper worm undulates itsbody to pump water through its burrow, creating a current flowing though itsmucus sieve. The innkeeper worm can pump up to 23,000 liters of seawaterthough its burrow each day. To get the maximum amount of water flowingthrough the net, the innkeeper worm contracts its body to about one-quarterof its normal diameter, allowing water to flow past it and into the net. Afterabout 20 minutes of pumping water through its burrow, the innkeeper wormfeeds off the particles of food collected. It does this by detaching the net andfeeding it, along with the food trapped there, into its mouth using its longproboscis. It can do this very quickly, finishing its meal in under a minute.Thanks to its unique use of mucus, the innkeeper worm can feed almostconstantly without expending much energy or risking predation.

Away from the ocean, there is another animal that has made full use of this ver-satile material. Dogs have an amazing ability to sniff out faint smells and to distin-guish one from another. It is this trait that makes them such good hunters andsuch effective companions for narcotics police officers. A dog’s nose has manymore chemical sensors than a human nose, but it seems that a great deal of its sen-sitivity owes much to the mucus which lines it. The inside of the nose is coveredwith very thin tubes filled with mucus. Thanks to the mucus, these tubes effec-tively ‘‘pre-sort’’ smells before they get to the more refined sensors, which dothe detailed work. As chemicals are absorbed through themucus at different ratesthey arrive at the sensors below at different times, albeit a fraction of a second.

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This means that the chemicals making up a smell can be broken down and ana-lyzed by the nasal sensors in great detail. A dog’s tremendous sense of smell hasallowed it to hunt efficiently and evolve a complicated array of behaviors to en-able living in social groups—all possible thanks to mucus.


The hagfish’s mucus is coming under very close scrutiny in the field ofemergency medicine, particularly military emergency medicine. Although ithas yet to be replicated it would be extremely valuable as a ‘‘space-fillinggel,’’ a viscous fluid that can fill large wounds and help stop bleeding. Mucusin nature also typically carries antibacterial molecules that would help treatinfected wounds.

Recognizing the important role mucus plays in a dog’s sophisticated organof smell, engineers are applying a layer of slime to odor-sensing ‘‘electronicnoses.’’ These devices are used for a range of purposes, including to detectspoiling food. To date, electronic noses have not been great at distinguishingodors, and they tend to be specialized in detecting one type of smell. By apply-ing a layer of artificial mucus over the sensors, however, they are able to distin-guish certain odors by detecting the time it takes for the component chemicalsto diffuse through the layer of slime.

NATURAL GLUES

Glues and adhesives are extremely useful materials that have been key to manyhuman engineering endeavors. Adhesives have been used on spacecraft, in ourhomes, in our cars, in businesses, in huge skyscrapers, and even in art and craftsclasses in kindergarten. We have developed glues that can stick nearly any twosubstances together. But man-made glues are not the most versatile of substan-ces. They can take a long time to set, and they are often difficult to apply withoutalso bonding with the applicator (or indeed our fingers). Glues in nature, on theother hand, have a much wider range of uses and properties. Invariably, theiradhesiveness is finely tuned to whatever purpose they are required for and theycan be delivered and applied quickly and without fuss (or mess).

Spiders are truly a living factory of amazing natural materials. Silk is wellknown to be a versatile, strong, and sticky substance that spiders have used forvery many behaviors. Some spiders, though, also produce a variant on silk thatis much more like a fast-setting glue. Spitting spiders (of the family Scytodidae)are aptly named. In the blink of an eye, they can fire a sticky fluid from theirfangs and trap any unwitting prey within range. Using its mouthparts (its chelic-erae), the spitting spider can direct the sticky spray backward and forward in azigzag pattern to cover as large an area as possible. The glue is squirted by aquick contraction of the fang muscles, and after only 0.14 seconds the prey isentangled and unable to escape.


The glue also contains paralyzingvenom that further subdues the prey,allowing the spider to approach anddeliver the final killing blow with itsfangs. The speed of this is critical asmany of the prey species hunted by spit-ting spiders are fast moving, such asmosquitoes or jumping spiders. What isremarkable is that this adhesive is so per-fectly adapted to its use. It can be storedas a liquid in the spider’s body and yetmidair become sticky enough to ensnarea tasty morsel. This is a direct functionof the molecular properties of the glue,which has yet to be fully replicated inman-made glues.

Spitting spiders are not the onlyanimal to use glue as a weapon. Thecurious-looking velvet worms (Onycho-phora), which look like caterpillars with-stumpy legs, are furnished with a pair ofdeadly slime glands on either side oftheir mouth. When hunting, the velvetworm will rear up on its legs and spit atits prey just like the spitting spider.Again, this is a fast-moving and rapidly-setting jet that can trap prey (such asants) before they can escape. And they have a good range at about two feet(0.6 m). What is remarkable about the velvet worm, though, is how it copeswith potentially messy moments when its glue falls on its own body. Unlikehumans stuck together with super glue who may take several painful momentsto free themselves, the velvet worm has a handy trick that comes to the rescue.Its body is coated with a fast-acting solvent that instantly frees any body partsthat may have become stuck by this tremendous adhesive, allowing it to useits deadly glue without any embarrassing moments of self adhesion.

One of the most difficult places humans have found to use adhesives isunderwater. Yet there are species who do produce an underwater glue,and for a very good reason. Animals like mussels and barnacles live and feedby sticking themselves to rocks, boats, ropes, and even large sea-bound mam-mals like whales. The glues they use must be very powerful, as they needto work on wet, salty surfaces and against the relentless pounding of thewaves.

Before settling on a spot, all shellfish larvae are free-floating organisms thatdrift on the currents of the ocean. To develop into adults, certain species of

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The water-resistant glue-like protein threadsthat attach mussels and other bivalves torocks. [James King-Holmes / PhotoResearchers, Inc.]

shellfish larvae seek out a specific spot on which to settle. They will smell outplaces where marine bacteria have attached themselves and are living. Thesemarine bacteria produce a glue to stick themselves to a surface, and the indus-trious larvae make use of this glue to stick themselves on, too. Over time, andas the larvae develop into adults, they make their own glue with which to stickthemselves on. Mussel larvae are able to produce a glue that can stick to allsorts of surfaces: rock, wood, metal, teeth, bone, and even teflon, a substancethat was designed to resist any adhesive.

Man-made glues produce a very poor bond when mixed underwater, so howdoes the mussel do it? The mussel’s glue gland comprises two separatecompartments. One produces resin-like proteins, and the second produceschemicals that behave like hardeners. On entering the water, the proteins andchemical hardeners mix and, in minutes, solidify into a near unbreakable bond.This seems fairly straightforward, but it turns out that the mussel producesaround 10 different proteins that tangle up with each other to produce thehardened glue. This complexity is very difficult to recreate, which is why a verystrong, man-made underwater glue is still some way off, although huge leapsforward have been made thanks to the insides provided by the humble mussel.For the mussel, though, evolution has provided it with an adaptation thatallows it to live in one of the most physically violent places on earth withoutbeing swept away to sea.


The underwater glues of shellfish are perhaps the most interesting forhuman engineers. Adhesives that work well in seawater can be used to makerepairs to the hulls of ships and to the stations of piers and oil rigs. There havealso been suggestions of using these glues to repair damaged body organs thathave moist surfaces that are not easily stuck together—or even to stick softtissue to harder tissue like muscle to ligaments or ligaments to bone. Dentistsare watching this glue research carefully, too. Reconstructive dental surgeryneeds a glue that can be applied while still soft, bonds quickly in a wet environ-ment, and adheres strongly to teeth and bones. Adhesives currently used arenot great at bonding these kinds of surfaces, especially when wet. Mussel glues,on the other hand, can do exactly that.

GECKO FEET

The lizards that make up the gecko family (Gekkonidae) are in a class of theirown when it comes to their ability to stick to seemingly unscalable surfaces.Found in forests, they have no problem clambering over trunks and branchesin any direction. They can cling upside down and even on sheer surfaces suchas glass. There is no doubt that this ability must come from the adhesive proper-ties of its feet, but until recently it has not been clear how that is achieved. Close


inspection reveals that it is notdown to a secretion of somesticky fluid. Nor is it true thatgeckos’ feet are covered in tinysuction cups, as was previouslythought. What has evolved ingeckos is a much more ingen-ious solution.

A close look at a gecko’s feetunder a high-powered micro-scope reveals that it is coveredin a dense network of millionsof tiny hairs made from kera-tin. These hairs, called setae,are very tiny indeed. Oneseta is only as long as thediameter of a human hair,about 100 millionths of a meter (100 micrometers). They are only 5 millionthsof a meter (5 micrometers) wide. So tiny are these setae that there can be up toabout 2 million on each gecko foot. And it doesn’t end there. The tips ofeach of these tiny setae branch out into even finer hairs called spatulae. Thereare about 1,000 of these spoon-shaped spatulae on each seta. As you mightexpect, the spatulae are very small indeed. They are only about 200 nanometers(200 billionths of a meter) wide—less than the wavelength of visible light.

So how do these millions of tiny setae and spatulae allow geckos to runupside down on the ceiling? At the molecular level there are certain forces thatbind various surfaces together. Probably the best known of these molecularforces is the hydrogen bond, a weak attraction between hydrogen atoms. It isthis bond that causes water to cling to surfaces and get drawn up thin capillarytubes. But it is another, even weaker molecular bond that the gecko makes useof. It is called the van der Waals force, which is a very weak attraction thatoccurs between any two surfaces no matter what they are made of. Eachspatula exerts this weak van der Waals force and will create a weak attractionto any surface it comes into contact with. On its own, this would not create aparticularly strong bond, but considering there are many millions of thesespatulae that will be in contact with a surface at any one time, all together theycreate a very strong bond indeed.

The collective force exerted by the spatulae mean that a gecko could supportall its weight, hanging upside down, with just one toe. The spatulae of 1 millionsetae could support a 45-pound (20-kg) child. This is more than enough forceto keep a 0.2-pound (100-gram) gecko stuck to the ceiling. The question is,then, how geckos can move their feet at all with such strong forces holdingthem to a surface. The answer lies in the angle at which the setae and spatulaelay across a surface. When the foot is put down, the setae lay flat. They will

MATERIALS 101

A scanning electron micrograph of the underside of agecko foot showing the tiny rows of hair-like setae.[Andrew Syred / Photo Researchers, Inc.]

cease to exert their force when theyare angled away from the surface,though. All the gecko has to do isroll its toes upward and its foot willbecome unstuck. The strong forcesexerted are clearly no hindrance tothe gecko, as they can move atfairly high speeds, faster than onemeter per second even up smooth,vertical surfaces.

It is the direct contact of spatu-lae with a surface that allows agecko to cling on without slipping.Any dirt on the feet would there-fore reduce their adhesiveness.It is strange, then, that geckos nei-ther groom their feet nor secreteany cleaning fluid that might wash

dirt away. Yet gecko feet do not lose their adhesion over time. It seems thatthe setae and spatulae are self-cleaning. As they walk, any dirt is transferredfrom their feet to the surface they are walking on rather than sticking to theirfeet. This seems remarkable given the attractive forces that gecko setae seem,collectively, to impart. Why does the dirt not stick to the setae? Again, theanswer lies in the molecular forces imparted by the setae. All materials impartweak, attractive van der Waals forces, but it seems that gecko setae are madeof a material that have a weaker force than usual. Overall, this does notmatter because the setae work together to produce an overall very strongattraction. What it does mean is that a tiny speck of dirt will be moreattracted to the surface over which the gecko is walking rather than to its feet.The activity of walking causes dirt to stick to the surface on which the geckois scurrying over. After only a few steps, dirty feet are cleaned and the gecko’sfeet are once more fully adhesive.

We might marvel at the gravity-defying abilities of a gecko, but what are thebenefits of such a skill? Lizards provide a tasty snack to many predators, and inthe tangled and stony forests where the gecko lives, making a sure-footed andquick escape is the difference between life and death. When the gecko itself ishunting, the ability to scale improbable surfaces allows it to get to resting insectsthat otherwise would be well out of reach. The adhesive properties of a gecko’sfoot is not simply an amazing party trick but a key adaptation for survival.


The problem with wet adhesives like glue is that they tend to be single use.If they can be detached and reapplied, they rapidly lose their adhesiveness asthey get clogged with dirt. To recreate a dry adhesive like gecko setae would


A higher magnification scanning electron micro-graph of the underside of the gecko foot showingthe microscopic spatulae, which allow the gecko tocling to nearly any surface. [Andrew Syred / PhotoResearchers, Inc.]

be extremely useful where surfaces need to be joined, unjoined, and rejoined anumber of times. Velcro strips are a crude option, but that relies on attachinga specialized strip to each surface. The attraction of a setae-like adhesive is thatit can stick to anything (with the exception of Teflon, which was designed spe-cifically to prevent even van der Waals adhesion) without having to treat thesurface.

Thanks to the simple principle behind gecko feet, synthetic setae are nowbeing designed. So far, engineers have fabricated arrays of plastic pillars, simi-lar to setae, that are little more than two millionths of a meter (2 micrometers)tall, spaced about the same distance apart. So far, only a very small square ofthis material can be produced because of the difficulties involved with the fab-rication process. However, this sample is proving to be very successful.A 0.08 square inch (0.5 cm-square) piece of tape is sufficient to hold an objectover 0.2 pounds (100 grams), just as adhesive as a gecko’s foot.

There are many potential applications for ‘‘gecko tape.’’ It can be used in avacuum, so it may have applications in space. It can be used in microsurgeryand in handling silicon wafers. Some engineers are trying to use the technologyto design tiny robots capable of climbing over walls and ceilings just like livegeckos. These gecko-bots can be used to look for survivors in burning and col-lapsed buildings or could even be used to explore the tricky terrain of Mars.This simple but hugely effective adaptation truly has a tremendous range ofapplications if it can be replicated on a large scale.

RESILIN

For many years, the jump of a flea was regarded as a major zoologicalproblem. This tiny insect of only a few millimeters is capable of jumpingover 20 times its own body length. What’s more, it seemingly never getstired. Should they be so inclined, fleas can jump 600 times an hour for threedays without needing to eat any food. The reason why they need to jump sohigh and so frequently is clear. When they do eat, adult fleas eat only blood,which means climbing onto an animal to feed. One of the adaptations for thislife of clambering over other animals is to have no wings, which makes itmuch easier to push through the thick hair of its host. With no wings,though, the insect needs to rely on its tremendous jump to reach its foodsupply. This is why the flea needs to jump such great distances, but how doesit do it?

Fleas have been called insects that fly with their legs. This is because, overthe thousands of years of natural selection, they have evolved smaller andsmaller wings until only a very tiny remnant has remained. This makes it easierto navigate the tangled fur of its host, but it has another important role. It isthe vestigial remains of their wings that are involved in setting themselves upfor their almighty leap. More precisely, it is one part of the tiny wing remnantthat is important. The pleural arch is the hinge that, in the flea’s ancestors,

MATERIALS 103

used to connect the wing to the thorax(chest) and the muscles beneath. It is thistiny structure that is the secret of a flea’sprodigious jumping ability.

The flea’s pleural arch is horseshoeshaped and can be flexed when compressed.Beneath it, though, is a small pad made froma unique protein called resilin, a highly elas-tic protein very similar to dense rubber.Like all elastic materials, resilin absorbsenergy when it is compressed and releasesit again when it springs back into its originalshape. Unlike man-made rubber that trans-fers little energy when it bounces back intoshape, resilin is highly efficient. It releases97 percent of the energy stored inside itduring compression.

Resilin is undoubtedly a superb material for the flea to have at its disposal. Buthow does it make the best use of it? When readying itself for a jump a flea willbend and bunch up its hind legs much like we would if preparing to leap froma standing start. This causes the pleural arch to bend and the resilin beneath tocompress, storing energy.Where the hind legs meet the body, fleas have a simplelocking mechanism that allows them to hold the compressed pleural arch andresilin pad in place without needing to keep the muscles of the leg tensed. It alsoprevents an unwanted release that could see the flea missing its intended targetcompletely. When it is ready to jump the flea can release the catch, causing theresilin pad and pleural arch to spring back into shape, forcing its legs straight.This sudden release of energy propels the flea high into the air and hopefullyonto an unsuspecting animal where the flea can settle in and feed.

There is a tremendous amount of energy that can be stored and released inresilin. A flea’s jump reaches an acceleration imparting 140G of force in littlemore than a millisecond. Muscles would never be able to simulate this feat.They contract too slowly and would rapidly become fatigued. In fleas, theresilin pad simply springs back into shape and it is immediately ready foranother leap. It even works just as well at low temperatures, which otherwisereduce the efficiency of muscle.

Resilin is such a versatile material that it has evolved to be used in many spe-cies of insect. The durability and elasticity of resilin is used in flying insects inthe hinges of their wings. Thanks to resilin, bees can flap their wings in almostfrictionless motion 500 million times throughout their life. This durability ofresilin is important because insects do not continue to produce it as adults, soit is not replaced and repaired.

The structure of this remarkable protein is quite simple. It is made up of anumber of short chains of amino-acids, the building blocks of proteins.


When jumping, a flea’s hind legs extendrapidly thanks to the elastic resilin padfound at the base of the leg. This can becompressed and then released by the fleato power its jump. [Steve Gschmeissner /Photo Researchers, Inc.]

One key amino-acid in these chains is proline. Proline has a unique, elbow-shaped structure that it causes the protein chain to bend into a U-shape. It isbelieved that a succession of these U-bends creates a spiral that can compressand stretch exactly like a spring. These protein springs can be repeated overand over to produce as much elastic resilin as is needed.


Until recently, the best elastic material scientists could produce was asynthetic rubber called polybutadiene. This rubber was way short of resilin inefficiency, releasing only 80 percent of energy absorbed after compression. Butwith such an amazing material available in nature it is little wonder that scientiststried to better their efforts by replicating resilin. Scientists can now successfullyisolate the resilin gene (from a fly), insert it into a bacterium, and harvest theprotein produced. This harvested resilin seems to show the same elastic anddurability properties as that found in nature. Now, the task is to fully test itand apply thematerial to a range of uses. Engineers are exploring its use in spinaldisk implants, microelectronic mechanical devices, drug delivery vehicles andsystems, and as synthetic prosthetic veins and arteries.

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5

BUILDING STRUCTURES

BUILDING STRUCTURES—HUMAN INVENTION

If humans were instantly wiped from the face of the earth one of the mostindelible marks we would leave is the multitude of large structures we havebuilt. These remarkable feats of human engineering cover the earth, from themonuments of the ancient world through to the skyscrapers and huge edificesof our modern cities, and even the immense dams able to hold back and har-ness the power of the planet’s great rivers.

For the vast majority of the 100,000 years or so of human existence, build-ings were fairly insignificant and huts were the peak of our architectural abil-ities. However, around 5,000 years ago in the Fertile Crescent, the arc ofland watered by three enormous rivers—the Nile, Euphrates, and Tigris—allthis changed as our ancestors turned from a hunter-gatherer existence tosettled societies underpinned by agriculture.

At this time, humans began to build more elaborate buildings which grewinto the first human cities. Although these ancient societies lacked themachines we have today, they were capable of erecting some very impressivestructures that still have the ability to impress. Take the pyramids of Egypt,which are huge monuments to the dead. They are colossal tombs that werebuilt as symbols of the power and wealth of the dead kings they were builtto house. The great pyramid in Egypt was the tallest man-made structure onearth for 3,800 years following its completion in around 2560 BC. In its dayit stood some 480 feet (146 m) high, but the loss of the casing stones and ero-sion leaves it at 453 feet (138 m) today. Approximately 600,000 stone blockswere needed to build the pyramid, and the whole structure weighs in theregion of 5.9 million tons. It was built over a 20 year period in such a precise

way that it would severely press the building techniques of the modern day ifwe tried to recreate it. The joins between the huge stone blocks are so perfectthat we still have no idea what techniques the builders used to cut and shapethem, but the finished, albeit ancient, structure clearly shows they weremasters of their art.

Apart from the Egyptian pyramids, the world is dotted with other, ancientstructures that still attract millions of tourists each year. However, the mostimpressive human structures have been built following the industrial revolu-tion, when advances in science and engineering made truly astonishingconstruction possible. Metallurgists were able to produce good quality ironand eventually steel that would form the internal scaffolds of the new age ofstructures. Stone is still used in buildings to this day, but it was replaced inthe really ground-breaking structures by concrete and bricks—cheap buildingmaterials that could be tailored to suit various needs.

With these new materials at their disposal, engineers continually pushed theboundaries of possibility, a trend that continues to this day. In the 1920s and1930s, engineers in New York and Chicago competed with each other to buildthe tallest buildings, and in doing so they produced such famous landmarks asthe Chrysler building and the Empire State building. With land prices soexcessively high in city centers the world over, the pressure to build upwardis as great as ever. The competition to build the tallest skyscraper has neverreally died, and a visit to any major city in the world will be dominated by viewsof towering buildings. Taipei 100 in Taiwan was the tallest complete sky-scraper, measuring 1,670 feet (509 m) to the top of its tallest spire. However,this was easily surpassed in 2009 when the Burj Dubai was finished. This enor-mous building reaches 2,684 feet (818 m) into the air, making it the tallestman-made structure on earth.

Skyscrapers aside, humans have also constructed other enormous struc-tures, and some of the biggest of these are dams. The Three Gorges Damover a stretch of the Yangtze River in China is due to be completed by2011 at a cost of $30 billion. When finished it will be the largest dam everconstructed. The scale of this building project is immense. The dam wall is7,575 feet (2309 m) long, 607 feet (185 m) high, 377 feet (115 m) thick atthe bottom, and 131_feet (40 m) wide at the top. The project has used960.5 million cubic feet (27.2 million m3) of concrete and 463,000 tons ofsteel, enough to build more than 60 Eiffel Towers.

Many of the earth’s great rivers have been tamed by dams. However, largebodies of water and the barriers they present provide other problems for engi-neers to solve. One of the most impressive of these solutions is the projectwhich gave the United Kingdom a fixed link to continental Europe—theChannel Tunnel. This feat of engineering enables trains to pass under theEnglish Channel at high speed for a distance of 31 miles (50 km). The projectinvolved tunneling through the seabed at an average depth of 160 feet (48 m)to produce two train tunnels and one service tunnel, two of which were lined


and fitted out with tracks and other equipment to allow trains to pass through.To make things even more complicated, the tunnel was completed by twoseparate teams, one working south from the United Kingdom and the otherworking north from France. Their efforts had to be precisely matched so theymet somewhere underneath the channel. Eleven huge tunneling machineswere used to make the tunnels and line them with curved, concrete slabs.The project took six years and depended on 15,000 workers.

Human ingenuity has enabled the construction of some truly remarkablestructures, but how do these compare to the structures we can see in nature?Nature’s structural ingenuity is very different from what humans haveproduced, but it is nonetheless impressive thanks to life’s ability to adapt toenvironment and circumstance. Evolution has come up with some incrediblyelegant solutions to a bewildering array of problems.

TERMITE TOWERS

Some of the most impressive structures in the natural world are those con-structed by insects, particularly those that live in complex societies. The mostwell-ordered insect societies are those formed by ants, bees, wasps, and ter-mites. In terms of sheer engineering achievements, it is the latter group ofinsects that stands out. The structures that they build in which to live not onlyoffer simple protection from the elements and predators but are carefullydesigned and engineered to allow them to live in style and comfort.

The termites are unrelated to the other social insects—their closest relativeis in fact the cockroach. A termite colony can contain hundreds of thousands ofindividuals, most of which are workers. These workers are not much to look at.They are small, practically blind, and soft-bodied, but it is these seeminglyunremarkable animals that are responsible for constructing some of the mostimpressive structures found in nature.

The worker termites do not build from detailed plans. There are no archi-tects and no foremen to manage the endeavors of these tiny insects, yet theseunseeing builders are indeed following instructions. Their actions in their nestare influenced ultimately by the egg-laden queen who lives in a specialchamber at the center of the mound. Chemicals produced by the queen act likemessengers to give each and every termite a certain amount of guidance in itsactions.

Using these simple cues and the innate abilities they are born with, theworker termites construct nests of incredible size and complexity, and it is onlyin recent years that we have started to realize how incredible these structuresare. Often, these nests are disparagingly referred to as mounds, implying a sim-ple heap of material without any internal structure. In reality, nothing could befurther from the truth. Any termite nest, particularly the large structures con-structed by some of the Macrotermes species, is a masterpiece of organic archi-tectural design. In terms of dimensions, some African species make towering

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A termite mound. [Georg Gerster / Photo Researchers, Inc.]

structures up to 30 feet (9 m) high containing a labyrinth of passages andchambers. If we scale these structures up according to the relative heights ofthe builders, they would dwarf the tallest human-built skyscrapers. The work-ers of the species responsible for these insect towers are a mere 0.2 inches(5 mm) long, so the tallest mounds are equivalent to humans building askyscraper more than 1.2 miles (2 km) high.

Depending on the species in question, termites use combinations of soil,saliva, and their own excrement to produce a paste that dries in the equatorialsun to a substance with properties similar to very hard brick mortar. All ter-mites protect their nests vigorously, and when the nest is breached, which itinevitably is by predators, the worker termites are quick to repair the damage,and in a few hours huge holes in the nest can be seamlessly repaired. Foragingtermites will even build tunnels out of the same material for them to travelthrough. Being so soft-bodied, they are extremely susceptible to the elements.A mortar tunnel allows them to move about in a controlled environment,protected from predators and the sun.

Size and building materials aside, what sets termite nests apart is their inter-nal complexity. There is a very good reason for this complexity. Termitemounds are often situated in the middle of a baking desert, with no shade tooffer protection from the relentless sun. Temperatures can easily soar topotentially lethal levels, not only for the termites themselves, but for thefungus (Termitomyces) that they farm for food at the heart of their homes.To ensure the fungus can grow at optimal temperatures, the whole moundstructure is designed to operate as a sophisticated air-conditioning unit.

A cross section through the structure reveals a central passage in the tower,reminiscent of a chimney. Branching away from this main chimney is a com-plex series of passages akin to the veins in an arm. The nest, where thetermites live, itself is a spherical structure in the ground below the tower.The whole elaborate edifice above the nest is part of a remarkably elegantclimate-control system. To ensure the nest stays healthy the structure as awhole ‘‘breathes,’’ powered by the ebb and flow of the wind. The obviouspart of the termite mound, the tower, extends into the air where winds areslightly stronger. The wind blowing across the top of the tower pushes andpulls air in and out of the subterranean nest chambers. If the colony growsand the air in the nest gets a little stuffy the workers extend the height ofthe tower, increasing the rate at which the air is exchanged.

Air is drawn up through the mound thanks to the tall chimney, but a keypart of the unit is the chambers that are dug deep into the soil. The termitesdig deep enough to get to the cool, moist soils that are not heated by the sun.As the air is drawn up through the mound, the cool deep-soil air is suckedthrough the mound, cooling the whole colony. The result of this simple, buteffective design is that the mound is kept at a constant 87°F, the perfect tem-perature to grow a crop of fungus. What is remarkable is that this temperatureis achieved even when the surrounding environment fluctuates from 34°F at


night to over 100°F at noon. This is a reliable system that comes at nocost, which consistently outperforms many of today’s air-conditioningsystems.


Recently, scientists have been trying to unlock the secrets of how these ter-mite structures are made, in the hope of developing buildings for humans thatwill not require expensive and inefficient systems for heating and ventilation.However, such technology has already been used by humans since the fourthmillennium BC. Persian wind-towers (also known as Badgirs) use complicatedarrangements of vents and tunnels to cool buildings from the wind alone.In fact, so successful is this technology that ice can be produced in ice wellseven in the hot climate of the Middle East. More widespread use of this tech-nology—potentially honed by what we can learn from termites—could resultin free (or at least cheap) air conditioning, which would be both a cost savingand an important contribution to cutting our energy output in the quest tofight climate change.

TREES

Plants first appeared on earth some 465 million years ago. Even this long ago,these primitive organisms showed many of the characteristics of modern plants.They had a waxy outer cuticle to preserve water, a vascular system for transport-ing water and nutrients from roots to leaves, and small openings in their leaves

(stomata) to draw in carbon dioxidefrom the atmosphere and to expeloxygen. Eventually, this plant res-piration would radically changethe makeup of the atmosphere,allowing the evolution of oxygen-breathing life forms, such ashumans.

The early plants of the Ordovi-cian period would not have beenvery tall, however. Mostly, theywould have reached only a fewinches. There are tree-like organ-isms that have been found in thefossil record from this time, but itnow has been shown that thesewere not trees at all, but giantfungi that would have fed off bac-teria, algae, and lichens that would


A cross section of a branch from a hardwood tree.The concentric rings show successive periods ofgrowth. The holes show the tube-like xylem andphloem cells that strengthen the tree and carry waterand nutrients from the roots to the leaves. [CloudsHill Imaging Ltd. / Photo Researchers, Inc.]

have formed a crust over the soil. These fungi are called Prototaxites and grewup to 20 feet (6 m) high and 3 feet (1 m) wide.

These early plants would not have colonized the earth to the extent thatplant life now does. Some habitats would have been tough for the ill-adaptedplants to survive. The evolution of trees, though, changed things completely.These new trees differed from other plants by a key adaptation called secon-dary growth. This is the process by which a specialized tissue called cambiumcontinuously grows, adding girth to the stem and roots of a plant. This iscrucial for the growth of trees because the new cambium cells that areproduced each year will become either wood or tissue through which the treecan carry water and nutrients.

Thanks to this ability to grow thicker and stronger as well as a better vascu-lar system, trees were able to grow much, much taller than their ancestors.Plants that can grow taller can grow free from competition for light and thusgrow yet further. The ability to grow taller than other species gave trees a hugecompetitive edge, leading to such great success, evolutionarily. The appear-ance of trees on earth therefore sparked an evolutionary race for size and domi-nance that eventually resulted in the green planet we see today.

Early trees could grow tall, but would not be familiar to us today. Theywould not have had recognizable leaves, but rather thin, whippy branchletsthat would have been capable of photosynthesis. These trees also had veryshallow roots. The next significant change in trees was the evolution of fern-like leaves that were better at capturing light. This occurred some 370 millionyears ago and is seen in the conifer ancestor Archaeopteris. At the same time,Archaeopteris evolved deep roots to get at hard-to-reach water and nutrients,allowing it to colonize previously uninhabitable environments. Again, thiswould have given these advanced trees a great competitive advantage, allowingthem to colonize areas inhospitable to other plants.

Following these significant periods of plant evolution, trees are todayamong the largest living things on earth and represent one of the most sophis-ticated natural structures. Modern Sequoia trees can stand at over 330 feet(100 m) tall with a 100 foot (30 m) circumference, weighing some 1,800 tons.Trees can grow to such tremendous sizes thanks to a process during secondarygrowth called lignification. As a tree grows from a seed, the stem is initiallygreen and very weak because there is nothing but cellulose in the cell walls toprovide support. As the seedling grows into a sapling it quickly outpaces thestructural support provided by cellulose. At this point, lignin, a very complexpolymer molecule, begins to get laid down in the cell walls of the growing tree.This lignin forms the bulk of the woody part of the tree and plays an importantrole in mechanical support, water transport, and disease resistance.

A key role for the woody part of the tree is in the support of the delicatewater- and nutrient-carrying vessels. In non-woody plants and in young trees,two types of vessels are involved in water transport, xylem and phloem. As treesgrow much larger, though, only xylem is involved with the long-distance


transport of water up the massive trunk. Xylem vessels are dead cells with alarge empty space in the middle for water to pass through. Water is draggedup the tree under tension, so the xylem cells are under constant threat of cavinginward. It is the thick layers of lignin in the xylem cell walls that gives the cellsstrength enough to withstand these pressures.

Physically, then, trees are able to grow very tall. Deep roots anchor these mas-sive structures as well as draw up essential water and nutrients from the soil. Buthow do trees draw water up to heights of nearly 100 meters? It was first thoughtthat water, and the nutrients dissolved within it, was drawn up by capillaryaction. This is the property of the forces that are created between water mole-cules that sees them being drawn up narrow tubes. You can see it happen innarrow drinking straws. The water inside the straw will be a little higher thanthe water level in the glass. In very narrow tubes, water can be drawn up muchhigher, although eventually the forces drawing water up the tube will be can-celled out by gravity. It is now known that capillary action will only draw waterup a tube the thickness of a xylem vessel to a height of 3–33 feet (1–10 m)(depending on the type of xylem), still some way short of the tree tops.

Therefore, another force that either sucks or pushes water up the xylemvessels must exist. Evidence shows that it is the former of these possibilities.The cells in a tree’s leaves are packed with water. The air surrounding atree’s leaves, on the other hand, has very little water at all. There is a strongdifferential in water potential between a leaf and the surrounding air, sowater is drawn out of the leaves by the process of evaporation. With waterbeing drawn from the leaves to the air, there will be less water in the leafcells than in the stem cells behind them. Water is therefore drawn fromthe stem to the leaf.

This effect—called transpiration—occurs all the way down the tree, withwater being dragged up from the roots to the leaves. This is why water in thexylem is under tension—it is being sucked upward rather than being pushedfrom behind. What’s more, the cohesive nature of water (thanks to the forcesthat produce the capillary action effect) means that it will cling to the xylemwallsand will not be dragged back to earth under the full force of gravity. As a result,less force is required to suck water up the huge distances of a tree. Calculationsby botanists show that the water pressures in a tree mean that water can bedragged some 380 feet (115 m) upward—exactly the height of the tallest trees.


The wood produced by cambium cells during secondary growth is one ofthe most important materials used by humans. Different trees produce differ-ent types of wood, thanks to their different sizes of secondary xylem cells.Trees like conifers produce versatile softwoods, whereas the huge deciduoustrees of the rainforest produce dense hard woods. Even the super-light balsawood has a number of uses for its insulation and buoyancy properties.


Engineers are even designing artificial trees based on what they know fromreal ones. The aim is that they could be used to extract and purify water fromeven the most arid soil. The process of transpiration where evaporation atthe leaf drags water all the way up the tree is being mimicked in these artificialtrees. The key has been to find a membrane that can be used at the top thathas the same properties as a leaf. Now such a substance has been found, a‘‘hydrogel’’ that has tiny pores within it just the right size to allow the correctlevel of evaporation.

BIRD NESTS

Perhaps the most familiar structures built by animals are the nests created bybirds. Across the globe, birds construct a wide range of nests in which to laytheir eggs and rear their young. Although relatively common, there is a greatdeal of care and craftsmanship that goes into constructing even the simplestnest. Nest-building behavior is an important adaptation that is only part ofthe huge amount of energy adult birds invest in rearing their young. At theirsimplest, bird nests are places in whichto lay eggs and feed young, but in manycases they are much more than that. Thebasic nest design has been honed,through evolution, to give rise to someof the most remarkable structures seenin nature. For some species, nest buildinghas even evolved into an art form.

There is great diversity in the nestingbehaviors of birds. These structures canrange from simple scrapes in the groundto extensive, multi-chambered construc-tions that can be fully weatherproof andwhich can survive for several years. Thesimplest nests are little more than a hap-hazard cluster of vegetation, twigs, andstones. Ducks, geese, swans, penguins,and storks often build only rudimentarynests, which are just enough to raise theireggs from the ground to protect themfrom predators or natural events likeflooding. Simple though they may be,even these nests offer a competitive edgeto the young that might suffer withoutsuch a structure to grow up in.

One of the more spectacular of thesehaphazard nests is that made by the


The intricate nest of the Baya weaver bird,Ploceus philippinus. The nest is enclosed witha tunnel entrance below to protect the eggsand young from predators. [E. HanumanthaRao / Photo Researchers, Inc.]

golden eagle (Aquila chrysaetos). This magnificent bird will heap up vegetationto support its eggs and young. The location an adult chooses for this messynest is right on top of last year’s nest. As these birds can live up to 30 years inthe wild, that can be a lot of vegetation piled up. Over time, these structurescan reach up to a ton in weight. For this reason, the golden eagle chooses tonest on rocky crags, which are able to take this massive weight as well as offerprotection from even the most nimble of predator.

Birds of prey such as eagles and hawks have also been known to adorn theirnests with green sprigs of foliage. There have been some reports that this issimply for aesthetic purposes, not least because they continue the behavioreven when their young have flown the nest. But there seems to be a much moreimportant function of this aspect of nest building. Many trees have evolved theability to produce insecticide poisons to deter herbivores. Hawks and eaglesappear to choose leaves that are particularly high in these poisons. The netresult is that potentially disease-carrying insects are repelled from their nests,thus protecting their young. Other bird species line their nests with feathersfor a similar reason. Their features have antibacterial properties that helpsprevent disease.

Some of the more familiar nests are cup-shaped. Birds like the song thrush(Turdus philomelos) and crows (Corvus corone) build this type of nest from twigs,leaves, mud, feathers, moss . . . almost anything that can be found. Cup-shapednests offer more protection than the more haphazard versions and are moresecure. Their walls prevent eggs from rolling out of the nest, which is crucialfor those nesting high in trees. Other species take this design further andenclose the cup with a roof, which affords further protection from both preda-tors and the elements. The long-tailed tit (Aegithalos caudatus) builds a veryintricate and solid nest that is also well camouflaged by the careful applicationof lichen to the outside. Perhaps the most impressive builder of domed nests isthe Hammerkop (Scopus umbretta). Over 8,000 twigs go into the constructionof this nest, which can be as large as 6.5 feet (2 m) high and 6.5 feet (2 m) wide.This nest has a long entrance tunnel to deter predators and is strong enough towithstand the force of a full-grown man walking over it. This may seem like anover-elaborate structure, but again the adaptation of nest building has evolvedto ensure that offspring have a high chance of survival and so the adaptationcontinues to survive.

All nests require skilled construction, but the most impressive nest-buildingskill is shown by the weaver birds of the Icteridae and Ploceidae families. As theirname suggests, weaver birds carefully weave their nests from long blades ofgrass. These intricately crafted nests are built hanging from a branch or twig.This choice of location, coupled with the enclosed design with a droopingentrance tunnel, effectively keep predators away from the precious eggswithin.

Protection of eggs and young is the primary function of nests, but theweaver bird nests also serve another function. Given that their construction


takes painstaking skill and precision, they provide an excellent signal of itsbuilder’s abilities. Males will build their nests in communal trees before theyhave mated. Females will choose who to mate with based on the quality of theirnest. The most skillful males will get the pick of the females. These top-qualitymales will also be able to build more than one nest and so raise more than onefamily. Nest-building is a difficult skill to master in weaver birds. Young malesmay not even get beyond building the basic foundations of the nest andwill attract no mates because of it. By learning from their neighbors, youngbirds will improve their skill and will be better placed to compete for theattentions of potential mates in the future. For male weaver birds, success withthe opposite sex is entirely dependent upon their ability to provide a well-built home.

Other birds use their nest-building skills as a sign of their fitness and quality,even to the extent that the structure they build is not used to house eggs andyoung at all, but only to attract a mate. The bowerbirds (Ptilonorhynchidae) ofNew Guinea and Australia build large, ornate structures to catch the eye of apotential female mate. Size, diversity, and color are the key features of thesebowers. The basic shape is made from towers of sticks and foliage, which actsas a stage for ‘‘treasures’’ collected by the male. Colorful and shiny objects arecarefully placed under the bower, including: feathers (especially blue ones), snailshells, iridescent beetle wing casings and heads, bones, and flowers. Often,foraged man-made objects, such as spoons and car keys, find their way into thedisplay. The largest bower is made by the Vogelkop Gardener Bowerbird(Amblyornis inoratus) fromNewGuinea. It manages to build a bower over 6.5 feet(2 m) tall and 6.5 feet (2 m) across. Not bad for a bird the size of a song thrush.


Bird nests, while impressive structures, are not a patch on even the simplesthuts built by humans, and there seems to be little to learn from them. There isone type of nest, though, that is particularly interesting to some humancultures for a different reason. Swifts of the genus Collocalia build nests entirelyfrom their own saliva. During the breeding season, their salivary glandsenlarge to enable them to produce enough of this remarkable fluid, whichhardens to produce a strong nest. They even make their nest in the pitch darkof the caves in which they roost, finding their way by echolocation. Unfortu-nately, the main predator these swifts encounter is man. These nests are anedible delicacy in China and are used to make birds nest soup, often causinghuge damage to the local swift populations.

BEAVER LODGES

Anyone who has owned a pet guinea pig, rat, or mouse will know thatrodents are prolific gnawers of wood, paper, and cardboard. The tools of


choice from each of these creatures are the two prominent front teeth that canmake light work of hard foods like nuts. Other rodents, like squirrels, use theirteeth to cut through hard obstacles that are in the way of burrows or runs.However, the most impressive use of rodents’ chisel-like teeth is found inbeavers of North America (Castor canadensis), who are able to cut down treesby gnawing around the base in order to make elaborate homes.

The first part of any construction is to get hold of the necessary buildingmaterials. It is commonly known that beavers cut down trees and branches tothis end, but it is less well known how they manage it. Beavers’ teeth, like thoseof all rodents, are rather unlike the teeth of any other animal. Our human teethare composed of a strong material called dentine, which is surrounded by aneven harder material called enamel. Rodent teeth are made up of the samebasic materials, but instead of surrounding the whole core of dentine withenamel, there is only a thick cap of the harder material at the front. At the backof the tooth, the dentine is exposed. Dentine is a hard material, but it is not ashard as enamel. Given the punishment of continual gnawing through hardmaterials like wood, both enamel and dentine will get worn down. Crucially,the dentine, which is less hard than enamel, will get worn away more. As aresult, the tip of a tooth can get sharpened into a chisel-like point, which givesthe tooth the ideal shape for cutting wood.

With the constant gnawing and wearing down of both dentine and enamel,you might think that it would not be long before the whole tooth would beworn down to a stump. This would indeed be the case if it were not for the


A beaver dam and lodge. [Edward Kinsman / Photo Researchers, Inc.]

beaver’s second neat adaptation. Its teeth, like the teeth of all rodents, growcontinually. They get worn away at the tip, but more dentine and enamel arelaid down at the root, so the tooth stays the same length for the animal’s wholelife. Beavers (and domestic rabbits, mice, and rats) will instinctively gnaw athard materials, even if there is no direct need, in order to prevent their teethfrom growing too long.

So thanks to its ever-growing chisels, the beaver can furnish itself with thenecessary materials to build its home. The beaver feeds on leaves and barktrees and on aquatic vegetation, and so it will live in an area with plenty oftrees with a stream running through it. It is across the stream that the beaverwill build its familiar dam behind which it will build its lodge. The beaverwill drag the trunks and branches felled from the nearby trees to the streamand carefully interlace them to build a sturdy fence across the body of water.The gaps between branches are filled with mud, boulders, and sods of earth,packed in using its front feet to form a near-impenetrable barrier againstthe flow of the stream. Beaver dams are so well constructed that theycan be up to 10 feet tall, built solidly to withstand the pressure of waterbehind them.

Once the dam has been constructed, beavers will build themselves a lodgein which to live. This is typically located in the middle of their artificial lakewhere a small hillock (typically some 10 to 13 feet (3–4 m) wide) has beensurrounded by the rising waters. The beaver will dig a tunnel into thismound from below the water line. From this entrance tunnel, the mound ishollowed out to make a snug burrow. For added insulation, the chamber islined with mud and rushes. Within the lodge there will tend to be twochambers—a wet room for drying off after entering from the water and adry chamber where the family will live. In the absence of a suitable hill inthe lake, lodges can be built from scratch or as part of the dam itself. As withthe dam, branches form a scaffold around which boulders, smaller branches,and mud is packed to make a watertight wall within which chambers can bebuilt and insulated. Once the basic lodge is finished, the beaver will build afew extra features. More entrances are added so they can escape quickly ifthreatened by predators. Further tunnels and vents allow for a complexsystem of heating, ventilation, and air-conditioning to ensure perfect livingconditions inside.

The lake and canals constructed by the beaver act as a protective moat,which allows them to reach their feeding places in relative safety. Even whenthe lake freezes in winter, beavers can survive by feeding on submerged logsand vegetation that have been trapped by the rising waters of the artificial lake.Beavers will even cut leafy branches and stock their lake before winter comesprecisely for this purpose. For some parts of winter, then, beavers can survivewithout leaving their dammed lake. Their lodge provides warmth and shelter,and the lake provides food. Much like humans, beavers have evolved a success-ful adaptation that alters their environment to their own ends.



The beaver’s skills at constructing a home are very similar to many of theearly log-cabin homes built by humans, although perhaps a beaver lodge hasa few more features to ensure that the air inside is fresh and warm. Humanbuilding techniques have moved well beyond this, and there is little to learnfrom the beaver. Its lake-forming behavior is an important one for humans,though. They are important for renewing and refreshing streams that mayhave become silted up, and they create an important wetland habitat for manybirds and plants. Even when the pond dries up and turns to marshland, thenwet meadow, the habitat supports many rare species. Although inadvertently,the beaver is one of nature’s conservationists.

BEE NESTS

Bees are most familiar to uswhen they make their nests in spe-cially prepared hives, allowing beekeepers to harvest their honey. Ofcourse bees do not just live inman-made hives. Although a fewbees build freestanding nests, mostspecies will adapt a suitable hollowfor their home. This hollow is thenadapted using two key buildingmaterials made by bees: wax andpropolis. Wax is a strong but malle-able material that is secreted fromglands on the bee’s abdomen. Thebees will mix the secreted wax withtheir own saliva to make it moreworkable. Propolis, on the otherhand, is not produced by beesdirectly, but has to be collectedand created. It is a more sticky sub-stance than wax and is made fromthe saps and resins collected fromplants by foraging bees. It has avery strong antibacterial andantifungal property and is used tohelp prevent disease spreading inthe nest.

The nest is built to regulate thetemperature inside to as near


A honeybee nest with brood cells layered to helpmaintain a constant temperature needed for thedevelopment of the eggs, larvae, and pupae. [GeorgeD. Lepp / Photo Researchers, Inc.]

optimal levels as possible. Honey bee colonies are able to keep the tempera-tures of their nest at 95–97°F (35–36°C) even when surrounding temperaturescan fall below freezing or soar to over 113°F (45°C). The consequences of notkeeping the nest at the appropriate temperature can be very dangerous. Adultsand larvae alike can be killed off by the cold, and fungi can infest the colony ifthe temperature is allowed to get too high. The ability to regulate nest temper-ature is therefore a crucial adaptation.

Bees are very choosy about where they build their nest. Some honey bees usetree hollows or abandoned animal burrows, which offer not only physical protec-tion but also insulation. As the bees inhabiting the hive generate body heat,further insulation around the hive helps keep this heat trapped inside even in coldconditions. The amount of heat produced by the bees can partly be controlled bythe bees themselves. To raise the temperature of the nest they can rapidly con-tract their wing muscles, generating body heat. So as not to cause damage to thewings by beating them in an enclosed space bees can detach the wing from themuscle beneath. The muscle contracts, but the wing does not beat.

Once a suitable site has been found the nest itself must be built. In manystingless bees there are four key layers to the nest. First, the outer wall of thenest is lined with batumen (meaning ‘‘wall’’), a mixture of wax and propolis.In addition to protecting it from bacterial and fungal attacks (thanks to thepropolis), batumen provides an effective insulating layer designed to keep heatwithin the hive. The batumen seals the nest except the entrance and, in somecases, ventilation holes. The next layer within the batumen lining is a layer ofstorage pots for pollen and honey. This is made by a substance called cerumen,which is again made from a mixture of wax and propolis. Within this layer ofstorage pots is the third layer—the involucrum. This is made with thin leavesof cerumen joined to each other and to the storage pots. The involucrumencloses the fourth layer—the brood comb.

The involucrum is very important for temperature regulation. Stingless beesin cooler climates build more layers of the involucrum than in warmerclimates. These layers act as baffles that inhibit convection currents fromforming within the nest and convecting heat away. Like the other two layers,the involucrum is also an effective insulator. Although only 1 centimeter thick,the temperature on the brood side of the involucrum can be 10°F (5°C) higherthan on its outer side.

The brood comb within the involucrum is the heart of the nest. This iswhere the queen will lay her eggs and where the larvae hatch and grow andeventually molt into adults. Each larva is provided with its own, perfectlyshaped crib. Wax is used to mold a series of hexagonal cells to produce theclassic honeycomb shape. Within each cell, one egg is laid so each larva willgrow in its own wax pen, being fed by the industrious adults of the colony.Not all cells are reserved for larva, though. Honey bee colonies will stock somecells with honey and pollen and use them as a food store with which to feed thegrowing larvae.


Even the brood combs are carefully arranged in order to help control thetemperature of the nest. Closely packed, matrix arrangements of brood cellsallow for heat generated by the developing larvae to dissipate easily. This isseen in stingless bee nests in very warm climates where overheating could bea problem. Nests of stingless bees in cooler climates have a looser arrangementof brood comb cells joined together in a spiral. This spiral design efficientlyconserves the heat generated by the brood.

Key to temperature regulation is having a suitable flow of air through the nest.The design of the comb and the size and location of the entrance hole determineshowmuch air can flow over the brood comb. However, the cooling current of airflowing through the nest is not just caused by the nest architecture. The beesthemselves can help the rate of cooling. All species of bee use their wings to fanthe nest and create airflow in one direction, typically out of the entrance holeor the ventilation shafts, in order to move heat out of the nest. Some species alsouse a water-cooling approach to dissipate heat from the waxy structures of thenest. Individuals will carry drops of water in their mandibles and place them inempty cells in the brood comb and allow them to evaporate. Individual bees willeven smooth the drop of water into a thin film over the comb using their probos-cis (a tongue-like organ) in order to allow for more rapid evaporation.

The careful design of a bees nest not only provides protection for the colonybut has evolved to be a sophisticated structure that keeps near-constant temper-ature. This has proved critical to the success of these social insects who wouldotherwise be very much at the mercy of wildly fluctuating environmental condi-tions. The intricate architecture is achieved by the teamwork of individuals withvery small brains, which is in itself remarkable. Blueprints for the design arehard-wired into bees themselves, although there is also further control throughcommunication between the individuals of the colony, mostly from the queen,using pheromones and sound. Through these simple controls evolution hasproduced a highly advanced solution to the problem of survival.


The basic building materials of bees nests, propolis and wax, are used oftenby humans. Beeswax is used as a sealant and as a polishing agent for woodfurniture. Propolis can be found in many health food stores for its antibacterialproperties. And of course, the honey stored in the nests are a sugary treat forhumans the world over.

PAPER NESTS

As with all social insects, wasps are capable of producing some very impressivestructures. Whereas termites use mud to construct their mounds and bees usewax and propolis to build their nests, nest-building wasps have evolved to maketheir homes from paper. Although it doesn’t sound like a particularly useful


material, wasps’ ability to make andcraft paper has allowed them toflourish. It is a very versatile materialand can be used to make large struc-tures. The largest wasp nest onrecordmeasured 12 feet (3.6m) longwith a diameter of five feet and nineinches (1.7 m). As with bees, thereis great diversity in the nests that dif-ferent wasp species produce.

Paper is produced from well-chewed wood fibers. One of themost skilled workers of the materialare the paper wasps (of the Polisti-nae sub-family), which are found all over the planet in both tropical and tem-perate climates. As with any home, wasp nests need a good foundation. Paperwasps tend to build their nests to hang from a thin stalk attached to a branch.Unfortunately, this location is easily accessed by ants, which will attack thenest to eat the eggs and young. To protect against potential ant attacks thewasps will cover the supporting stalk with a shiny, black secretion from theirabdomens, which is sticky and stops potential invaders in their tracks. Thusprotected, the wasps can get on with making the nest.

The paper for the nest is made from fibers of dead wood, which is chewedand mixed with saliva to make a papier-mache. When wet, this papier-machecan be moulded into the classic hexagonal shapes of the cells that will housethe wasps’ young. The first generation of the nest is the work of just onefemale. After mating she will find an appropriate site, collect the wood fibersfor the paper, build the nest, and tend and collect food for the larvae that hatchfrom the eggs she has laid. Once these larvae develop into adults, though, theyemerge as workers that look identical to the founding female but which are notcapable of reproduction. The workers will then take on the tasks of collectingmore wood fibers to make more paper to extend the nest. They will also foragefor food and attend the developing brood of young.

As with bees, wasps take careful consideration over where to build the nest.It will be ideally located to ensure the nest does not get too hot or cold. This isparticularly important for the nests of the paper wasps because the cells of thebrood comb are open to the elements, although some empty cells are con-structed around the edge of these nests to act as a layer of insulation—this isknown as the functional envelope. Other wasps, such as hornets of the Vespinaesub-family, build enclosed nests and have evolved to build various structuresthat help warm or cool the nest. As with bees, the size and shape of the broodcomb are critical in maintaining the ideal temperature for the developing lar-vae inside. Wasps can also increase the nest temperature by vibrating theirthorax muscles and lower it by fanning it with their wings. However, there


A wasp nest made from paper. [Mark Boulton /Photo Researchers, Inc.]

are other neat adaptations that help not only to strengthen the nest but helpregulate its temperature.

A key ingredient of the paper is the wasp’s saliva with which it makes apapier-mache from wood fibers. The wasp saliva contains a polymer, whichacts almost like a glue, that sets as a very hard material when it dries. Clearlythis gives a direct strength to the paper, although it has another property thatis critical for temperature regulation. The saliva polymer has a certain thermo-electric property that is able to generate and absorb heat to ensure that thebrood comb maintains a certain temperature when the surrounding environ-ment is too cool. When the surrounding temperature gets too high the salivapolymer works in reverse. It loses heat in the form of a slowly discharging elec-tric current. This way, the nest can remain at a near-constant temperature.

The larvae that grow within the hexagonal paper cells produce silk, which hasa similar effect.When they pupate—that is, undergo ametamorphosis to becomean adult—they will spin a silk cocoon around them. This silk has a thermoelectricproperty that absorbs and holds heat when temperatures are high and releases itwhen temperatures are too cool; thus it can help maintain a constant tempera-ture. Critically, though, this constant temperature is higher than that maintainedby the saliva polymer of the adults because the pupa requires a higher tempera-ture (1–3°F [1–2°C] higher) to develop into an adult than is normally requiredfor the growing larvae (around 85°F [29°C]). Intriguingly, it seems that the elec-trical property of the silk can also help the developing pupa communicate to theadult wasps if it is too cool. Adults are attracted to certain cells and will vibratetheir muscles to warm them up. Both pheromones and electrical signals arebelieved to be involved in coordinating this remarkable behavior.


As with termites, architects are exploring the paper structures of wasps tomake improvements to building designs in order to allow a cool supply of airto flow through them. That is in addition to the inspiration derived fromobserving the paper combs of the brood chamber, which are both lightweightand strong. Building supporting structures from man-made structures in thesame way similarly saves weight without any loss of strength. Such structuresare also more flexible, which can be important for certain designs. The honey-comb structure can be found in materials used to make many things fromsquash racquets to engine parts.

CORAL REEFS

The oceanic reefs produced by the organisms known as corals are the largeststructures produced by any living thing. They are so enormous that islands canform on them, ships can run aground on them, and they can support entiremarine ecosystems. The Great Barrier Reef off the east coast of Australia is


composed of at least 400 species of stonyand soft coral, forming a home for morethan 5,000 species of mollusks and nofewer than 1,500 species of fish. It is com-posed of a multitude of coral colonies.The structure we see today is thought tobe 6,000–8,000 years old, although themodern structure has developed on amuch older reef system, thought to be500 million years old. This enormousreef is over 1,250 miles (2000 km) longand covers more than 185,000 squaremiles (300,000 square kilometers), and itcan be seen from space.

These immense structures are thework of countless tiny individual organ-isms called polyps, each no more than afew millimeters in length. By extractingcalcium minerals from seawater, eachpolyp is capable of producing its ownhard skeleton, which contributes to thegrowing reef. Some coral polyps, calledstony (or true) corals, use calcium car-bonate to produce hard, external lime-stone shelters. Other coral polyps usethe calcium mineral building blocks tomake internal skeletons—these polypsare called soft corals. It is the hard coralsthat contribute most significantly to thegrowing stone structure.

Over decades, centuries, and millennia, successive generations of polyps laydown layer after layer of calcium carbonate. As one polyp dies, another willgrow over its predecessor’s limestone shell and will grow its own skeleton. Areef, then, is a huge structure covered with a thin living veneer on its surface.Coral polyps are small creatures, and yet the rate of growth achieved by acolony of these minute organisms is quite rapid considering they are secretingrock. Some of the branching corals can grow in height or length by as much as4 inches (10 cm) per year (about the same rate at which human hair grows).Other corals, like the dome and plate species, are more bulky and may onlygrow by 0.1 to 0.8 inches (0.3–2 cm) per year. This may not seem like much,but it can be sustained for thousands of years, forming huge and complex reefs.

Coral reefs are not only structural wonders of the natural world; they alsooffer a multitude of hiding places for a wealth of marine creatures. The coralpolyps themselves feed by using their short tentacles to trap tiny particles of


An individual hard coral polyp (Tubastrea sp.). Thepolyp will secrete a protective calcium carbonateskeleton, which will help form a coral reef. [PeterScoones / Photo Researchers, Inc.]

edible matter that drift on the ocean currents, and many other creatures whichtake up residence on the reef feed in the same way. Coral polyps also have asymbiotic relationship with a special type of algae, called zooxanthellae, thatlive inside their bodies. These single-celled organisms use sunlight and carbondioxide to make energy by photosynthesis, a process that produces oxygen andother nutrients needed by the coral polyps. In return, these zooxanthellae areprovided, by the polyp, with protection and carbon dioxide.

Coral polyps have another impressive adaptation to help their survival onthe reef. Although they are capable of sexual reproduction, for the most partnew polyps are produced asexually. That is, a new individual is budded fromanother. Consequently, they have exactly the same genes and so would benefitfrom helping each other out. Despite being a simple creature, certain coralpolyps from the same stock can recognize each other and transfer carbohy-drates and proteins to each other when one is in some way damaged. A reef isnot just a collection of individuals living in proximity; it represents a truecolony with communication and interaction between each polyp. With theway that the polyps interact, a reef can almost be thought of as one hugeorganism in its own right.

The coral polyps that can extract food from the ocean are a big draw forpredatory animals such as starfish and parrotfish, whose tough lips can with-stand the hard, sharp protective shell of the coral. In turn, these predators arepreyed upon by larger animals and so on, until a huge variety of organismsare dependent on the reef. In short, a large coral reef represents probably themost diverse ecosystem in the ocean. They are comparable in some ways tothe tropical rainforests on land.

Everything about coral reefs is made possible by the tireless deposition ofrock by a minute sea creature. Individual coral polyps may be small, but as agroup there can be few if any organisms that can match them in terms of theirbuilding abilities. Reefs can become so enormous that they disrupt and divertthe ocean currents. Impeding and diverting these currents has important impli-cations for life in the sea and on land as these streams of water channel heatenergy around the globe, and changing their course can influence weather pat-terns all over the world. Indeed, this modification of the environment directlybenefits the reef-making polyps. The reef can dissipate the huge amounts ofenergy that can be carried in large waves that sweep from the middle of theocean to the shore. This makes the waters around the reef much calmer thanthey otherwise might be, which means that the fragile polyp can grow withoutdamage from the ocean, making the reef a very successful adaptation indeed.


There is no doubting the importance of coral reefs as significant ecosystemsand as important physical structures that can influence the climate of the entireplanet. But can we really learn anything from tiny bricklayers? It seems that wecan. In the past few years, it has been discovered that coral communities may


contain valuable medicines that may one day lead to treatments for cancer andHIV. A recently patented and licensed chemical called eleutherobin is pro-duced by the soft coral Eleutherobia, which has a feathery appearance. Thischemical is able to bind to tiny structures called microtubules that are foundinside human cells. By binding to them, eleutherobin makes the microtubulesvery rigid and prevents cancerous cells from dividing and multiplying.

LUMINOUS GNAT TRAPS

There are many examples of highly elaborate structures built in nature. Thisis the culmination of many small steps in evolution resulting in a highly spe-cialized skill that certain species possess. Although undoubtedly successfuladaptations, these elaborate structures take time and energy to build and mayoften leave their builders vulnerable to attack by predators during their con-struction. In some respects, therefore, the simplest designs can be consideredsome of the most effective. Simple structures have the benefit that they canbe built and rebuilt again and again with little effort or energy.

A good example of a simple, but effective structure can be found in the pitchdark limestone caves of New Zealand. The walls and ceilings of these caves arehome to the tiny larvae of the gnat, Arachnocampa luminosa. The larvae them-selves are not much to look at. They are typically maggot-like, pale in color,and measure around 3 cm long. They have a hard cuticle over the head thatlooks like a brown helmet. Despite their appearance, these unassuming larvaehave a rather dazzling method of finding food.

Arachnocampa larvae feed on other insects to get the protein they need togrow. For a slow-moving larva that cannot see well in the dark, flying insectswould ordinarily prove too difficult to catch in a pitch black cave. Their solu-tion is to stay put and lure their prey to them, and they do this by light. To cre-ate the light, larvae build a simple structure from materials made in their ownbody. It is a simple design and works as both a lure and trap, meaning the larvaneeds do very little to get its food.

After hatching from the egg laid by the adult on the roof of the cave, thelarva first builds itself a hammock from silk produced by a silk gland locatedon its head. Once safely secured in its hammock it makes more silk, whichhangs in threads down from the hammock. As a larva lowers the threads it willexude a small drop of mucus at regular intervals. Once complete, the thread ofsilk with its droplets of mucus resembles a string of pearls, which can be up to14 inches (40 cm) in length.

Excreted within the mucus are chemicals that cause the mucus to glow.Common with other instances of bioluminescence in nature, the light fromthe gnat’s mucus is created by the reaction of the biological molecules luciferinand luciferase. This gives the beads of mucus a faint, blue-white glow. Withhundreds of these luminescent gnat larvae living together, the roof of the caveresembles a starry night sky, precisely the effect the larvae are after to catchtheir prey.


Not many insects call these dark caves home, and those that do venturethere do so by accident. For instance, the larvae of some flies (such as the may-flies and caddis flies) live in water. These can be swept into the caves by thestreams that flow through them. When they hatch and emerge from the waterthey find themselves in the pitch black, not at all the environment they hopedto be in. In normal circumstances, these small flies would head into the nightsky toward the stars. Of course, the stars are not visible in the caves, and theymake the easy mistake of flying instead toward the pinpricks of light on thecave roof. Like a moth to a flame, these small flies soon discover that the lightis not starlight at all, but the deadly, sticky mucus of the luminous gnat. As theystruggle, the flies soon become inexorably entangled and their fate is sealed.

As well as being very sticky, the mucus beads on the thread are mildly poi-sonous. Like the venom of a spider, this helps to quickly subdue the prey soit can’t wriggle itself free. The effect seems to be almost instantaneous. As soonas an insect becomes caught it ceases to struggle immediately. The brief pullon the thread from the struggling insect is enough for the luminescent gnatto identify which of its several threads has caught something. It will then moveover to the appropriate thread and begin to consume it, reeling it back towardit until it has dragged its prey up to its hammock. This means that as well asgetting its insect meal, the luminescent gnat can recycle the silk and mucus itproduced earlier. After eating, the larva will lower another sticky, glowingthread and wait for another unwitting fly to stray into its trap. Very simple,but very effective.

The larvae will eat anything that finds its way into their traps, even adultluminescent gnats. To avoid this fate, the adults tend to move away from lightto prevent accidents. The gnat larvae do extremely well with their simple lureand trap, using it to exploit a habitat where hunting is all but impossible. Theyare an excellent example of a species being successful by making a simple buteffective structure.


As with all bioluminescent organisms, the luciferase-luciferin reaction holdsa great deal of interest for producing highly efficient ‘‘cold’’ light that does notlose energy as heat. All man-made light sources lose a high proportion of theenergy that powers them as heat. The reaction of luciferase and luciferin con-verts nearly all the energy of the reaction into light—none is lost as wastefulheat. This reaction is already used in man-made glow-sticks, but the aim is touse it in a wider range of applications.

NAKED MOLE RAT BURROWS

The structures built by many animals are relatively simple in function.They tend to provide temporary shelter or a place in which to rear young.


Other animals, though, build homes thatare much more integral to their wholeway of life, even to the extent of shapingthe evolution of the species. One such ani-mal is the naked mole rat, Heterocephalusglaber, which spends nearly its entire lifeburrowing below ground.

Neither a mole nor a rat, the naked molerat represents a unique niche among therodents. It is a rather ugly looking creature.Its body is well adapted for burrowing andliving underground and so has evolved to behairless, short-limbed, and practically blind.Their front teeth are enlarged for scrapingaway at the hard soil, and their bodies arecovered in sensitive whiskers and hairs to feeltheir surroundings. The teeth actually growthrough the naked mole rat’s lips so it cankeep its mouth closed when it is burrowing.They live nearly their entire lives below thebaking surface of the East African deserts.Thanks to this way of life, within their tun-nels they have evolved a social way of livingmore akin to social bees and wasps than torodents or other mammals.

The naked mole rat burrows through thesoil in search of subterranean tubers (roots packed with carbohydrate) on whichit feeds. Individuals increase their chances of finding its favorite food by search-ing as a group. Food is scarce, and a mole rat on its own would struggle to sur-vive. By searching as a group, when one tuber is found it can be shared amongstthe colony. In fact, the colony will go one step better than this and will activelyfarm tubers. Once one is found and has been partially eaten, the tunnel leadingto it will be blocked to allow the tuber to grow. As a group, the colony cancontinually harvest tubers without relying solely on finding more.

The collaborative nature of naked mole rats is rare in mammals. Nakedmole rats are one of only two mammals (the other being another species ofmole rat) that have evolved what is called eusocial living, which is consideredto be the highest form of communal living. Eusocial organisms are character-ized by having only one or a few individuals responsible for reproduction.The other classes of individual (castes), such as workers, are sterile. Theyalso have several generations living together and cooperate over the care ofthe young.

Most eusocial organisms are insects—bees, wasps, ants, and termites. Theseinsects have evolved this way of life thanks to some unusual genetics, called


A naked mole rat (Heterocephalus glaber)showing the huge teeth used for burrowing.[Neil Bromhall / Photo Researchers, Inc.]

haplodiploidy, which mean that sisters are more closely related to each otherthan to their own offspring so that it makes more sense, evolutionarily, for anindividual to look after a sister than to reproduce herself. (In such species,females are produced as the result of a sperm fusing with an egg, whereas ifan egg is left unfertilized a male is produced. One remarkable result of theresulting genetic makeup is that a female will share half her genes with herdaughters, as with any sexually reproducing organism, but three-quarters ofher genes with her full sisters.) Mole rats do not have this odd genetic makeup,yet they have evolved eusocial living because of the high levels of inbreedingwithin the family group, which tends to remain within its own network of tun-nels. As brothers and sisters are so closely related, more so than the 50 percentrelatedness we see in most other sexual organisms, it makes evolutionary senseto defer breeding and help the family group. The tunnel-based home built bythe naked mole rat has directly led to how the species has evolved.

Within any one colony of about 80 individuals (although numbers can be ashigh as 300), there tends to be one female and one to three males who breed.Offspring will typically grow to become workers, digging new tunnels andmaintaining old ones. Workers will divide up the work, some working to digthe tunnel and others to carry the loose soil away. Some of these workers con-tinue to grow to become soldiers who protect the colony’s network of tunnels,mostly from other colonies of naked mole rat who may try to take over the bur-row. If a breeder dies, a soldier will become sexually active to replace them.While she is still alive, though, the breeding female keeps others sterile bybrute force—by butting those that show signs of becoming sexually active. Itis thought that the stress from bullying can suppress sex hormones, althoughhormones excreted in the breeding female’s urine may also play a role. Thetop female uses these strong-arm tactics to run the colony, often directly push-ing workers to tunnels, which have collapsed, to coerce them into working.

There is even a disperser caste. These individuals have been described bytheir human observers as fat and unwilling to engage in work. It is thoughtthat these lazy individuals are storing energy until they leave the colony.When they do, they will burrow to the surface (the only time a naked molerat will see the sun) and will search for a new colony to join. Above ground,they cannot find food, so their reserves of fat are all they have to keep going.Both males and females can be dispersers, and they are capable of traveling atleast 1.2 miles (2 km) above ground in their quest to find another colony orestablish a new one with other dispersers from other colonies. It is thoughtthat this behavior has evolved because of the benefits of occasional outbreed-ing. The frequency of disperser castes is the result of the benefits of outbreed-ing balanced with the risks of dispersal, which can result in death in thebaking sun of the desert.

The network of tunnels in which naked mole rats live are well designed andcan have specialized functions. Most of the tunnels are built to search for food.Naked mole rats are particularly good at this and can dig a mile-long tunnel in


less than three months—not bad for an animal three inches long trying to getthrough rock hard soil. Major highway tunnels are built in long straight linesand are big enough for two individuals to pass each other. Branch tunnels fromthe main highway to food supplies are much smaller and can only accommo-date one individual at a time. There are also chambers for sleeping, foodstorage, rearing pups, and even a latrine. The latrine is an important room. Ithelps keep the regular tunnels and chambers clear of excrement, but alsoallows all individuals to cover themselves with the particular odor of the group.Being nearly blind, odor is an important way of knowing whether an individualbelongs to the colony or not.

Living in such an enclosed space, naked mole rats have evolved other keyadaptations to survive. With no access to fresh air from outside, the tunnelscan get extremely stuffy with very low levels of oxygen and potentially danger-ously high levels of carbon dioxide. To cope, they have evolved a specializedtype of hemoglobin that is highly efficient at binding oxygen in the naked molerat’s red blood cells. They also have very low metabolic rates, less than half thatof other rodents, which helps them conserve oxygen. In extreme conditions,these adaptations allow naked mole rats to survive, for a few hours at least, inconditions of just 3 percent oxygen. Humans, by comparison, require air with21 percent oxygen to survive.

The nakedmole rat is a unique and unusual animal. It has evolvedmany adapta-tions rarely seen in animals thanks to its subterranean way of life and its homecarved out of the desert soil. Again, these remarkable adaptations have enabledan organism to live in a niche not exploited by others, allowing it to flourish.


The naked mole rat’s ability to withstand the harsh, low-oxygen environ-ment of its tunnels has become of great interest to scientists interested instudying pain. The high levels of carbon-dioxide gives rise to a very acidicenvironment, which the mole rats seem oblivious to. It seems that the nakedmole rat lacks a gene that produces the neurotransmitter that is responsiblefor transferring signals along nerves that would normally detect pain. Scien-tists are exploring whether these neurotransmitters could be disabled inhumans who suffer from chronic pain, delivering much needed relief. Thereis also hope for exploiting the mole rat’s highly efficient, oxygen-grabbinghemoglobin for treating diseases caused by hypoxia (lack of oxygen), such asheart attacks, kidney disease, strokes, cancer, and diabetes.

DIATOMS

In most bodies of water, in freshwater, sea water, and even in soil water,there can be found humble-looking algae called diatoms. Ecologically, diatomsare very important organisms. Although they are very tiny, being made up of


just one cell, there are a great deal ofthem on this planet. There are over70,000 species and, all told, diatoms re-present a significant proportion of thebiomass in our oceans. They are there-fore an important source of food formany organisms. Diatoms and othermicroorganisms that float through theseas make up what we call plankton,which many sea creatures, even whales,feed on. Like all algae, diatoms makeenergy by photosynthesis. Thanks totheir sheer number, this means they pro-duce a significant amount of the oxygenwe breathe. They also absorb and ‘‘lockup’’ a lot of carbon dioxide, effectivelytaking it out of the environment. For allthese reasons, diatoms are known as thetrees of the sea—they really are asecologically important as the plants ondry land.

There is no doubting the importance of diatoms to our planet’s ecosystem.Recently, though, something else has been discovered about them that makesthem even more remarkable. Since they were first discovered and studied undermicroscopes, scientists have appreciated the sheer beauty of diatoms. Thesesingle-celled organisms are encased by a highly ornate, symmetrical, siliconshell, called a frustule. Each species produces it own unique shape—circular,oval, stick-shaped, star-shaped . . . pretty much any shape imaginable. Whateverthe shape, every species produces a shell that comes in two halves that fittogether much like a petri dish or Camembert cheese box. In fact, the name‘‘diatom’’ means ‘‘cut in half.’’ The larger upper half of the shell is called theepitheca, which overlaps the smaller lower half called the hypotheca.

The shells themselves are intricately created from silica, making diatoms thesmallest glass-workers on the planet. The shells are often punctured by manytiny pores and slits, which suggests a function beyond simple protection,although it is not clear what this function might be. Scientists are only begin-ning to unlock the construction of these tiny shells. As more is discovered,there is greater realization that diatoms are truly great master craftsmen.

The main scaffold of the shell is silica, which is produced by the diatomwithin its single cell in what is called the ‘‘silica deposition vesicle.’’ A vesicleis a simple, fluid-filled sac that floats around inside a cell. This hardly soundslike a sophisticated organ to be involved in producing an important bio-material, but it certainly manages to do the job. The silica deposition vesicleis thought to act as a mold in which the frustule will grow. Once silica has been


A scanning electron micrograph of a diatom.Diatoms are single-celled algae that secretean intricate glass cell wall (known as a frustule)for protection. [Eye of Science / PhotoResearchers, Inc.]

produced inside the cell, the diatom must secrete it and build its shell. It is notclear exactly how silica is secreted, although it is assumed there must be someform of silica transporter molecule involved.

Key building blocks for the construction of the silica shell are called silaffins(meaning a molecule with an AFFINity to SILica). Silaffins were first discoveredin the diatom Cylindrotheca fusiformis. They are arranged around the diatom’s cellwall and act as a scaffold for the silica to be laid down. Silaffins precipitate liquidsilica that is transported from within the cell into solid silica, which forms thefrustule. It seems that the structure of silaffins allows them to bind together toform a rigid structure around which silica can be deposited.

Silaffins are peptides, short sections of protein made up of fewer than 30amino acids, the building blocks of proteins. From these short sections of pro-tein hang molecular ‘‘side-chains’’ that are made from bio-molecules calledpolyamines. These side chains are of different lengths, and shapes are criticalin how silaffins link together to create the scaffold to produce the unique glasswall of the species in question. The great number of possible combinations ofthese side chains explains why we see such huge diversity in diatom shell shapes.

Although much is known about how diatoms produce such intricate andornate shells on such a tiny scale, we have only scratched the surface. Otherorganic molecules as well as silaffins are likely to be involved in creating thefrustule, but it is not yet known which ones or how they work. This is a fasci-nating field of work that will soon reveal how a simple, single-celled algamanages to be nature’s finest builder of minute structures. What is not knownis the evolutionary significance of this adaptation. It almost certainly is impor-tant in protection, which may explain why there are so many diatoms in ouroceans. However, there are tantalizing hints at a greater evolutionary purpose.


There is a great deal of interest in understanding and harnessing the abilitiesof diatoms to produce such tiny, precise structures. In the future, diatomscould be engineered to exact specifications to create microscopic sieves; toact as gears in microscopic robots; to deliver drugs to specific parts of the bodythrough the bloodstream; or to build tiny diffraction gratings that could beused to produce advanced holograms. Unlocking the secrets of how a diatombuilds its shell could also be scaled up to help designers build strong, but light-weight, structures in aerospace and vehicle manufacture.

Probably the most pursued field in which diatoms are being studied is in thecomputer industry. Currently, nanotechnology techniques that involve build-ing up three-dimensional objects take a painstakingly long time. If diatomscould be engineered to produce silica structures to a design, tiny microchipscould be produced without having to lift a finger. The first step toward har-nessing the nano-construction abilities of diatoms has been taken. In 2004,the first diatom genome was sequenced for the species, Thalassiosira pseudonana.


The trick is now to understand what each of the genes do and to work out howthey can be manipulated. No easy task.

WEBS

Of all the remarkable structureswe see in nature, few can be asfamiliar as the spider’s web. Thereare 40,000 species of spider cur-rently known to exist, and everyspecies uses silk in some way oranother, although not necessarilyto make a web. Webs vary greatlyin size and appearance, but all ofthem are elegant traps for catchingprey—normally insects. Some ofthe simplest webs are nothingmore than a few strands of silk

radiating from a silken tube concealed in a crevice, whereas others are complexarrangements of strands running in all directions.

Visually, the most impressive webs are those commonly known as orb webs,the archetypal spider’s web. The orb web varies from species to species, butessentially it is made up of three elements, all of which require slightly differ-ent types of silk. The core is made from the radial threads that run from thecenter of the web like the spokes of a wheel. Next are the frame threads thatserve as points of attachment for the radial threads and are anchored to wher-ever the spider chooses to construct its trap. Lastly is the catching spiral. It isonly this last element that is sticky and which directly snares the prey. Not onlyis the catching spiral sticky, but it also very elastic. In contrast, both the radialthreads and the frame threads are non-sticky and relatively inelastic. It is notknown exactly how these various parts are linked, but it seems that the orbweb spiders produce a type of glue to fix the web together at the 1,000–1,500connection points.

Spiders are able to weave their silk in all sorts of ways, making all kinds ofstructures possible. Some species weave their silk into sheets enabling themto make tubes for hiding in and catching prey. The purse web spider (Atypusaffinis) uses its silk to produce a small sock-like structure that extends fromthe spider’s burrow. When an unsuspecting victim strays over the purse webthe female will strike from beneath and stab its prey through the web with hugefangs. Once the prey is dead, the female purse web spider will slit its web anddrag her meal into her lair to eat it. After eating, the remains are discardedand the slit repaired.

The trapdoor spiders use their silk to line a vertical burrow and a small cam-ouflaged lid that fits the burrow entrance perfectly. Radiating from the burrow


The different silks and glues used by spiders to pro-duce webs. [Michael Abbey / Photo Researchers, Inc.]

are a number of silken threads that alert the spider to the presence of prey.When it feels an insect moving near its burrow the spider flips the lid of itsburrow and grabs the unfortunate victim in a lightning-fast lunge. In a similarapproach, the so-called money spiders build what at first sight looks like atangled mass of threads in low vegetation that are often revealed in theirthousands by morning dew or frost. Above the domed sheet web there arenumerous vertical threads, all of which serve to entangle passing insectsthat eventually find themselves on the domed sheet and within reach of theweb’s owner.

Some species of spider even team up to produce huge, three-dimensionalcommunal webs, which can support up to 1,500 spiders living together.Spiders of the Uloboridae family will live together on a single web and willwork together to wrap up prey that falls on to it. Collectively they will pourtheir digestive juices over the body to liquefy their food, but this is wherethe cooperation of these spiders ends and they fight over the prey once ithas been subdued. Lynx-spiders, on the other hand, will cooperate in buildingthe web and in feeding, the adults feeding first and the juveniles afterward.Taking things further, there are several Stegodyphus species that have a highlyevolved social system. They will build a communal web, but this is populatedby only a few members of the group. Most individuals will remain hidden inlairs. When prey falls into the web, the lookouts recruit help by tugging onthe silken strands of the web. The rest of the group will then emerge fromtheir lairs and come to assist, attacking the prey with bites and injectingdigestive juices. Again, the group will feed together, sharing their prize.In one species, though, those that fail to help in making the kill are chasedaway and are not allowed to feed! All these fascinating and adaptive socialbehaviors stem directly from many individuals collaborating to produce asingle communal web in which to live.


Spider silk itself is the subject of a great deal of research thanks to itsremarkably versatile nature, being both strong and supple. However, the waysin which spiders spin their webs is being explored as well. In recent yearsthere have been great leaps taken in the field of nanotechnology thanksto the way spiders spin their silk. The problem faced is that once a newnano-material is produced, it is hard to replicate on an industrial scale—thatis until engineers came up with electro-spinning that draws its inspirationfrom spiders. A tiny nozzle is used to eject the material in question, and elec-trically charged plates are used to direct the flow—not exactly how spiders doit, but a good way of mimicking what these creatures can do thanks tomillions of years of evolution.


6

SENSING THE ENVIRONMENT

SENSING THE ENVIRONMENT—HUMAN INVENTION

Humans have a reasonably well-rounded set of senses. Our eyesight is thedominant sense, but hearing, touch, taste, and smell are all pretty goodtoo—they certainly serve their purpose. None of our human senses, though,ranks highly in nature as being extraordinarily sensitive or acute. Many organ-isms exceed our ability to detect our own surroundings. The inquisitiveness ofhumans, however, pushes us to be able to detect and understand more aboutour environment—our home planet and even the far reaches of the universe.To do this, a whole gamut of devices have been invented over the years toimprove our own senses.

With sight being our dominant sense, there has been a great deal of atten-tion paid to being able to see objects that are too small or too distant for oureyes to detect. The smallest object that the human eye can detect is about thethickness of a human hair, some 100 micrometers (0.0001 meters). Any smallerthan this and we see nothing. Since the sixteenth century humans have beenable to explore the world of the very tiny with the invention of the microscope.

The first simple microscope made use of the glass lens that had beeninvented earlier in the fourteenth century to improve eyesight. The initialdesign placed one or two of these lenses together in a tube. Thanks to this sim-ple design, early scientists discovered much about the cells that make up ourbodies and the intricate structures of everyday objects like cork. Simple micro-scopes, though, were unable to magnify images indefinitely. As the lensesbecome more curved to increase magnification, the image they producedbecame blurred. Various innovations in the nineteenth century corrected theseproblems. For example, placing several lenses together in a microscope, each

with only a weak magnifying power, gives an overall high degree of magnifica-tion with no blurring. These innovations allowed scientists to see even smallerobjects.

The next step from these microscopes, which required an illuminating lightsource to shine either on top of the object being viewed or behind it, was to usethe electron as an alternative light source. Electrons are extremely tiny and canbe fired at miniscule objects that cannot be seen by a light microscope. Theway the electrons bounce off the object can be detected by an electron-sensitive plate to produce a picture. Since the 1930s, electron microscopeshave been used to look at viruses, the tiny organelles within cells, and evenatoms. Electron microscopes are able to magnify objects by up to 1 milliontimes their actual size.

The microscope, in its various forms, allowed humans to explore themicrocosms of the planet and understand in much greater detail the life thatlives there. However, humans have been equally curious about exploringobjects very far away from us—objects in the far reaches of the universe.The history of the telescope is much like that of the microscope. A simplearrangement of a convex lens at one end of a tube in association with a con-cave lens at the eyepiece allowed light from distant objects to be magnified.This initial design, built in the sixteenth century, could magnify objects byonly three or four times their actual size. But in the early seventeenth centurythis basic design was improved by Gallileo to achieve magnification of20 times. It was with this telescope that Gallileo mapped the moons and plan-ets of the solar system.

Newton made further improvements to the light telescope in the late seven-teenth century by making use of parabolic mirrors to focus light onto the lens,but it wasn’t until the twentieth century that a significant leap forward wasmade. Humans can see only a narrow band of the electromagnetic spectrum,what we call the visible light or the visible spectrum. Yet objects reflect andradiate other wavelengths of light as well, including ultraviolet or infraredlight. Radio telescopes that could focus and detect radio-waves reflected bydistant objects allowed astronomers to explore and describe objects fromacross the Milky Way. Radio-waves, though, have longer wavelengths andlower energies than visible-spectrum light, so radio telescope antennae needto be very large to capture the radio-waves emitted by objects in space and givea clear resolution. This is why the radio telescope dishes seen in the middleof the desert are so huge. The aptly named Very Large Array telescope inNew Mexico is really 27 large antennae linked electronically to give the effectof a single antenna 22 miles across. Using similar telescopes, infrared, ultravio-let, X-ray, and gamma radiation telescopes are used now to explore the hugeexpanse of space. As yet, there is not one device that can ‘‘see’’ and magnifyeach of these wavelengths of light—for now we must make do with specialisttelescopes and build up a composite picture of the universe from the collectivedata received.


With vision being the dominant sense in humans, much of our inventionsfor describing the environment are based on light. There are, though, usesfor artificial sensors of sound, smells (chemical odors), and touch. Micro-phones are very simple but effective devices that convert sound into electricalenergy. This electrical signal can then be converted back to sound via aspeaker. Microphones work thanks to a thin membrane-like diaphragm withinthe device that vibrates according to the frequency of sound waves passing overit. How the diaphragm converts sound to an electric current depends on whatmaterial it is attached to. All materials used have certain electrical propertiesthat change when they are moved by the vibrating diaphragm, allowing anelectrical current to be generated.

In some microphones a plastic or metal diaphragm is connected to a layer ofcarbon dust. Vibrations in the diaphragm compress the carbon dust, and thedegree of compression varies according to the frequency at which the dia-phragm vibrates. The degree of compression affects the electrical resistanceof the carbon, which can be exploited to send an electrical signal to thespeaker. Other microphones make use of the electricity-generating propertiesof an electromagnet. A magnet moving within a coil of wire will generatean electric current in the wire, so the diaphragm can be attached to either themagnet or the coil so that a current is generated when it moves that corre-sponds to the vibrational frequency of the diaphragm.

Touch sensors have only recently been developed for their use in robotics.There are several types: touch sensors, tactile sensors, and slip sensors.In simple devices, touch sensors can detect whether two surfaces are touchingor not. In more complex designs, they can sense the pressure with which thesurfaces are touching. For the simple design, the sensor can work just like amechanical switch. When two surfaces are pressed together the switch is trig-gered and an electrical signal is sent to a receiver. Pressure sensors rely onone surface being covered in a compressible conductive foam whose electricalproperties change when compressed. This allows a variable electrical signalto be sent to the receiver depending on the pressure exerted. Typically, thematerial used for this is a carbon-infused rubber.

Tactile sensors are used to determine variations in the structure of theobject that the sensor is touching. The analogy is that our human skin can dif-ferentiate between the feel of texture of different objects like wood, fur, water,metal, and so on. Currently, tactile sensors are nowhere near as sensitive totexture as human skin. They work by stringing a series of touch sensorstogether and building up a collective picture of the different pressures exertedby the object at different points. The data collected is generally poor and reliesheavily on the computing power of the receiver to interpret. Slip sensors, astheir name suggests, detect whether two surfaces are no longer aligned.Again, this can be achieved by a series of touch sensors that detect that anobject is moving across them. There are a variety of methods used to achievethe same thing in touch sensors. Currently, though, the aim is to develop a

SENSING THE ENVIRONMENT 139

multi-sensor that can detect not only touch but variations in temperature andso on. Here the inspiration is once again found in nature—human skin, whichis capable of detecting a range of stimuli.

Finally, although there are a great number of applications for a chemical‘‘smell’’ detector, there are very few that have been invented. Indeed, many ofthe detectors in development today draw their inspiration entirely from thechemical detectors that have evolved in nature, and these detectors are coveredlater in this chapter. Perhaps the most well-known detector used by humanswas the canary in a cage, which miners took deep underground to check forodorless gas. Gas pockets could asphyxiate humans, so some form of warningwas essential. Unfortunately for the canary, the birds could not smell the gaseither, so the warning came from the bird being overcome by gas and crashingto the bottom of the cage. Clearly, there is still a long way to go, and evolutionhas a lot to teach us.

VERTEBRATE EYES

The animal kingdom is domi-nated by visual organisms. Thepicture that animals, humansincluded, build up of the world isproduced by light falling on sensi-tive cells in the eye, which is inter-preted by the brain to create animage we see. The brains of ani-mals are excellent at convertingthe information passed to them bythe nerves carrying informationfrom the eye, so the quality of thepicture tends to be determined byhow well the eye detects light.Unlike the compound eyes ofinsects, vertebrates have just two

eyes that are well adapted to absorbing a lot of information that the brain con-verts to a detailed picture of the surrounding environments.

There is a great deal of variation in how well vertebrate eyes do their job, yetthe basic model of a vertebrate eye is the same for all vertebrates. Vertebrateeyes are typically round, with a cornea and lens at the front that lets lightthrough into the main part of the organ. The lens is controlled by muscles thathelp focus the image falling on the light-sensitive part, the retina, which islocated at the back of the eye.

The retina itself is a complicated layer of nerves on top and light-sensitivecells (rods and cones) beneath. Light passes through the layer of nerves andfalls on the rods (which are more sensitive to light) and cones (which are


A scanning electron micrograph of the rod and conephotoreceptor cells found on the retina of the verte-brate eye. [Omikron / Photo Researchers, Inc.]

less sensitive). Humans have a mixture of rods and cones, which allows us tosee in a range of light intensities.

Curiously, the arrangement of the retina in vertebrates is far from perfect.The nerves of the retina all feed into the optic nerve, which transfers the infor-mation from the rods and cones to the brain. However, as the nerves lie on topof the light-sensitive cells, the optic nerve has to pass through them, which iswhy animals such as humans have a blind spot. This makes little difference,as we hardly notice it, but it is far from optimal. Ocean-dwelling animals suchas the giant squid have a retina that is arranged with the nerves behind thelight-sensitive cells, so there is no need for an optic nerve to puncture theretina. Consequently, there is no blind spot for a squid.

Diurnal animals, those that are active during the day, tend to have manymore cone cells than rod cells in the retina.What’s more, they will tend to haveparticularly densely packed clusters of cones in special, small depressions in theretina called fovea. The shape of these fovea allow light to fall on more conesthan normal, which gives better visual acuity than if the retina was smooth allover. They are positioned to give better visual acuity at the center of the fieldof vision, and they are most notable in birds such as hawks, which can seeexcellently from great distances. In humans there are some 10,000 cone cellsper mm2 across most of the retina; in the densely packed fovea there are200,000. Birds like hawks have up to 120,000 cones per mm2 across most ofthe eye and up to 1,000,000 in the fovea! Such a density of light-sensitive cellsallows hawks to produce a clear picture of the environment from a muchgreater distance than humans.

There are other adaptations that give birds such very good eyesight. Theireyes are typically much larger, in proportion, than mammals, which means thatthere is a greater area over which the light-sensitive cells are spread. Further-more, the lens focusses light in such a way that an image is focussed equallywell across the whole retina. This is not the case in humans. The peripheryof our vision is quite blurred, and we need to move our eyes directly towardwhat we want to see to get a clear picture of it. This brings the light from theimage directly on the specialized fovea in the center of our vision. This is notthe case with birds. They can see perfectly out the corner of their eye. Eventhe way that the lens is manipulated by muscles to focus an image is animprovement on the eyes of mammals. Muscles attached to the cornea allowit to bulge outward, something which mammals cannot do, giving a muchgreater focal range.

Birds are not the only vertebrates with specialized eyes. Some animals havewhat is known as a ramp retina. The eyes of these creatures are more oval thanround, which causes the retina to curve in an uneven arc rather than in a regu-lar semicircle. As a result, one-half of the retina is nearer to the lens than theother half, which is a significant adaptation because it means that the eye canfocus on both nearby objects and distant objects at the same time. Horses havea ramp retina. Below the eye-line, nearby objects are in focus; above the


eye-line distant objects are in focus. So when they dip their head to graze theycan look at what they are eating and what is on the horizon, allowing them towatch out for predators and eat at the same time.


Humans have always had a fascination with designing robots that mimichuman behaviors in order to assist genuine humans in day-to-day tasks.A challenge in designing these robots is to design a visual sense that allowsthe robot to detect and recognize certain objects. A robot capable of thisbehavior could be used to help physically handicapped people. The latestwave of robots designed at MIT have eyes that can track objects in the sameway as human eyes and, thanks to the robot’s computer brain, recognizefaces and objects.

In addition to designing eyes for robots, some early steps are being taken todesign artificial eyes that enable visually impaired people to see. Simplecamera-like sensors are built into ordinary-looking sunglasses. Tiny com-puters in the glasses interpret the visual data collected, like our own eyes.These are then sent in electric pulses directly into the brain, exactly like theoptical nerve that runs from the retina. Rather than the brain creating a visualimage, the data from the glasses is converted to sound, which relates to theshape of an image. This is an amazing advance, but clearly there is still a longway to go to mimic eyes that have evolved over millions of years.

INSECT EYES

Flying insects are amazing creatures.Unlike humans who are restricted to mov-ing about on the ground, insects arecapable of moving in three dimensions andat incredible speeds. Like the top fighterpilots who are in control of some of themost speedy and agile machines ever builtby man, insects also need to absorb andprocess a great deal of information to avoidcrashing. Given the relatively vast brain of ahuman pilot, not to mention the variouscomputers, gizmos, and gadgets that arethere in the cockpit to assist, it is remark-able that a tiny insect with a frankly minis-cule brain can perform swoops, dives, andmaneuvers with such consummate ease.

To avoid crashing, the insect needs to beaware of what is going on around it by


A scanning electron micrograph of aninsect eye showing hundreds of individual,rounded ommatidia. [Thomas Deerinck,NCMIR / Photo Researchers, Inc.]

building up a mental picture of theworld. It is little surprise, then, thatinsect eyes are huge organs and that80 percent of its brain capacity is takenup with processing the information thatthey take in. Insects have two sorts ofeyes—simple eyes, called ocelli, and apair of compound eyes. Both are veryimportant to the insect as it goes aboutliving its life.

The simple eyes are just that. Theycan detect subtle changes in light levels,which help the insect keep track of timeand to detect when it is flying undercover, out in the open, or even if a poten-tial predator has loomed over it, castingits shadow. If it is the latter, the insectcan take the appropriate evasivemaneuvers.

Compound eyes are the actual organsof vision. These eyes are very differentfrom our own. Human eyes have a singlelens that projects a tiny image on thelight-sensitive retina at the back ofthe eye. The optic nerve running fromthe retina then relays the data received bythe eye to the brain, where an image is built up. Insect eyes, on the other hand,aremade up of thousands of tiny hexagonal lenses called ommatidia. Each omma-tidium is a long lens that directs light onto a light-sensitive nerve ending at theend. Like our eyes, this nerve sends an image to the insect’s brain, albeit at amuchlower resolution than we see. It is by building up each of these thousands ofimages that the insect can build up an image of what it is looking at.

If an insect were to simply stare at an object it would not be able to see it atthe same level of detail that humans can. So what benefit derives from havingcompound eyes if they do not produce a clear picture? To answer that,we must understand how compound eyes work in seeing moving rather thanstationary objects. Insect eyes come into their own when they are movingabout, which is what insects do a lot of the time. Instead of being sensitive tothe detail of an image, an insect’s eye is very sensitive to movement. A movingobject triggers an image in one ommatidium, then a split-second later triggersan image in an adjacent ommatidium and so on. The compound eye can there-fore build up an idea of a moving object by the wave of images that it createsfrom one simple lens to the next. The same principle applies when an insectis flying around its environment.


A higher magnification scanning electronmicrograph of an insect eye that has been cutthrough to show the long photosensitive cellof the ommatidium, capped with a lens. [Sus-umu Nishinaga / Photo Researchers, Inc.]

As objects pass across an insect’s field of vision, the insect can determinehow close they are thanks to the speed at which they pass them. Because oftheir proximity to the flying insect, the image of nearby objects will passthrough the insect’s field of vision more quickly than those farther away. Thinkof how quickly the roadside fence seems to pass by so much quicker than thetrees in the distance when you are in the car. When you are in the car, though,the nearby objects pass by in a blur and those in the distance are easier to focuson. For insects it is the other way around. The faster an object moves past itsfield of vision, the more clearly it is registered by the insect’s brain. As nearbyobjects pass its eyes more quickly, an insect can build up an excellent pictureof its immediate environment as it flies past. This is critically important forthe flying insect, as it needs to be acutely aware of possible hazards when flyingabout at such high speeds. It is this excellent vision of movement, combinedwith lightening reflexes, that explains why house flies are so hard to swat.

With all eyes, images are built up from a series of short snapshots of thesurrounding environment. This is how a flick book works. Draw a series of pic-tures on the corner of a notebook and riffle through them and it will look like acontinuous moving picture. Human eyes fuse flickering images into a continu-ous one at 15 frames per second. Fast-flying insects such as house flies see indi-vidual images at 100 frames per second. As a result, flies can negotiate complexenvironments at high speed that no fighter pilot would be able to cope with.

The compound eyes of insects are an excellent example of perfect adapta-tion to a particular lifestyle. Insects either need to move quickly themselvesor need to spot fast-moving creatures so that they can move about, hunt, andavoid predators. Human eyes just wouldn’t be up to the job, and the onlyimage we would be able to see would be a blur of movement. For insects, theirlife is based on movement, so they have evolved the right equipment to surviveand flourish.


The compound eyes of insects are greatly interesting to air and naval war-fare researchers. Unmanned vehicles have the benefit of carrying out surveil-lance without risking human life. By mimicking insect eyes, these vehiclescan be piloted much more easily through tricky terrain and can also be usedto build up images of very tiny objects that are not visible with conventionalcameras.

ECHOLOCATION

There is no doubt that vision is an important sense for most animals, butthere are limitations to this sense. Eyes only work if there is some light forthem to detect, which means it can be difficult for an animal to find its wayin the dark. Certainly, there are some nocturnal animals that have evolved


highly sensitive eyes that can see well inthe dark, although these animals still relyon there being some light, even if it isonly the weak light reflected by themoon. Some animals live in placesentirely bereft of light, and they havehad to evolve different senses to findtheir way around. Slower-moving ani-mals might rely on smell, touch, andvibrations, but this would be no goodfor a faster-moving animal—they wouldbump into things far too frequently. Toget around this problem some of thesespecies have evolved to make use ofsound to navigate. Probably the best users of sound in this way are the bats.

Bats are a diverse group of mammals ranging from the bumblebee bat,Craseonycteris thonglongyai (weighing between 0.003–0.004 pounds (1.5–2 g)to the giant golden crowned fruit bat, Acerodon jubatus (weighing 2.6 pounds[1.2 kg] with a wingspan of 5 feet [1.5 m]). Bats are the only mammal to haveevolved true flight and are divided into two distinct sub-orders. The largemegabats (Megachiroptera) feed on fruits, and the smaller microbats (Micro-chiroptera) feed on small insects. Megabats have very good eyesight, whichthey rely on to find their way around. It is the microbats that have evolvedthe use of echolocation to find food and navigate their environment, althoughthey can see a little in dim light. Echolocation in the microbats is so well honedthat they are able to locate and catch tiny insects on the wing, a remarkableblend of the senses and aerial ability.

The elements of echolocation are simple: a sound is emitted and the echosare detected as they rebound from objects in front of the bat. To finely tunethis ability, though, bats have evolved a number of highly specialized adapta-tions. Some bats emit sounds that are audible to humans—you might haveheard these ‘‘ticking’’ sounds when out walking at dusk. These sounds areused by bats to avoid bumping into large objects, but they cannot help thebat detect much smaller objects like flying insects because these audiblesounds have too low a frequency. Low-frequency sounds will simply passthrough small objects, and they won’t bounce back as an echo. Therefore,to locate small objects like insects, most microbats emit very high frequencysounds to create an echo.

These high-pitched sounds are produced in the larynx (as with all mammals)and are emitted through the mouth and nostrils. Many bats have even evolvedmodified noses that are ornate flaps of skin and cartilage. These so-called nose-leaves act as an auditory lens that focuses the bat’s calls into a narrow beam.Bats are able to emit and detect such high-pitched sounds that they can navi-gate around wires only 0.2 mm thick.


The Californian leaf-nosed bat (Macrotuscalifonicus) showing large ears used for echo-location. [Merlin D. Tuttle / Bat Conserva-tion International / Photo Researchers, Inc.]

Once a bat has emitted a high-pitched call, it must listen for the respondingechos. To achieve this, bats have excellent hearing. They have very large earsthat funnel sound into their auditory canal. Their inner ear, too, is welladapted to picking up quiet sounds, having a large, spiraling cochlea that issensitive to a range of frequencies. Unfortunately, a bat’s ear is so sensitive thatit represents a major problem for its owner.

Because high-pitched sounds quickly lose volume as they travel through theair, bats need to call loudly to maximize the distance over which they echolo-cate. Some bats are able to produce sounds that are up to 12,000 decibels—about 100 times as loud as a rock concert! This would be loud enough todeafen anything, not to mention a bat with sensitive hearing, which is why batshave evolved a way of protecting their sensitive ears. Bats can disconnect theirown hearing when they give their ear-splitting calls. There are two tinymuscles in a bat’s ear that are attached to the bones, which connect the eardrum to the inner ear. (Humans have the same bones.) When a bat calls, themuscle disconnects one of these bones (the stapes) from the ear drum, breakingthe connection from the outer ear to the inner ear. This means no sound trav-els to the very sensitive inner ear, avoiding debilitating deafness. Immediatelyafter the call is made, the muscle relaxes and full hearing is restored, allowingthe bat to detect the echo.

A further benefit of using high-pitched calls is that very few animals can hearit. (It is certainly above the threshold of human hearing.) This means thatpotential prey cannot hear the approaching bat. This would mean that batscould hunt with stealth and more or less pick off prey at will, but it seems thatthings are not as simple as that. Some nocturnal moths and some species oflacewing have evolved hearing organs that detect the high-pitched frequenciesused by bats. The ability to hear their predators as they hunt allows these preyspecies to take evasive maneuvers and escape from harm. The story doesn’t endthere, though. It appears that bats have begun to evolve to use differentfrequencies of sounds to hunt, which the moths cannot hear in order to remainhidden from their prey. Bats and insects are locked in an evolutionary armsrace—a constant struggle to find the upper hand over their nemesis.

Whether or not it has been detected by its prey, once a bat has located alikely meal on the wing it will move in for the kill. This is not as easy as it mightsound. Flying insects move quite erratically to avoid being plucked from the airby a predator, so locking on to these weaving insects is tricky. To assist them,bats will modify their calls during the hunt. When searching, they may emitlower-frequency, intermittent calls. Once they have detected something, theywill switch to higher-frequency calls to pinpoint the prey and will begin to callmore often.

Once ‘‘locked on’’ to their prey, the bat will move in. Rather than headingstraight for its quarry, though, a bat will perform a behavior called ‘‘parallelnavigation.’’ It will keep its head pointed at the insect, emitting calls to detectits location, but it will fly toward it at a slight angle. If the insect is located


northeast of the bat, the bat will move so as to keep the insect northeast of it,while gradually closing the distance. This helps the bat lock on to its prey’sposition and predict its trajectory. It will then move on an intercept course tomake the kill. This is exactly how engineers solved the problem of program-ming early guided missiles in the 1940s. Once locked on to its prey, the bat willzero in and intercept it in less than a second.


Bat echolocation is being investigated as a means to help visually impairedpeople build up a picture of what is around them. Devices are being built thatemit ultrasonic sounds like bats and detect the echos as they bounce back.These echos are translated into audible sounds, which are played to the userthrough a headset. Sound is played through the left and right earphonesdepending on where the object is relative to the user, allowing them to buildup a picture of their local environment.

ELECTROSENSE

Thanks to a nervous system based onsending electrical signals through thebody, all animals generate a faint electricfield around their body. In water, thisfield travels further than in air. It is per-haps not surprising, then, that manyaquatic animals have evolved the abilityto detect these electric signals, not tomention the behaviors to exploit it. Elec-tric eels can generate and dischargelethal blasts of electricity, but that is notthe only use of electricity in nature. Theability to detect and respond to electricsignals, especially in water, allows for some very elegant and ingenious behav-iors to have evolved.

There are many species of electric fish that have evolved the ability not onlyto detect electric signals but to produce them as well. Unlike the electric eel,the vast majority of fish are incapable of producing a sufficiently large voltageto use electricity as a weapon. However, even weak electric signals can be usedas a form of communication with a wide and varied vocabulary. One suchspecies uses its electrical signaling ability to attract mates.

Found in the Amazon basin, male Brachyhypopomus pinnicaudatus fish can befound at night making a very odd buzzing noise. This sound is reminiscent ofthe hum of an electricity pylon, and for good reason—the buzz is a compli-cated electrical signal that is the electrical equivalent of a songbird’s warble.


The duck-billed platypus, Ornithorhynchusanatinus. [Tom McHugh / PhotoResearchers, Inc.]

It does seem to serve exactly the same purpose as a bird’s song. It is designed toattract females and to maintain a territory clear of other males. In birds, songsare often judged by females according to their complexity, and the electricsong of Brachyhypopomus is no different.

Female Brachyhypopomus are able to detect the electric songs produced bythe males thanks to electrosensors on their body. Armed with the information,they are able to judge the songs and the males who have produced them.Complex songs are difficult to produce, and so only the best, strongest malesare capable of producing them. This is a suitable signal to woo females as wellas to ward off males who might compete for mates. Depending on thecomplexity of the song, these Amazonian fish can invest between 11 and 22 per-cent of their body’s energy in one night’s singing. Those able to put moreenergy into their song are advertising a strong body and tend to be the mostsuccessful males.

Many other fish communicate in a similar way, using electric signals insocial interactions and even to warn of predators. As with any signal, though,it can be hard to keep the messages quiet. Predators have evolved to pick upon the electric signals produced by other animals. By eavesdropping on electri-cal conversations, predators that can detect electric fields can quickly home inon a ready meal.

Sharks have an especially acute electrosense. Not only can they pick up onthe electric signals produced by electric fish for communication, but they caneven sense the faint electric signals emitted by fish that do not communicateelectrically. This allows sharks to hunt even when visibility is poor or theirprey is hidden. Flat fish such as flounders that bury themselves in the sand toescape can be found with remarkable accuracy thanks to a shark’s electrosense.

At the front of a shark’s head there are a number of visible pores that looklike black spots. These are called ampullae of Lorenzi and they are the organswith which sharks detect electric signals. They consist of a jelly-filled cavity,which is open to the water through a pore in the skin. The cavity is filled withhairs that have an electrical charge. The hairs are sensitive enough to detecteven the tiniest difference in electrical charge between the pore and the bottomof the cavity. The difference in charge causes the nerves attached to the hairs totrigger a signal to the brain. Ampullae of Lorenzi are so sensitive that they candetect 5/1,000,000,000ths of a volt in one 0.4 inch (1 cm) long ampulla.As the weak electric charges given off by other fish is very weak, sharks canonly detect them over quite short distances. Nonetheless, this electrosense isa deadly addition to the shark’s already impressive arsenal of adaptations forhunting.

Perhaps the strangest adaptation for detecting electrical signals, though, isfound in the duck-billed platypus (Ornithorhynchus anatinus). The duck-billed platypus is a very peculiar creature indeed. It’s bill gives it the look of abird. It lays eggs like a reptile. Yet it shows many characteristics of a mam-mal. It is covered in fur, it suckles its young, and it can regulate its own


body temperature. It is such an odd collection of body parts that the firstBritish scientists to see a specimen brought over from Australia thought itwas a hoax, cunningly constructed by a taxidermist. In fact, the duck-billedplatypus is a monotreme mammal, a mammal that lays eggs, and is related tospiny anteaters and, more distantly, marsupials.

It is the unusual bill of the platypus that is capable of detecting electrical sig-nals. The bill itself is very different from a duck’s beak. It is, in fact, a fleshyprotuberance that sits above the mouth. As with sharks, the bill is covered withpores that open out into the water. These pores are surrounded, within the bill,by a ring of electrosensory cells, each attached to a bundle of nerves. Over thebill there are some 40,000 of these electrosensors. The pores have evolvedfrom mucus-producing cells, the membrane of which is sensitive to changesin electrical current. Nerve endings are attached to this membrane and carrysignals to the brain. Each pore is less sensitive than a shark’s ampulla, but thereare many more of them, allowing the platypus to build up a complete picture ofthe electrical environment.

The electrosensors on the platypus’s bill work in partnership with a similarnumber of mechano-sensors that are sensitive to touch. By waving its headabout as it swims, the platypus is able to build up a three-dimensional pictureof where its prey is hiding. It can therefore home in with pinpoint accuracyon its chosen meal, using its flat bill to dig out animals that are hiding withinthe rocks. Its hunting organ may look odd, but it is certainly effective, allowingit to fulfill a unique niche in the murky waters in which it lives.


The electrosensory abilities of sharks can often be thrown off by the pres-ence of metallic, man-made objects in the water, which produce an electricfield. This is perhaps why sharks have been known to attack boats. Thishappens not out of malice, but through confusion over an object which, evolu-tionarily speaking, has arrived in the shark’s world only very recently. This,however, has been a source of inspiration to engineers who are using sharksas a model for robots who can detect, locate, and swim toward electrical signalsgiven off by metallic objects. They are still a way off in replicating the three-dimensional electrical awareness of sharks, but the aim is to produce aquaticrobots that could be used in wreck retrieval or for defense.

FIRE AND SMOKE DETECTORS

Throughout nature there have evolved a number of fascinating creaturesthat have adopted seemingly counterintuitive ways of life. It is hard to believethat any animal would actively seek out the highly dangerous environment ofa burning forest, and yet this is exactly what the aptly named fire beetle does.When everything else is fleeing the inferno, these beetles make a beeline


straight for it, traveling from milesaround. (The black fire beetle also goesunder the name ‘‘jewel beetle’’ thanksto its shiny, iridescent body. They arealso known as buprestid beetles.)

So why this curious behavior? Theanswer lies in the fire beetle’s parentalduties. Its offspring, like many otherinsects, eat wood. To get ahead of thegame adult fire beetles choose recentlyburned and cooled wood that will havebeen cleared of any other insect offspringthat may otherwise compete with the firebeetle larvae for food or attack themdirectly. It has also been suggested thatany chemical defenses that trees produceto prevent attack from insects will have

been neutralized by the fire. What’s more, when the adults arrive they find anempty, predator-free environment in which to attract a partner, mate, and layeggs—activities that are potentially very dangerous with predators nearby.

Fire is quite rare in nature, and so when it happens the fire beetles need toreact quickly. To do so, they are equipped with two extremely sensitive fireand smoke detectors. The first detector is located on the thorax (chest). Underthe pair of middle legs on the fire beetle lie a pair of organs that are very sensi-tive to infrared, the radiation given out by the extreme heat of fire. Whenflying, the beetles hold their middle legs high in the air to expose these infraredsensors. With these sensors, the beetles can detect fire from great distances,even up to 30 miles (50 km) away, so far away that we wouldn’t be able todetect any discernible increase in temperature.

The infrared sensors are backed up by a second set of finely tuned organs.Insect antennae are known to be very sensitive to touch and taste, and the firebeetle’s are no different. Sensors on the beetles’ antennae are able to detectsmoke thanks to very highly sensitive chemoreceptors tuned to sense thechemicals given off by smoking wood. Not only can these antennae detectsmoke per se, but they can even detect the smoke of their favorite pine trees.

Research over the last five years has revealed that the fire sensors use a com-pletely different method for detecting infrared than had been used by humanengineers. Insects, like all animals, are covered with tiny receptors that triggernerves when they move. This is essentially how we feel a breeze blowing overour skin or the touch of an object. Within the fire beetle’s infrared sensor thereare 60 to 70 modified receptors that are each encased by a bubble of the insect’scuticle, the ‘‘skin’’ of the insect. This bubble absorbs infrared radiation atexactly the right wavelength to coincide with the radiation emitted by a forestfire. So when there is a fire, the bubble absorbs the radiation, warms up,


A scanning electron micrograph of thebubble-shaped fire-detector cells of theBuprestid fire beetle. [Volker Steger / PhotoResearchers, Inc.]

expands, and stimulates the receptor inside. By having a sensor on either sideof the body, helped by its two antennae, the fire beetle can locate the fire bydetermining which side of its body is sensing more infrared radiation andhome in on the source.

The infrared sensor in fire beetles is unique in insects. In fact, the sense isonly found in two other groups of animal—the boid snakes and the pit vipersnakes. Again, it is a one-off adaptation that has evolved and which enablesan organism to exploit a unique niche in nature. The value of being able tohome in on a newly created resource gives fire beetles a great competitiveadvantage over similar insects.


Scientists researching the infrared sensors of fire beetles have developed alow-cost prototype sensor that could be used to help detect forest fires. Thesensor is highly sensitive and can automatically monitor large areas of forestand give early fire warnings. Outside of fire-fighting circles, the U.S. Depart-ment of Defense is keeping a close eye on this developing research. There ishuge military potential for a new generation of supersensitive, miniature,robust, infrared detectors for missiles inspired by the small, heat-seeking bee-tle. Current infrared sensors need to be cooled to freezing temperatures beforethey work, which is expensive. The fire-beetle research is leading toward a sol-ution that involves no cooling at all.

INFRARED VISION

Most animals are highly dependent ontheir eyes for sensing the world aroundthem. Many animals see the world as wedo. That is, their eyes are attuned to thesame frequencies of light as humans.Some animals can see a broader frequencyof light, though, and many insects candetect ultraviolet (UV) radiation, whichis invisible to humans. This ability isshown most strikingly when bland-looking flowers are lit with UV light andpicked up with special cameras. Whatmay have looked like a plain white flowerbefore now comes alive with patterns that glow in UV, often directing insectsthat can see these markings to the nectar within the flower.

At the other end of the visible spectrum lies infrared radiation. When anyobject is warmed (either from internal or external sources) it will give offthermal radiation. This emitted radiation is made up of a range of


The head of the western rattlesnake,Crotalus viridis, showing the infrared sens-ing pit below the eye. [Larry Miller / PhotoResearchers, Inc.]

frequencies from the electromagnetic spectrum, but infrared radiation makesup a significant part of it. Perhaps surprisingly, very few animals can detectinfrared radiation. All animals give off heat (typically warmblooded animals,but cold-blooded animals too) and to be able to detect that heat signaturewould give a predator a huge advantage. No amount of clever camouflagewould hide you from a hunter with that ability. One group of insects, thebuprestids, or fire beetles, can detect infrared radiation, but not to any greatresolution. They can detect where there is a fire, but they cannot see discreteshapes in infrared. In fact, there are only two groups of animals that can seeinfrared with any degree of clarity, and they are both snakes. They are thepit vipers, which include rattlesnakes, and the boids, which include boaconstrictors.

These snakes have the unique ability to see infrared thanks to an organ notfound on any other animal—the pit organ. In a pit viper like the rattlesnakethe pit organs are found beneath the eyes and just above the mouth. They aresimply two small holes in the snake’s head and can easily be mistaken for nos-trils. The pit organ is a very sensitive piece of equipment. It is very similar instructure to vertebrate eyes, as it is made up of layers of modified skin cellsstretched out as a membrane above layers of sensitive nerve endings. Thereare two important layers in this membrane. The lower layer holds 2,000 orso receptors that are sensitive to infrared radiation. These are attached tonerves that send the image falling on the membrane to the brain. The top layerof the membrane helps protect the sensitive cells, in effect acting like an infra-red pair of sunglasses. Without it, the sensitive layer would be dazzled by toomuch infrared radiation falling on it. Instead, this protective layer blocks cer-tain frequencies of radiation and only lets other frequencies pass through.The frequencies that pass through correspond exactly to the frequencies ofradiation given off by warm bodies, allowing pit vipers and boids to see theheat given off by its prey.

Like the lens of an eye, the pit itself helps focus infrared light on the sensi-tive membrane within it. To form a clear image on the membrane, however,the pits would have to be very small. This would not let enough infrared radi-ation through, so the pit viper or boid has to put up with a blurry image fallingon the sensitive membrane. Rather than seeing the world of infrared out offocus, though, pit vipers and boids have rather a neat trick to correct the prob-lem. The brain of the snake can correct the image and bring it sharply intofocus. Each of the 2,000 receptors will send, via nerves, a ‘‘message’’ to thebrain when it detects infrared. Each of these receptors interact, however,depending on the image the snake is looking at. By interpreting these interac-tions, the snake’s brain can make sense of the blurry image it is looking at andturn it into a clear, crisp image. The ability to see in sharp focus is clearly veryimportant. If a pit viper is hunting in the dark and needs to strike a tiny mouselocated more than 3 feet (1 m) away, then there is no margin for error and itneeds a precise picture of where its prey is if it is to eat.


This unique adaptation gives pit vipers and boids tremendous advantages.Thanks to their pit organs they can effectively detect and target prey even atnight and in pitch darkness, such as in animal burrows. They may also be usedto avoid predators and to locate suitable basking spots to more effectivelythermoregulate.


There is great interest in military circles in replicating this infrared detec-tion in snakes. The ability of pit vipers and boids to detect heat with suchclarity is a much more elegant and effective solution than current heat-detecting technologies that must be super-cooled for them to work well.Attention is being paid to identifying the molecules that make up the sensitivemembrane within the pit organ itself.

JACOBSON’S ORGAN OF SMELL

The sense of taste and smell is theability to detect chemicals in solids,liquids, or gases. Mostly, the organs oftaste and smell are the nose and tongue.Each of these organs are covered innerve cells that are sensitive to chemicalsand which send messages to the brainwhen they are triggered. There is a greatdeal of variation between organisms intheir ability to taste or smell, and this ispartly due to the number of chemicalreceptors in the nose and tongue.A dog, for example, has 220 million odorreceptors in its nose, compared with ahuman’s 5 million. But the story doesn’tend there. Vertebrates have anotherorgan for sensing chemicals that is moresensitive and is linked with detecting cer-tain volatile chemicals such as phero-mones given off by other animals.Detecting these odors is important forfinding a mate, avoiding predators, andfinding prey. This sensitive olfactoryorgan is called the vomeronasal organ,or Jacobson’s organ.

The Jacobson’s organ is found in allvertebrates. In many species, like


The temple viper, Tropidolaemus wagleri,showing the forked tongue used in collabo-ration with its Jacobson’s organ of smell(vomeronasal organ) to detect prey. [Greg-ory G. Dimijian / Photo Researchers, Inc.]

humans, the organ is not well developed and is not particularly sensitive topheromones and other volatile odors. It has often been referred to as a ‘‘sixthsense’’ organ that humans do not possess, although that is not strictly correctas humans do have some ability to detect pheromones. In all vertebrates, theorgan forms when an organism is a fetus, although in many species it will notdevelop as the fetus grows, and even degrades in the adult. There are somespecies, though, that do have fully developed Jacobson’s organs. It is particu-larly well developed in lions. Males will yawn deeply to taste the air to detectsex hormones of receptive females. It is snakes and lizards, though, that havethe most fully developed Jacobson’s organ and are very successful because of it.

Snakes are remarkable animals with highly sensitive organs for detectinglight, heat, and odors, making them formidable hunters. Their ability to smellis an important part of how a snake builds up a picture of its environment.A snake’s tongue is a key tool in its sense of taste and smell. It constantly flicksout of its mouth and waves from side to side, picking up subtle chemical cues inthe air. As with humans, however, there are relatively few taste receptors on thesnake’s tongue. Experiments have shown that it is not the tongue itself thatdetects odor; the real work is done by the Jacobson’s organ. As the tongueflicks out, any airborne chemicals are absorbed onto its sticky surface. Whenit retracts back into the mouth the tongue passes over the Jacobson’s organand the chemicals are transferred onto it. The Jacobson’s organ is covered inchemoreceptors, specialist nerve cells that can detect volatile chemicals. Thesenerves pass the information to the brain, which forms a picture of the environ-ment based on the information received.

Snakes can build up such a detailed picture of their environment using theJacobson’s organ that they can hunt by smell alone. Tiger snakes on CanacIsland off the coast of Western Australia hunt the eggs and chicks of theisland’s resident gulls. To get to them, the snakes have to get past the adultswho defend their nests ferociously. The adult gulls will attack the tiger snake,clawing and pecking at its head and eyes, often causing blindness. A blind tigersnake can hunt just as well, though, thanks to its highly attuned sense of smell.But how does it build up such a detailed picture of its surroundings by scentalone?

The first clue is with the snake’s forked tongue. The Jacobson’s organ insnakes has two open pits in the roof of the snake’s mouth. When the tongueis withdrawn it must pass over the two pits. As the snake’s tongue is forked,each fork passes over one of the pits. This is hugely significant for the snake.Because it is divided in this way, the Jacobson’s organ can analyze the chemicalslanding on each pit independently. This in turn means that it analyses thechemicals stuck to each fork of the tongue independently. Detecting subtle dif-ferences in the chemicals on each fork allows the snake to build up a detailedimage of its surroundings. Odor from its prey will be stronger on one fork ofthe tongue than another depending on where it is located relative to the snake.Snakes can detect this difference and home in on their unsuspecting victim.


This is precisely how a blinded tiger snake can, despite its lack of vision, track agull chick.


The chemo-receptors of the Jacobson’s organ are different from thosefound in the nose of mammals. The sensitive nerves lack the tiny hairs foundin nasal olfactory nerves, but instead have tiny folds in their surface calledmicrovilli. The nerve cells in the Jacobson’s organ are also made up of a differ-ent group of proteins than found in nasal nerve cells. Despite a good under-standing of the structure of the Jacobson’s organ and the genes that code forthe sensitive nerve cells within it, human engineers have not yet been able tomake use of this knowledge to their own end.

There is a clear goal, though, to use the knowledge to build robotic smellingmachines. On a domestic and commercial scale they could be an important toolfor detecting food that is dangerous for human consumption. Powerful tools fordetecting chemicals do exist, but these are cumbersome devices restricted to thelaboratories of chemists. More portable devices are being developed, but theseinvolve a material such as quartz or silicon that are chemically designed to absorba certain chemical and trigger a sensor. The drawback of these devices is that theyare specific to one particular chemical rather than the range of chemicals that canbe detected by the Jacobson’s organ. When it comes to useful and adaptablechemical detectors, human engineers have a long way to go to better those foundin a small organ in the mouth of a snakes and lizards.

ODOROUS GENES—THE MAJOR HISTOCOMPATIBILITY COMPLEX

Despite the stigma attached to it, body odor plays an important role in socialand sexual activities in many social species. Although we often do our best tocover up our own odor, it can even influence human behavior. In particular,there is one set of genes in humans and other animals that has an intriguingrole in determining an individual’s unique odor. Over time, animals likehumans have evolved to be able to detect and respond to these unique odors.What this means is that humans, in effect, have the ability to smell each others’genes—an ability that has led to the further evolution of a fascinating set ofbehaviors.

The group of genes that is important in body odor is a group of some 150genes called the Major Histocompatibility Complex, or MHC for short. Theirprimary function is to code for proteins that are necessary for a fully function-ing immune system. These proteins are responsible for recognizing whethersomething is part of the body or whether it is a foreign pathogen that mustbe killed before it can cause disease. There is a second function of the MHCgenes, however, and that is to produce body odor. It is unclear exactly why thisis the case.


With any gene, there are different types of that gene, called alleles, that anindividual can possess. Different alleles for the genes that make up our bloodcells give rise to the different blood types that we have (A, B, AB, or O). Thegenes of the MHC are no different, but the MHC genes have many (50 to over100) different alleles that can be picked from to make up the 150 or so genesthat make up the MHC gene complex. With so many possible combinations,this leads to a great deal of variation between individuals. There is so muchvariation that we can think of each human being as having a unique MHC genecomplex. This, in turn, means that we each have a unique smell.

Having a unique odor may not seem that significant, but the link betweengenes and a detectable odor is an important one. If you can recognize a par-ticular body odor, you can detect a particular set of genes, or rather the specificalleles that make up the MHC gene complex. Humans can smell genes! Thisrecognition through odor has led to humans evolving a number of importantbehaviors in response to body odor. It allows newborn babies to recognizeparents and other relatives, and it is one of the ways in which we, whether weknow it or not, choose sexual partners.

From an evolutionary point of view, there are certain advantages to recog-nizing the genes that another individual possesses. One of the most importantis for an individual to recognize others that are closely related. Closely relatedindividuals are more likely to share the same combination of alleles (rememberthat genes come in different ‘‘flavors’’ called alleles). It follows that it makessense from an evolutionary point of view to help out close relatives in orderto help them to pass on their genes that you are likely to share.

If an individual’s genes determine their smell, relatives can detect who has asimilar genetic makeup by detecting who has a similar body odor. They maythen have evolved to help out individuals who smell the same. In mice, theMHC body odor is a key mechanism for individuals to detect how closelyrelated they are. This is critical for females to recognize their offspring andto nurse the right young. Given that mice can live together in large groups ofseveral families this is an important behavior as identical-looking young couldeasily get mixed up.

Humans show a similar recognition of kin through smell. Studies whereindividuals are asked to show a preference for the smells on clothing wornby related and non-related infants have shown that fathers can recognizetheir babies by their smell. This is an important skill to possess. Given thatparenting is a huge commitment in time and energy a father needs to be surethat he is giving his care and attention to his own child. With the risk that amale’s partner could have mated with another male it makes sense, from anevolutionary point of view, to be sure that the infant he is caring for is trulyhis own. Of course, infidelity may not be so high in modern society anddetection of relatedness by smell is far from infallible, but even today humanmales behave differently toward the smell of their own child to that of anunrelated one.


Wemight think that human behavior in response to body odor is somethingthat we have, evolutionarily speaking, outgrown. But this is not the case.In choosing sexual partners there are some whom we are very much attractedto and those that we are not. We tend to think that this is purely physical,but beneath all that it comes again down to body odor and its link to our genes.In picking a good mate, this time it is better to pick someone who is not closelyrelated. Inbreeding in humans can result in certain mental and physical defi-ciencies in the resulting offspring. From an evolutionary point of view, then,it is best to avoid relatives in choosing a mate so that your child is fit and ismore likely to pass on your genes in subsequent generations. This is whyfemale humans tend to choose males with an odor representative of a verydissimilar set of MHC genes to their own.

Interestingly, though, females prefer the odor of males with very similarMHC genes to their own (i.e., more closely related) when they are takingbirth control pills. Females on birth control pills show very similar physio-logical signs to being pregnant. Pregnancy is a potentially dangerous timefor both mother and unborn child. Given that relatives are more likely tohelp out an individual it makes sense for a female to seek out and form a closebond with males that are related to her. At this time, a female now prefers theodor of family. These preferences have all been shown by the same set ofstudies whereby individuals are asked to show a preference for the smells onT-shirts that have been worn by related and non-related individuals forseveral days.

In humans, the relationship between body odor and the MHC genesrepresent a fascinating array of adaptations that are about helping out closelyrelated individuals or mating with unrelated individuals. It demonstrates thathumans are still very much a product of evolution and that we still respondto the instincts that have evolved over millions of years.


In humans and other animals there is no particular organ of smell that asevolved specifically to detect MHC-related body odor. Both the nasal andvomeronasal smell receptors are involved. The key for the behaviors discussedabove is how the brain interprets the information received by the nose anddetermines whether it is the smell of a relative or a not. It is this brain activitythat robotics experts are trying to recreate in developing ‘‘electronic noses.’’Progress so far has been to develop sensors that are designed to detect one par-ticular smell (for example, in designing robots used to track down the source ofa particular odor). Traditionally, these electronic noses could only detect onesmell, but there are new ones available today that can distinguish betweenseveral smell compounds. They have been used in the discrimination of a rangeof different odor sources, such as food, biological sources for medical applica-tions, and for environmental applications.


MAGNETIC SENSE

The ability to build up a picture of the surrounding environment is anessential skill to have. Several senses have evolved, and often a number arecombined by an organism to identify what is nearby. Vision, hearing, and smellare the dominant senses, but there are other senses that are employed byorganisms that live more specialist lifestyles where these other senses are of lessuse. One important sense for organisms navigating long distances or under-ground is the ability to detect the earth’s magnetic field.

Several species can detect magnetic fields. Migratory birds use the skill tocover the huge distances from summer breeding grounds to over-winteringsites. Naked mole rats are dependent on detecting the earth’s magnetic fieldto navigate below ground where there are few, if any, cues to keep a sense ofdirection. Even ants employ a magnetic compass to return home after forag-ing. Other animals recorded as having a magnetic sense include bacteria,sharks, honey bees, and homing pigeons. Each of these organisms seems todetect magnetic fields in the same way—by tiny specialized bio-particles calledmagnetosomes.

Magnetosomes are organelles like mitochondria or chloroplasts. They aretiny, organ-like structures that live within cells. Magnetosomes contain evensmaller particles of an iron-containing substance called magnetite. Magnetiteis produced by the organism from iron, oxygen, and water, and it has the high-est electrical conductivity of any solid biological molecule. This is crucialbecause the earth’s magnetic field is very weak—no other material would beaffected by it. In any magnetic field, these magnetite particles line up in thedirection of the field. On a very tiny scale it is like iron filings following themagnetic field of a bar magnet. It is this property of magnetite that organismscan exploit to give them a sense of direction.

In some bacteria, the shifting of the tiny magnetite particles is sufficient tophysically pull the single-celled organism in the direction of the earth’s mag-netic field. In multicellular organisms, though, that is simply just not possible.There must be some mechanism that translates the position of the magnetiteparticles into useful information that is sent to the brain. Magnetosomes,therefore, must be connected to nerves. To trigger the nerve, the magneto-some acts as a switch that can send a signal along the neuron. With many hun-dreds of magnetosomes, organisms can use the information they provide toorient themselves to the plane of the earth’s magnetic field.

There have been several suggestions as to how these magnetic switcheswork, and no one is quite sure which is right. It seems that different types ofswitches have evolved in different species. Migratory birds and homingpigeons simply detect the angle they are moving away from the plane of theearth’s magnetic field. Certain bats, on the other hand, can more directlydetect the earth’s field and can detect which way is north and which way issouth—something that birds are incapable of.


There is no doubt that a magnetic sense of direction is a useful tool. Marineturtles are able to use it to navigate the oceans of the world to return to the verysame beach they hatched at to lay their own eggs—not bad going for an animalthat has to cross thousands of miles to get there in an environment bereft ofany significant directional markers. Similarly, naked mole rats are able to findtheir way over the long distances of their lightless underground tunnels thanksto their extraordinary ability to detect the earth’s magnetic field. The nakedmole rat is the only animal known to constantly check its position in relationto the earth’s field; migratory birds only check their direction in relation tothe magnetic field once a day.

Despite these remarkable feats of navigation, the earth’s magnetic field is nota very reliable thing to detect. It varies in strength and even direction over time.The earth’s poles slightly shift their geographic location every year and haveeven reversed entirely 10 times in the last three million years! Thus, even molerats and marine turtles have to rely on other cues to find their way around.

It was thought that all animals detected magnetic fields using magneto-somes, but recent research has given evidence to suggest that some species ofbird can physically see the lines of the earth’s magnetic field. The ability tosee a magnetic field seems to come from a group of light-sensitive proteinscalled cryptochromes, which have been found in the eyes of some birds.Normally, these molecules are involved with animal and plant body clocks.In plants, they also regulate plant growth. Plants are very responsive tomagnetic fields. Seeds do not germinate in space, yet when they are grown instrong magnetic fields they grow at a much faster rate than under normalconditions. This suggests the link between cryptochromes and magnetism.

Cryptochromes have been detected in the retinal nerves of migratory birds.These nerve cells are active at dusk in certain migratory birds at the time whenexperiments show that they are using the earth’s magnetic field to orient them-selves. There is still some work to be carried out to determine if this theory iscorrect, but it is thought that birds can directly see the lines of the earth’s mag-netic field. This might look just like a ‘‘head-up’’ display seen in some cars andin fighter jets. This would be distracting though if field lines were constantlylaid over a bird’s vision. This may explain why birds only check their orienta-tion against the earth’s field once a day and why, in the birds that have beenstudied so far, the retinal nerves with cryptochromes are only active at duskwhen birds are setting off.


In the 1950s, a patent was registered for a machine that used a strong mag-netic field to enhance plant growth from seeds. More recently, there are agri-cultural companies selling devices that magnetize the water used in irrigationsystems, with the aim of stimulating a strong and fast growth of crops. It isnot clear, though, whether these commercial devices do indeed work.


Perhaps the biggest area of research is in the growth of plants in space. Shouldhumans ever move to colonize space and other planets, the problem of plantsrequiring a magnetic field in which to grow will need to be overcome.

INSECT ANTENNAE

All insects have an excellent sense oftaste and smell. With this sense, insectscan detect whether food is palatable,discern which are the right plants onwhich to lay their eggs, and detectchemical messages sent by other insects.It is perhaps not surprising, then, thatthere are many taste and smell sensorslocated all over an insect’s body. Theycan be found on the tarsal segments ofthe legs (tarsi are like our feet), on themouthparts, and even on the ovipositor,the organ through which eggs are laid.However, insects’ most specializedorgans of taste and smell are the

antennae—the paired organs that sit on top of an insect’s head.Despite their antennae and other sense organs, insects do not have a wide

range of smell so that their relatively small brains do not get overloaded withsmell information. The sense organs are tuned to pick up only scents that areimportant to the insect in question. It is this job in which antennae performparticularly well. They can detect the tiniest trace of an odor that they areprogrammed to detect. Certain male moths can detect the scent of a femalefrom several miles away. Carrion beetles can detect rotting flesh over similardistances.

Insect antennae are adapted to detecting airborne odors. As with all insectsense organs, they have evolved from the basic cuticle that covers the insect’sbody. Antennae can take a wide variety of shapes, from simple bristles to elabo-rate feathered arrangements. All antennae, though, are covered with the basicsensory structure called a sensillum. Each sensillum is only about 1 thousandthof a millimeter (1 micrometer) in diameter, so antennae can be covered inthousands of these tiny structures. The surface of the sensillum is puncturedby tiny pores. Behind each pore is a chamber, called the pore kettle, lined witha membrane, which itself is punctured by even smaller pores. These pores inthe membrane lead, via a microscopic tube, to an electrically chargedmembrane that is linked to a bundle of nerves.

Airborne odor molecules are trapped in the pore kettle and transferred viathe micro-tubes to the electrically charged membrane. The odor moleculeswill interact with the charged membrane, causing it to lose its electric charge.


A scanning electron micrograph of a moth’santenna showing the fine, branching hairs thatare covered with sensilla. [Edward Kinsman /Photo Researchers, Inc.]

This, in turn, stimulates a nerve impulse that leads to the brain, where theinformation is interpreted and the odor identified. Exactly how the odormolecules interact with the electrically charged membrane allows the insectto determine the specific scent. In this way, insects can distinguish the scentfrom a sexually receptive female and the scent from a nectar-rich flower.

Many insect species have evolved specialized antennae for specific purposes.Perhaps the most striking are the feathered antennae of male moths.By detecting the scent of a receptive female as early as possible, a male with akeen sense of smell can find his way to her before any other male, giving himan important advantage over his competitors. The feathered antennae of malesilk moth (Bombyx mori) have evolved for just this reason. The antennae havemany different branches with which to maximize the chance of picking up thefaint odor of the female pheromone. Each feathered antennae has about17,000 sensilla, each of which is covered in some 3,000 pores. With a total of102 million hormone-detecting pores, we can see how the male silk moth hassuch a sensitive sense of smell. Only 100 pheromone molecules are needed forthe moth to detect the odor, allowing them to detect a female from miles away.

Insects’ sensitivity to pheromone odors has allowed several key behaviors toevolve. In addition to communicating during mating, insects such as fruit fliescan use the hormone to control their swarming behavior, which is an effectivedefense against predation. Pheromones may also be used to warn of a predatorapproaching, allowing other individuals to take evasive maneuvers or mount adefense. This is especially important in social insects like ants, wasps, and beesthat can smell if an unwanted visitor has invaded their nest. However, it is notjust smell that antennae are used for. They are also used by insects to feel theirway around their environment, as a flight-control mechanism and even as abody clock.

The touch sense is particularly well adapted in grasshoppers and crickets(Orthoptera). Their antennae are typically long and thin and hinged at thehead to allow them to feel the environment around them. The longest anten-nae are found in the bush-crickets (otherwise called katydids), which haveantennae some three times the length of their body. Sensilla are used for touchas well as smell. When they are deformed, they trigger a nerve impulse that isinterpreted by the brain as some form of contact. Again, the high density ofsensilla gives a remarkable sense of touch. Some grasshoppers are able todetect air flowing past them at only one-tenth of a mile per hour.

Some species have taken the role of the antenna in touch and taste even fur-ther. Like many wasps, beewolf wasps (Philanthus triangulum) use their anten-nae to check up on their developing brood. In addition to building up apicture of the welfare of their offspring, beewolf wasps are doing somethingelse with their antennae at the same time. It seems that their antennae secretean antibiotic with which they cover their brood, protecting it from bacteriaand fungal attack. Beewolf antennae have special reservoirs in them in whichthey nourish and cultivate a particular species of bacteria called Streptomyces.


This bacteria is not harmful to the adult wasp or its offspring; far from it.Streptomyces naturally produces and excretes an antibiotic, which is what thewasp makes excellent use of to sterilize its nest. The glands in the antennaeprovide a safe place for the bacteria to flourish, and they even produce thenutrients needed by the bacteria to grow—a perfect symbiosis between bacte-rium and wasp.

Finally, in addition to acting as sensory organs, antennae have a mechanicalrole in flight. The fastest and most acrobatic insect fliers are the two-wingedflies. The key to their success are the vestigial second pair of wings, called hal-teres, that have evolved into a gyroscope-like organ to give balance when mak-ing sharp turns (see Insect Flight). Insects that have retained both pairs ofwings for flapping flight do not have these halteres for balancing. Instead, theyuse their antennae to the same effect. Sensors at the base of the antenna candetect any pull on the antenna that might come about by a sudden turn or agust of wind pushing an insect off course. The brain receives a signalfrom these sensors and can effect a correction in the flight path. These antennasensors are particularly important to insects that fly in poor light, such asmoths that are active at dusk. Experiments have shown that removing thesesensors leads the moths to fly erratically, resulting in crashes. It seems thatthe antenna are critical for ensuring that the moth can keep a constant and evenbearing.


Insect antennae have proven to offer quite a treasure trove of ideas forhuman application. For example, the beewolf’s antenna-based medicinecabinet is offering a potential new antibiotic for use in medicine. Insects thatcan detect decaying fruit are being used to develop sensitive devices that candetect the early signs of fruit and vegetable decay. Some scientist are evenusing the insects themselves by attaching fine electrodes into the antennaeand measuring the response to decay odor molecules.

By understanding exactly how insects smell, scientists are looking to developmore effective insect repellents. In fruit flies, there is one particular sensorthat controls smell. Scientists are currently testing whether the same sensor isused by mosquitoes to smell. If it is, the task is to develop a repellent thatblocks this particular sensor. This would disable a mosquito’s ability to sniffout humans, a crucial step in tackling malaria and other mosquito-bornediseases.

SPECIALIZED EYES

Throughout the animal kingdom, eyes have evolved into highly special-ized organs capable of absorbing enormous amounts of data about the envi-ronment and feeding it to the brain. Here, the information is converted into


a picture that the animal sees. With thisinformation, the animal can navigate itsenvironment, moving away from dangerand toward food and mates. In somespecies, though, the eyes have evolvedin a curious way—to actually reducetheir visual acuity. Given that a senseof vision is so important to so manyspecies, why would some species evolvein a way as to seemingly impair theireyesight?

If you were able to look through theeyes of a dragonfly larva things wouldbe a bit of a blur, or to be more preciseeverything would be seen with double-vision. Walk around with your eyescrossed for a while and you wouldquickly become disoriented. Yet this is precisely how a dragonfly larva seesthe world for most of the time. Adult dragonflies skim about, with great agility,above water and land hunting for small insects to eat. Their larvae, however,are bound to an aquatic life. They live underwater feeding off other under-water insects, worms, crustaceans, and even quick-moving small fish.

Dragonfly larvae look very much like an alien predator, and they areindeed voracious, but how can they devour so much food with such bad eye-sight? They key is in how the dragonfly larva hunts its prey. Rather thanstalking it or using a quick body speed, the young dragonfly will sit and waituntil its food comes to it. Well camouflaged, the dragonfly larva can strikewith lightening speed—anything that strays too close will not stand a chance.It does this thanks to its crossed-eyes. Rather than being randomly poor-sighted, the dragonfly’s eyes are focussed on a particular point a fixed dis-tance away from its head (the distance varies between species). This distanceis exactly the range of its formidable jaw, which can strike and spear preybefore it can react. Thus, when a passing animal comes sharply into focus,the dragonfly larva knows to deploy its weapon, guaranteeing a successfulstrike. You can mimic the visual effect the dragonfly employs. Cross youreyes by focussing on a point a few inches from your nose and move yourfinger from arms length toward your face. You will see two copies of yourfinger when it is far away, but when it reaches the point your eyes arefocussed on you will see just your one finger. It is at this point the dragonflywould strike.

The dragonfly larva’s jaw, called a ‘‘mask’’ because of the way it sits over theindividual’s face before a strike, is a highly modified, hinged organ that canextend rapidly toward a prey animal and impale it on the spike with which itis tipped. Once skewered, the prey is drawn back to the larva where its regular


A dragonfly larva poised to strike at a mosquitolarva with its modified jaw. The range of its jawcoincides exactly with the distance at which thedragonfly larva’s eye focus on an object, makingits vision an effective targeting device. [RobertNoonan / Photo Researchers, Inc.]

jaws can chew on the meal. The complete action from striking to drawing themask back to its starting position takes 25 thousandths of a second (0.025 sec-onds). The lightening-fast strike is achieved by the powerful abdomen musclescontracting and sending a rush of blood shooting into the mask. The mask isretracted by direct muscular control.

The dragonfly larva has evolved a particular field of vision allowing it tohunt in a highly specialized way. The same is true of the Portia spider, whichsacrifices some of its visual acuity to enhance its ability to hunt in a veryintelligent way. Small animals like spiders are rarely known for their thinkingability, but the jumping spider, Portia, shows up not only other spiders, buteven large mammals when it comes to problem solving. Portia spiders havea curious hunting strategy. They hunt other spiders, strolling right into theirlair to make a kill. For a spider that is less than 0.3 inches (1 cm) longand slightly built, that is a bold strategy to adopt. The Portia spider doesnot rely on brute strength when it hunts, however. Instead it relies on itsbrain.

These spiders are devious hunters. Rarely will they head for a full frontalassault on their prey. Instead they will find a way of sneaking around them tomake the killing blow from behind or above, where they won’t be noticed. Thisis easier said than done. Predators the size of Portia do not have large brains,which means that hunting strategies are typically based on finding prey, fixingit in a line of sight, and charging straight in. If the prey disappears from view,this normally results in the hunter losing interest. Portia spiders are different.Having excellent eyesight, even sharper than the vision of some mammals, ithas no problem in spotting its prey. Having found prey, though, Portia spidersstay put. Instead of rushing toward their prey, they begin to scan the environ-ment with their keen eyes. They are working out a path that will get them,unnoticed, to a place where they can strike.

In itself, working out a suitable path is a remarkable piece of problem solv-ing. What is even more impressive is that it can remember this path and followit even if it loses sight of its prey. So precise is this behavior that once they haveworked out the correct path they will follow it even if there are alternativeroutes that, on the face of it, seem preferable. Almost inevitably, the huntingPortia spider will find its way to the ideal place from which to launch its attack,and it will make the kill.

Given that Portia spiders have no more brain cells than their tiny size allows(they have more than a housefly, but fewer than a honeybee), it seems impos-sible that they can solve such complex problems. The answer seems to be intheir eyes. Although they produce a very sharp image, Portia spider eyes, likethe rest of the body, are very small. This means they can only look at one pointin space at a time—it is a little like constantly peering through a keyhole. Thismeans that to work out its path to its prey, a Portia spider must look methodi-cally at each point along the various paths, slowly building up a picture of theenvironment frame by frame.


The way Portia spiders view the world is hugely important to their ability tosolve problems. Their way of seeing is very different from how animals likehumans build up a picture of the world. We see everything in our wide fieldof vision all at once. We are not really interested in all the information wegather, however, and instead we tend to focus on one thing. It is up to ourbrain to filter out all the useless information that our eyes gather, which con-sumes a lot of brain power. Smaller animals with smaller brains simply donot have the mental capacity to filter out useless information collected by theirsenses and solve complex problems as well. This is why smaller animals tendnot to be able to know they are moving toward food unless they can directlysense it. Portia spiders, however, are different. They do not need to waste brainpower filtering out the useless information because they are only focusing theireyes on what is important. This saves brain power for making the remarkabledeductions they make in choosing and following the right path to their prey.


The problem-solving abilities of Portia spiders are being studied by artificialintelligence programmers who are trying to develop problem-solving algo-rithms for computers and robots. The view is that with a comparatively smallbrain, the processes by which the spider solves the challenges in front of itcould easily be replicated in artificial systems that currently are incapable ofcreating innovative solutions when faced with a problem. That is the goal,but unfortunately the secrets of how the jumping spider’s brain works are stillvery much locked away in its tiny head. There is no doubt, though, this such arelatively simple brain is an excellent model for such studies.

MANTIS SHRIMP EYES

Mantis shrimp are neither mantids orshrimp, yet they come by their namethanks to their resemblance to both.Rather, they are an order of large inverte-brates that live on the ocean floor in thetropics of the Pacific and Indian Oceans.They are often vibrantly colored but arewell armored, thanks to a tough carapaceand a hard, shield-like covering over theirabdomen called the telson. Their secondpair of limbs are large and, at rest, arefolded up close to their body. These limbsare fearsome weapons that the mantisshrimp uses for hunting. In some species,these limbs have evolved into a sharpspear for impaling fish. In others, the


The mantis shrimp, Odontodactylus sp., haseyes that contain up to 16 different lightreceptor cells (depending on species), com-pared with the four light receptor cells inhumans. [Georgette Douwma / PhotoResearchers, Inc.]

limbs are enlarged into a heavy club-like structure. Either way, when prey isnearby, the limbs can flick out in around 4milliseconds and with the same forceas a .22 caliber bullet being fired from a gun. These creatures have been knownto shatter the glass walls of aquaria in which they have been held captive.

There is no doubt that mantis shrimp have the tools of a hunter. What’smore, they have the eyesight to stalk prey from a distance and then to landthe knock-out blow. It is acknowledged that mantis shrimp have the most com-plex eyes in the animal kingdom—a fact that gives potential prey little chanceof escaping unnoticed.

Mantis shrimp eyes are, relatively, very large. Scaling the animal up to thesize of a human would mean eyes the size of soccer balls. Both eyes aremounted on highly mobile stalks, which are capable of moving independentlyof each other. These stalks have a much greater range of movement than isfound in similar structures in other animals, thanks to their eight controllingmuscles. This gives the mantis shrimp a great deal of flexibility over how itinspects its immediate surroundings. It can look at one object in detail usingboth eyes, giving more depth perception. Alternatively, it can cast its eyesabout independently and look at different objects with each eye, giving lessspecific detail but a great field of vision.

The eye itself is similar to the eye of an insect—it is a compound eye made upof around 10,000 individual ommatidia (simple eyes each with its own lens).Insects’ eyes are simply made up of a cluster of such ommatidia, but the mantisshrimp eye is a little more complex. Each eye is made up of two flattened hemi-spheres that are divided by six parallel rows of highly specialized ommatidia, col-lectively known as the midband. The eye is therefore split into three regions—each hemisphere and the specialized midband. This means that each eye can lookat an object with three different parts of the same eye, each having a subtly differ-ent view of the object. Humans have two eyes that work together to produce bin-ocular vision, allowing us to perceive depth and distance. Each eye of the mantisshrimp has trinocular vision, giving even greater spatial awareness of a particularobject by triangulation. Both eyes used together can give even greater spatialawareness, allowing for a deadly accurate strike with their limbs.

Each of the two hemispheres are used for detecting motion, like insect eyes,and shapes. To do this, they contain a single type of simple light receptor. It isin the midband where the mantis shrimp eye can detect such complex environ-mental information.

Rows one to four of the midband are involved with detecting color. Mantisshrimp are able to see a much wider range of colors than humans, ranging frominfrared to ultraviolet (UV). The vertebrate eye has four types of visualreceptors—one type of ‘‘rod’’ receptor that is very sensitive to light and threetypes of ‘‘cone’’ receptors for detecting red, green, and blue light. The mantisshrimp can see so many more colors because it has up to 12 color receptorsinstead of just three. Up to four of these are adapted to detect UV light. Thelight receptors are layered in the ommatidium, one on top of the other.


Each layer is specialized for detecting a certain wavelength of light. These12 color receptors allow mantis shrimps to discern 10 times the colors wecan—some 100,000.

Rows five and six of the midband have a further class of light receptor. Thesereceptors are specialized for detecting up to four planes of polarized light. Thisis not easy to visualize. As the name suggests, three-dimensional objects havethree dimensions, or planes—vertical, horizontal, and diagonal. Light can beapproximated in the same way. It can be split into different planes, althoughthere are many more than three. When applied through certain filters, onlylight in a certain plane can get through. This is what Polaroid sunglasses do;they filter everything but one plane of light. So to see what a mantis shrimp seesyou will need four pairs of sunglasses! Water acts as a filter of light, so beingable to detect different planes of light gives a tremendous advantage.

By being able to see planes of polarized light, mantis shrimps get much bettercontrast on images and can spot creatures that might otherwise be invisiblebecause of how their bodies reflect light under water. In short, a polarized lightreceptor enables themantis shrimp to spot prey among the tricky light conditionsof the ocean floor. What’s more, as the phases of the moon each produce light indifferent planes, mantis shrimp can ‘‘see’’ these phases, giving them an effectivemonthly calendar—very handy for predicting tides that can be potentially dan-gerous for creatures on the sea bed—and very handy for knowing when femalesare ready to mate as they are only fertile at certain phases of the tidal cycle.

The midband gives the mantis shrimp a huge scope of visual acuity, yet itonly covers about 2–3 percent of the visual field at any one time. With suchmobile eye-stalks, though, the mantis shrimp has little trouble scanning its sur-roundings with this highly specialized part of the eye. The complex eye andvision of mantis shrimps has led to the evolution of a number of elaboratebehaviors. Given such powerful weapons at their disposal, fighting with fellowmantis shrimps over territory is potentially a dangerous affair. To avoid mis-hap and injury, they have evolved a series of highly complex, ritualized fight-ing. Signals are given during these fights by visual cues, changing color andeven fluorescing. Individuals have a good memory and can recognize closeneighbors well. Thanks to their eyesight, many signals can be given out toallow mantis shrimp to interact with a wide range of complex social behaviors.


Only recently was it discovered that at least one species of mantis shrimp iscapable of seeing circular polarized light, a plane of light that spirals clockwiseor counterclockwise rather than being in a ‘‘straight line,’’ Scientists have beenaware of this plane of light for many years and indeed have created devices thatfilter and detect it. Humans use circular polarized light filers in photography,medical photography, and in detecting objects in turbid environments. It ishoped that new insights from the mantis shrimp’s vision may help developnew ways of detecting this unique plane of light for a variety of purposes.


7

COMMUNICATION

COMMUNICATION—HUMAN INVENTION

Sharing information is perhaps the most important human trait that has shapedour evolution and colonization of the planet. However, it is by no meansuniquely human to share information. It is fair to say that probably all organismsshare information to some extent or the other, but our species in particular hasdeveloped a huge array of tools with which to disseminate knowledge.

Writing appeared in human history at around 3500 BC with the Phoenicians,who developed the first alphabet, and the Sumerians, who developed a picto-gram form of writing to represent events. At around the same time, the Egyp-tians developed their pictogram-based writing called hieroglyphics.It wasn’t until around 1775 BC in Greece, though, when the first phoneticalphabet was produced that could accurately replicate the spoken languageand which was therefore limitless in the words it could represent.

It is unclear what these early forms of writing would have been used for.Evidence that has persisted through the years shows that, principally, writingwas used to record events and to tell stories. We know, though, that the firstencyclopedia was written in Syria in 1270 BC, which allowed literate scholarsto increase their knowledge from a book rather than from a series of tutors.Although few could read, this was a significant step forward because no longerwas the transfer of knowledge restricted to word of mouth. It wasn’t until530 BC, though, that the first library was established in Greece, which held sev-eral key texts together in one place.

The physical transfer of data from place to place probably originated inChina. The first record of a postal service dates back to 900 BC. Previously,news would have spread through traveling individuals, again only by word of

mouth. A postal service allowed a wide range of information to be passed overgreat distances, although again only between the rich and the educated. Theidea of a postal service was taken further by the Greeks 200 years later withthe first use of homing pigeons to send messages. This form of communicationwas used right up until the early twentieth century.

Writing was still the key form of transmitted communication from 200 BC to100 AD when the Romans dominated Europe. Messages were carried by humanmessengers, albeit carried on horseback. Around this time, though, fire sta-tions—signal fires located on high ground—were used to carry signals quicklyacross great distances. However, these were very limited in the range of infor-mation that could be transmitted.

Despite these advances, which allowed the sharing of ideas and messagesamong the educated and royal classes, there was still little innovation in sharinginformation to the masses. The first printing press was invented in 305 in China,althoughmoveable type was not to be invented, again in China, until 1049.Withthe increase in numbers of people who could read, newspapers became popularin Europe from 1450, which coincided with the European invention of themoveable type printing press, some 400 years after the Chinese invention!

Until the eighteenth century, human innovation for sharing informationwas restricted to the invention of writing and of methods for reproducing itreadily (printing presses) and of disseminating it widely (in books and newspa-pers). This changed in 1793 with the invention of the long distance semaphoretelegraph line. Semaphore using flags was invented around 100 years earlierand was put to use mainly in naval combat to send messages from ship to ship.Long-distance semaphore worked on the same principle, but with large towersto relay messages rather than people with flags.

Forty years after the invention of the long-distance semaphore telegraph,the first long-distance electric telegraph was invented. Pulses of electricityrunning down the line could be used to carry messages quickly and over longdistances. The language used to exploit this was Morse code, named afterSamuel Morse who invented it. With these tapped sequences of dots anddashes representing letters of words, entire messages could be shared betweenwhatever places were connected with a physical line. In 1858, the first transat-lantic cable was laid that connected Britain to America and allowed messagesto fly back and forth between the two.

From the turn of the twentieth century, Morse code messages could be senteven without cables, thanks to the use of radio waves. The so-called wirelesstelegraphy therefore allowed messages to be sent between any two emittersand receivers of radio waves. By this time, Alexander Graham Bell had alreadyinvented the telephone and humans were already well on the way to sharinginformation by spoken word again, but this time remotely over long distances.

The microphone had already been invented in the mid-1800s, and so theonly challenge was how to send the data it could capture. Various bandwidthsof the electromagnetic spectrum were used, as they are today, to carry words


through the air. For permanent records, magnetic tape had been developed tostore spoken data captured by microphones. The next big step was, of course,the development of moving pictures in the early 1900s. Television was to fol-low in 1923, receiving signals through an antenna and transmitting themthrough speakers and onto a screen via a cathode ray tube. The cathode raytube works by an emitter that fires charged particles (ions) onto a sensitivescreen to create an image. Electromagnets in the tube direct the ions accordingto the signal received to produce the desired picture. With humans developingthe ability to send satellites into orbit around the earth, television signals couldbe sent anywhere on the planet.

Alongside the development of television and radio media, telephones werestill being used to directly connect individuals over huge distances. From the1970s, telephone users were no longer restricted to being physically connectedto the telephone exchange. The use of satellites and fixed radio receiversallowed a cellular telephone network to be established, potentially connectingpeople wherever they are on the planet.

From the mid-twentieth century, television and radio were principallyresponsible for the widespread dissemination of information across the world.As the technology improved and costs were reduced, this information wasincreasingly available. From the 1950s, there was another leap forward intransferring information with the first commercial sale of home computers.The invention of computers represented an interesting problem for theirhuman engineers. They held great potential for solving problems beyondhuman capability, but how was this potential to be unlocked? Computerdesigners had to develop a language that both humans and computers couldunderstand. Many computer languages have evolved, but all lack the flexibilityand range of expression available in the various human languages that haveevolved in nature. It is a goal of computer programmers to design computersthan can understand human languages, but we are still some way off inachieving it.

The rise of the personal computer paved the way for the evolution of theInternet, which began in 1969 with ARPAnet, a network that was used totransfer information between military bases in the United States. This evolvedthrough a number of guises until the release of the world wide web in 1994,which has led to an enormous amount of information being stored and sharedacross the world. The only limitation now seems to be in adding the collectiveknowledge of human experience to the platform. Potentially, every humanbeing with access to the Internet has access to the entire sphere of humanknowledge.

HUMAN BRAIN

The human brain is the computer of the body. Made from around 100 billionnerve cells, it is the communications hub that controls nearly every function in

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the human body. The brain controls our senses, our movement, and our memo-ries. From this one organ all the processes that keep us alive are regulated so ourbodies keep operating under optimal conditions. It is perhaps small wonder,then, that an organ that represents only 5 percent of our body mass uses up over20 percent of the energy our body burns to stay alive. This is why there is onesupport cell (called a glial cell) for every two nerve cells in our brain to deliverenergy directly to our brain cells throughout the day.

Despite being made up of a single building block, nerve cells, the brain is di-vided into several regions, each of which is responsible for a different function.Perhaps one of the most fundamental of these is the sensory cortex. This partof the brain receives information collected by our sense organs and interpretsit to build up a mental picture of the environment around us. What’s more, itcan take this vast amount of data and determine, in the tiniest fraction of asecond, what information is relevant and what is not. We can therefore pin-point a miniscule object in our broad field of vision or concentrate on thesound of someone speaking against the cacophony of a busy street.

Our brain even has the capacity to interpret more data than we can normallyreceive from our sense organs. Some humans have ‘‘super-senses’’ in that theyhave sense organs that can detect a greater range of colors, sounds, or tastesthan the average human. The brain has no problem in interpreting this extra


The human brain showing the various areas that control different functions. [Medi-Visuals / Photo Researchers, Inc.]

information that comes to it from the super sense organ. The limit is to theinformation coming in, not to the organ that processes it.

Although the sensory cortex is the main part of the brain for dealing withthe senses, a different area, called the PEG region, is responsible forhand-eye coordination. Perhaps not surprisingly the PEG region in the pari-etal cortex is much more active in top athletes than in the average person. Thispart of the brain contains a map of the space around us and an internal map ofour bodies. It works by coordinating the two maps so we can put our bodiesexactly where we want them. This part of the brain uses the informationcollected by our eyes and interpreted by our sensory cortex to build a three-dimensional picture of the world with which we can interact. As anyone whohas hit a fast-moving baseball will know, our brain can process visual informa-tion and move our body in response to it in the blink of an eye.

Human senses and coordination are indeed impressive, but no more sothan many other animals. Where the human brain comes into its own is inits ability to solve problems. In humans, the ability to think through problemsand come up with solutions is the property of a small region within the lateralfrontal cortex. This small part of the brain acts as a central processing pointthat draws on memories stored in different parts of the brain. It can makeconnections with past experiences and relate them to the problem it is cur-rently faced with to find a solution. If there is no previous experience to drawfrom, the brain can propose likely solutions to new problems and then learnfrom the outcomes.

Memory, therefore, plays a crucial part in solving problems. The humanbrain has great capacity for memory. It is capable of storing and recallingmemories for over 100 years, should a person live that long. These memoriesare formed by the brain making new connections between its nerve cells, andit can do this at a phenomenal rate. The human brain can make and breakabout a million new connections every second. Given the brain’s ability tomake this many new memories, it is easy to see why the connections need tobe broken again if they are not needed. If we could not forget memories, ourbrains would fill up quickly and there would not physically be the space tomake new ones.

There are two types of memory that can form—short-term and long-termmemory. The short-term or the working memory is the ability to recall packetsof information learned within the last minute. The human brain can retain andrecall up to nine pieces of information in the working memory. This is one ofthe reasons why telephone numbers are typically restricted to nine digits, tomake them more memorable. The working memory is not well understood,but it is thought that several parts of the brain are involved: the frontal cortex,the parietal cortex, the anterior cingulate, and parts of the basal ganglia.

The long-term memory is a more permanent catalog of information storedin the brain. The key part of the brain linked with long-term memory is thehippocampus. Here, more permanent connections between nerves can be

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made following a process of reinforcement. A short-term memory thereforehas to be made permanent by repeated stimulus. Cramming the night beforean exam will enable a student to store enough information to pass the test,but the information will need to be reviewed again later if more permanentmemory is to be formed.

An important part of the reinforcement process happens at night when wedream. Although our bodies are asleep, our brains are still active. Dreaming isa critical part of the brain’s process to preserve and sort our memories. Evendaydreaming seems to be important. Although it is not involved with storingmemories, during the day the brain will run through its data bank of memoriesand try out hypothetical scenarios. It is thought that this constant stream of con-sciousness and wandering thoughts are important for developing our problem-solving skills. Our brain tests out what it will do in a certain situation before itcomes across the problem in real life, preparing itself for a range of new possibleencounters. When we really need to concentrate, though, this daydreamingproperty of the brain slows down, allowing us to focus on a particular task.

The brain’s ability to make and use memories in the way it does has beenfundamental for the success of the Homo sapiens. It can recall personal events(autobiographical memory), the words and grammar that make up our lan-guage skills (semantic memory), learned skills like walking (proceduralmemory), and our emotions toward people and things (emotive memory).Working with these memories, our brain can solve problems and interact withothers socially—both traits that have led to the success of the human species onthis planet.


The human brain works by information being passed from one part of thebrain to another through a hugely complicated array of nerve cells. The brainhas 100 billion nerve cells, each of which makes some 5000 connections toother nerves. It is these connections that make up our memory and ‘‘brainpower’’ thanks to the vast amount of information that gets passed from onepart of the brain to another. The brain has been described as a ‘‘neural net-work’’ because of the complex array of nerves through which information canflow. This is an incredibly powerful way of processing data. Computer scien-tists are beginning to replicate these neural networks in their attempts to createartificial intelligence and problem-solving machines. So far, artificial intelli-gence is rather limited. There is certainly a long way to go, but the humanbrain makes an excellent model to work from.

HUMAN LANGUAGE

Despite being a relatively weak, slow, and defenseless animal, there is nodenying the success of the human animal. What Homo sapiens lacks in certain


areas, though, it makes upfor in others. There areperhaps three key adapta-tions that have led directlyto the rise of humankind.The human brain is acomplex and powerfulorgan that allows us toprocess huge volumes ofdata and solve problems.Controlled by this largebrain, dextrous hands havebuilt and manipulated thetools with which we havemolded the environmentand shaped the world toour benefit. Finally, thereis our tremendous capacity for language. The ability to use and understandcomplex languages has given humans the ability to live socially and sharevaluable information on how to thrive in a world full of dangers andchallenges.

For centuries we have been fascinated by our own linguistic abilities, yet it isonly in the last few decades that real progress has been made in understandingthis fundamental human adaptation. For many years it was thought that lan-guage was a unique trait of humans. It is now known that this is not the case—all animals communicate with each other at some level, and certainly severalprimate species show what we can think of as a language—but certainly humanlanguage is the richest and the most powerful. With it we can pass on usefulinformation, we can deceive each other, and we can move people to tears orlaughter. Again, none of these traits are uniquely human, but they are notdisplayed to the same extent anywhere else in nature.

The language we predominantly use is based on sound. Air passing from ourlungs over our vocal cords vibrate them to produce audible sound. By tighten-ing and relaxing these vocal cords, as well as by altering the shape and positionof our mouth, lips, and tongue, these sounds can be shaped and formed intowords. The vocal cords themselves are not especially complex. They aretaut elastic membranes stretched out in the larynx, the part of the trachea(windpipe) known more commonly as the voice box. The vocal cords them-selves, then, are barely more sophisticated than a guitar string or a thin pieceof tissue stretched over a comb.

The position of the larynx is key to the human ability to make the complexsounds that can be formed into words. Early in our evolution the larynxdescended to a much lower position than in any other primate. One conse-quence of this is that it lengthened the pathway (the pharynx) through which

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Several views of human vocal cords at different points of vibra-tion in speech. [Omikron / Photo Researchers, Inc.]

both air and food pass before heading down either the esophagus (for food) orlarynx (for air). The downside is that this makes us much more prone to chok-ing than any other animal. The benefit, though, is that the enlarged cavity ofthe pharynx allows for the production of a wider variety of sounds. It isbelieved that the changes to the anatomy of the throat of our human ancestors,as well as changes to the shape of their faces to something we might recognizeas human, were the direct consequence of our ancestors evolving to walk ontwo legs. This led to a change in posture, lung position, and head position,which in turn led to changes in their shape.

In addition to physically being able to make sounds, humans must learn adictionary of words that they can recognize, use, and understand. These wordsthen need to be strung together in a way that makes the message clear—thereneeds to be a grammar. It is thought that the ability to develop and understanda complex grammar is what distinguishes human language from the languageand communication of other animals. Early human ancestors like Australopi-thecus (first appearing some 3.5 million years ago) had brains about the samesize of other apes—about 500 cc in volume. But as Homo species evolved, thebrain gradually increased in size to its current volume of 1400 cc, whichallowed for a more complex brain and greater cognitive ability. One of themost significant parts of the brain to enlarge was the cerebellum (literallymeaning ‘‘little brain’’) located at the base of the brain, above the spinal cord.The outer layer of this part of the brain is made up of grey matter and is calledthe cerebral cortex, where much of the human abilities of learning andcommunication derive. As with the brain as a whole, the cerebral cortex ismade from two identical-looking hemispheres. It is the left side, though, thatcontrols human language ability.

The cerebral cortex is important both for the production and comprehen-sion of language. However, other parts of the brain are also involved in lan-guage. Part of the temporal lobe, close to the part of the brain that controlshearing, is key to human comprehension of language. Part of the frontal lobecontrols the muscles of those organs involved with producing speech—thoseof the pharynx, larynx, tongue, and mouth. With such a complex arrangementof brain functions, it is thought that many steps must have been taken to evolvea brain capable of controlling linguistic ability, although some scientistsbelieve that only a very simple evolutionary step ‘‘rewired’’ the brain to movefrom simple to complex language ability. This is supported by the discoveryof one gene, called FOXP2, that appears to switch on nearly all human brainfunctions related to language comprehension and development. This gene isinvolved with activating other genes and could be key to the coordination ofall the genes that code for language.

With the ability to make words, understand them, and remember them,humans flourished as they could share information critical to their survival.Much like a queen bee that coordinates the behaviors of the hive using hor-mones, language in humans allows the species to operate as a society, rather


than simply as a group of individuals. Social groups can work in collaboration.With the complex languages of humans, the answers to complex problems canbe passed on from one generation to the next without the solution having to berediscovered time after time. What’s more, with the capacity for language,learning can take place without having to directly observe how a certain taskis performed. This method of learning and passing on information has beengreatly advanced with the invention of written language. Thanks to the writtenrecord, information can be passed between individuals on the opposite side ofthe earth and between generations, without people having to directly meet.


The evolution of the human brain, mouth, tongue, and larynx have enabledthe use of language, but the languages we speak are a product of what we hearas we develop as babies and children. Although the ability to speak a languageis innate in every human, the actual languages we speak are not hard-wired intoour brains; they must be learned. All newborn babies have the potential to speakany language. It is only our upbringing that determines which language(s) we areexposed to and which ones we learn from those we grow up around. It is perhapsnot surprising, then, that scholars of language estimate that there are nearly7,000 languages and dialects spoken today. Each of these languages represent asuccessful medium through which information can be passed from one personto another.

It is in the field of computing that humans have most attempted to recreatethis ability to transfer information based on a language with hard rules. Manycomputing languages have been developed that allow computers to carry outnew tasks learned from the information held in the form of a written computerprogram. Althoughmany remarkable things have been achieved with computers,they still lack the ability to comprehend very complex languages, which limitswhat tasks they can achieve. There is still a long way to go to develop languagesthat computers understand. Indeed, one of the goals is to develop computers thatcan understand human languages, allowing for easier interactions between manand machine as well as increasing the scope of what computers can do.

PLANT COMMUNICATION

Animals communicate with each other using sound, odor, and visual signals.This facilitates important behaviors between individuals—in locating food,evading predators, attracting mates, and in establishing social hierarchies.Plants are clearly not social organisms in the same way as many animals, sowe might not expect them to communicate with each other. Plants are indeedtalkative, though, and for good evolutionary reasons. Communication betweenrelated individuals can allow information to be passed back and forth to thebenefit of both.

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As with animals,information is sent fromone organ to anotherwithin a single plant.This is crucial for keep-ing everything workingand making sure differ-ent body parts work ina synchronized way.In animals, this internalcommunication is medi-ated by electricalimpulses sent throughnerves and with hor-mones that are carriedin the blood. Plants donot have nerves, but theydo use hormones. Thereare five major groups of

hormones in plants—auxins, gibberellins, cytokinins, abscisic acid, and ethyl-ene—all of which are essential for a plant’s growth and survival.

The five groups of hormone are responsible for the growth of the roots andstems, for flowering, seed production, and budding, for the ripening of fruit,and for senescence, the process by which leaves, stems, and branches die andfall off. All plant cells have specific hormone receptors to detect the presenceof any hormone. Once a hormone binds to a cell receptor, a chemical messagewill be sent from the cell membrane to the tiny organelles within the cell thatcontrol what it does. For example, a cell detecting an auxin hormone, whichcontrols stem growth, will begin to start dividing. The hormonal control ofplants is finely tuned thanks to millions of years of evolution, and it can resultin some impressive features. The intricate swirl of sunflower seeds that arearranged with mathematical precision are created by the deployment ofhormones with pinpoint precision.

Hormones mediate all communications within a plant. It is not surprising,then, that they are used to communicate between different plants as well.Hormones released into the air will influence the cells of plants of the samespecies just as if they had been produced internally because plants arecovered with pores for gas exchange, allowing the airborne hormones to per-meate their body. Throughout the year plants tend to go through thedifferent phases of their life cycle at the same time. To a degree this isbecause the plants are responding to the same environmental cues that trig-ger flowering, budding, leaf growth, and so on. But coordinated efforts byplants of the same species also happen, thanks to communication betweenindividuals.


Sea rocket, Cakile harperi. This plant can detect whether othersea rocket plants growing near it are non-related or relatedand control its growth accordingly so as to compete more orless competitively for nutrients. [Gilbert S. Grant / PhotoResearchers, Inc.]

This makes sense. Flowers and new leaves require a lot of energy to produce.They also happen to be attractive targets for hungry herbivores because they donot contain the poisons that older leaves have produced. If plants produce thisbumper crop all at the same time some will indeed be eaten, but predators willnot be able to devour the whole crop. This is really the same principle of animalsthat form huge flocks or shoals—there is safety in numbers. Before floweringand budding, then, plants will release hormones into the air that will trigger asimilar response in nearby individuals of the same species.

Synchronized leaf and flower production can be thought of as a preemptivebehavioral strategy for thwarting herbivores. However, plant communication isimportant in reactive behaviors, too. In many species of tree, an individual that isunder attack from herbivores will put out a ‘‘distress call’’—again, by releasingvolatile hormones into the air. Neighboring trees of the same species that detectthe hormonewill then putmore energy into producing their defenses against pred-ators. They will produce much higher levels of the tannins, alkaloids, and otherpoisons that make their leaves and small branches unpalatable to herbivores. Theuse of such a distress call means that individual plants do not have to produce highlevels of defenses all the time. Bitter-tasting chemicals require a lot of energy tomake, which could otherwise be usefully employed for growth. Again, there areparallels with animal societies. Meerkats will appoint only a few individuals of thegroup to act as sentries. The others can then go about their business without hav-ing to worry about being vigilant against possible threats. If the sentries spot apredator they will give a call, and the rest of the group will scatter.

This level of plant communication is impressive, but it is not the wholestory. Some plants are even able to detect how closely related a particular indi-vidual is. This has been observed in the sea rocket. As with animals that candetect kin, sea rocket plants show preferential treatment to those who are moreclosely related because of the evolutionary benefits of acting altruisticallytoward kin. Growing next to unrelated plants, the sea rocket will put out manynutrient-grabbing roots. If it detects family nearby, however, it puts out muchfewer roots, even to the cost of depriving itself of valuable nutrients. Previ-ously, this sort of behavior was only known in animals. It is assumed that thesea rocket must be detecting and analyzing some hormone released into theair or soil, but it is not known exactly what. Similar kin-related behaviors havebeen found in other species.

Plants, then, do talk to one another. By extending their internal communi-cations network that regulates their growth to communicate with others,plants can enjoy the same social benefits of living in groups as animals. Beingrooted to the ground need not mean living in isolation.


The communication of plants in response to attack by herbivores is particu-larly interesting to farmers of cereal crops and fruit trees. Farmers are keen on

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seeing that their crop is not destroyed by herbivores, but increasingly they arereticent to use chemical pesticides. If the genes controlling the distress call andresponse behavior could be isolated and inserted into the crop species, thiscould be a helpful solution to some of the risks associated with organicfarming.

BEE DANCE LANGUAGE

It was long thought that communica-tion and language in humans was thetrait that set us apart from other animals,and that we were truly different from allother living organisms. It is now knownthat this is not true. Many animals, notto mention plants and bacteria, havesophisticated languages with which toimpart useful information.

One of the more elegant and fasci-nating forms of communication innature is the dancing language of thehoney bee, Apis mellifera. With this lan-guage, workers returning from foragingtrips are able to communicate to therest of the hive how far away and inwhat direction food lies as well as howwell-stocked the source is. With no

vocal capability, this language is a multidimensional form of communicationthat involves mime, sounds, and smells. It is what is known as a multichannelsystem of communication—information is given in a variety of ways, muchlike our spoken and written language.

Thanks to painstaking research from an Austrian behavioral ecologist calledKarl von Frisch, we know that the honey bee language is made up of threebasic mimes or ‘‘dances’’ that tell the bee’s fellow workers where to find food.All the dances are performed on the vertical surface of the hive’s honeycomb.When a bee performs a dance, it attracts the attention of fellow workers whoare known as followers, as they will use the information given to retrace thedancer’s movements to the food.

The first of the dances is called the ‘‘round dance,’’ which gives informationabout food sources within 80 feet (25 m) of the hive. This is a simple dance thatcomprises a series of runs in a circle with frequent changes in direction. Thefollower workers who are watching this dance will touch the dancing bee withtheir antennae in order to taste the nectar that the dancing bee regurgitatesfrom time to time. By tasting, the followers can learn the quality of the food.Food quality is also determined by how vigorously the worker dances and


The waggle dance shown by honey bees. Theangle and the frequency of the dance showsthe direction and distance to good sources offood. [Lena Untidt / Bonnier Publications /Photo Researchers, Inc.]

how frequently she changes direction. From this information, the followerscan build up a good idea of the calories that are available at the advertised foodsource. The round dance does not convey the direction of the food. As it signi-fies food within 80 feet (25 m) of the hive, followers can find it easily enough byflying away in an increasing spiral with the hive at its center.

For food sources that are greater than 330 feet (100 m) away, the worker beeperforms the ‘‘waggle dance,’’ in which the dancer follows a path shaped like afigure-eight that has been slightly squashed. On the loops around the figure-eight the worker will keep her body straight. When she gets to the longstraight in the middle of the squashed figure-eight she will rapidly waggle herabdomen from side to side and buzz her wings, making a high-pitched sound.It is the length of the straight run and the number of waggles in it that com-municates the distance of the food source from the hive. The followers canmeasure the distance the worker is moving on the honeycomb by countingthe number of cells that she passes over. This directly relates to the distancethey will have to travel to find food. As before, the vigor with which the workerdances, the frequency of her waggles, and the frequency of her high-pitchedbuzzing all convey information about the quality of the food.

As the waggle dance gives information about food that is over 330 feet(100 m) away, it needs also to give information about the direction in whichthat food lies. It would be a waste of energy for a follower to have to exploresuch a huge circumference even if it knows how far from the hive the foodsource is. Directional information is given by the angle, from the vertical, atwhich the straight part of the dance (where she waggles her abdomen) isperformed. This matches the angle between the sun, as seen from the hive,and the direction of the nectar source. This information can be given by theworker because she can note and memorize the position of the sun. Amazingly,with her in-built sense of time she can also compensate her dance to accountfor the movement of the sun as the minutes pass.

For distances between 80 feet (25 m) and 330 feet (100 m), the worker willperform an intermediate dance, which has elements of both the round danceand the waggle dance, giving direction and some idea of distance. With thesethree dances, the social honey bees can share information that enables the hiveto exploit nearby food sources as a cohesive society rather than as an uncoordi-nated collection of individuals.

The honey bee’s dancing language is not only restricted to informationabout where food lies. Workers also perform a ‘‘vibrational’’ dance where theyvibrate their bodies up and down very quickly (as opposed to the waggle dancein which the worker vibrates its body from side to side). This tells fellow work-ers where on the comb a waggle dance is taking place. These directing dancestake place more frequently at times when there is a greater demand for foodand more workers need to be recruited for foraging.

As with human language, honey bee language has evolved regional dialects.Italian honey bees change from the round dance to the waggle dance when

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food is around 115 feet (35 m), whereas Austrian bees make the change at260 feet (80 m).When scientists artificially move Italian bees to Austrian hives,confusion reigns. The bees cannot understand each other, and they head offlooking for food in the wrong place.


The ability of honey bees to learn from their hive-mates the location of afood source and then navigate toward it based on the information is inspiringalgorithms to be developed that would allow small robots to learn and navigatein the same way. This work is having valuable input into the development ofartificial intelligence and navigation systems that would allow robots to findtheir way around and interact with real environmental conditions.

BACTERIAL CONJUGATION

In animal groups and societies,humans included, behaviors can betaught and passed from one individualto another. By copying behaviors shownby other individuals, important infor-mation can be passed throughout agroup. Successful pieces of informationsuch as how to get certain foods or howto treat certain illnesses quickly spreadthrough the population because of thebenefits gained from the knowledge.This process of learning is widespreadin animals and is responsible for a rangeof behaviors seen in nature—fromyoung male birds learning songs fromtheir neighbors to capuchin monkeys

learning to crack nuts with stones from others in the group.Other species are not able to learn useful behaviors in this way. Plants, for

example, do not have the sense organs or brains to process the informationand incorporate it into their own daily lives. Although they use a differentmethod from animals, bacteria can share information from one individual toanother, although the information they share is coded onto their geneticmaterial. Unlike animals, single-celled bacteria can share DNA with eachother and pass on the useful genes held within it.

All bacteria carry the genes that are essential for their survival on what isknown as the bacterial chromosome. Some individual bacteria, however, carryan additional packet of DNA called a plasmid, which is a short piece of DNAthat is looped into a circle rather than being twisted together in a strand to


A transmission electron micrograph showingbacterial conjugation by Escherichia coli. DNAis passed from one bacterium to anotherthrough thin tubes called sex pili. Antibac-terial resistance genes can be passed quicklyamong bacteria in this way. [Dr. Linda M.Stannard, University of Cape Town / PhotoResearchers, Inc.]

form a chromosome. Genes on the plasmid are not essential for life, whichexplains why some individual bacteria can survive without them. The genesstored on this extra loop of DNA, though, can give the individual a hugeadvantage when it comes to coping with the pressures of their environment.

One of the most important genes that can be found on bacterial plasmidsgives resistance to antibiotics. Antibiotics are designed to kill bacteria, whichis why they are so useful in fighting disease. To counteract this, an antibiotic-resistance gene in the plasmid codes for an enzyme (a protein molecule) thatdestroys or inactivates a particular antibiotic. Plasmids that carry these genesare known as R-plasmids, which stands for ‘‘resistance plasmid.’’ One of themore common R-plasmids can be found in the bacteria Staphylococcus aureus.Some of these bacteria have several genes for antibiotic resistance on theirplasmid that gives them multiple resistance to antibiotics, hence the morecommon name for the bacteria, MRSA (multi-resistant Staphylococcus aureus).

MRSA perhaps would not be the problem it is in hospitals if the R-plasmidswere passed on only when a bacteria divided to make a new copy of itself.However, bacteria are able to replicate and pass on plasmids from one toanother without having to divide. This is done through direct cell-to-cell con-tact via a tiny tubular organ called a sex pilus. Sex pili are thin, hollow filamentsthat hang from certain bacteria. They are made from a unique protein calledpilin and are about 3–10 nanometers in diameter. Typically, they can only beseen under powerful electron microscopes. Individuals that have sex pili arecalled donors (or F+ bacteria: the F stands for ‘‘fertility’’). Donors use their pilito form a bridge to other bacteria (called recipient or F− bacteria). Theypenetrate the recipient’s cell wall and transfer a copy of their plasmid to it.The process takes about 90 minutes to complete.

The process, bacterial conjugation, has been likened to a primitive form ofsex, although really it is quite different from the fusion of sperm and egg cellsseen in animals and plants. However, bacterial conjugation is an extremelyimportant evolutionary process for species of bacteria that are capable of it.Useful genes on a plasmid moving from one individual to another can spreadrapidly through a population, giving a selective advantage to those that possessit. What’s more, although it is much rarer, some genes from the main bacterialchromosome can be passed from one to another, again allowing for usefulgenes to be passed on within the same generation.

It is unlikely that bacterial conjugation has evolved to spread useful genes torelated individuals of the same species. Instead, it should be thought of as aparasitic piece of DNA that has evolved to make use of bacteria to pass copiesof itself from one bacterium to another. The plasmid is just like a virus in thatrespect. Typically, some 40 genes on a plasmid will code for the production ofthe sex pilus and the process of replicating and passing on the plasmid itself.This means that the recipient of the plasmid now has the ability to producesex pili and pass on the DNA to another bacterium. From the point of viewof the plasmid, its evolutionary success is measured by how many copies of

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itself it can produce. This is the basic idea around the selfish gene theory ofevolution. It so happens that certain other useful genes have become incorpo-rated into the plasmid and have come along for the ride.

However we think of the evolution of plasmid transfer in bacteria, its suc-cess is undeniable and the benefits to the bacteria themselves are huge. It isextremely common in nature and happens in many species of bacteria. Conju-gation may even happen between individuals of different species, and it haseven been reported as occurring across kingdoms. For example, there hasbeen observed conjugation between a bacterium (Escherichia coli) and a yeast(Saccharomyces cerevisiae) and even between E. coli and mammal cells.


The most significant impact of this adaptation is in the rise of bacteria likeMRSA that are resistant to several types of antibiotic—the so-called super-bugs. MRSA killed 18,000 people in the United States in 2005, and it is likelythat the number of MRSA deaths will be higher in coming years. The solutioncould well lie in the defense mechanisms of the bacteria themselves. Since allbacteria can potentially receive DNA from any other bacteria species, theyhave evolved a way to block unwanted DNA transfers. A similar process hap-pens in animal and plant cells to resist certain viruses or parasitic sections ofDNA called transposons, which can wreak havoc if they insert themselvesinside the middle of a crucial gene, rendering it useless.

A bacteria will store a memory bank of dangerous pieces of DNA, and whenthese dangerous genes are detected they are destroyed. Over time, a bacteriumlearns and builds up a greater number of templates of these dangerous genes.In a way, it is a defense mechanism very similar to our immune system—ourbodies need an initial infection before it recognizes a dangerous pathogen.When we are infected again our immune response recognizes the pathogenand kills it quickly. The aim, therefore, is to artificially create a template forthe MRSA genes and use them to coat hospital surfaces. This, in theory,should prevent widespread exchange of the MRSA genes between bacteria.

CULTURE

It was once thought that there were many traits that could be considereduniquely human—that there were certain behaviors that separated humankindfrom the rest of the animal kingdom. It is now realized that many of these pur-ported exclusively human traits can also be found in other animals. For exam-ple, it is not only humans who communicate with each other. All animalscommunicate in some form or another—not to mention plants and even tiny,singled-cell bacteria. Is there anything left that is unique to humans? It hasbeen suggested that one of these may be the rich cultures that have arisen inevery human population—the art, literature, religion, and cuisine that have


been invented and passed on among individuals living together. However, itseems that even culture is an adaptation found elsewhere in nature.

Culture is really any behavior that develops within a group of individualsand is passed on from one to another. There is no doubting the importanceof cultural behaviors in human societies. By bringing pleasure, guidance, andsolace, culture often creates cohesion and togetherness in society—not tomention the important behaviors that are learned and shared so the wholesociety can benefit from them. Medicinal cures, farming practices, and otheruseful information can spread to the benefit of the whole social group. Othercultural behaviors are important in identifying individuals as belonging to thesame social group. A unique greeting can identify an individual as a friend withwhom another can collaborate.

Although we may not notice them, cultural behaviors are quite common innature. The ocean-bound cetaceans, dolphins and whales, have rich cultures.Killer whales fall into different social groups that have very different behaviorsand customs. Transient groups are typically made up of one female and two orthree offspring. Resident groups are much larger. The two groups differ intheir diet, vocal calls, preferred habitats, and even in color and shape. Killerwhales are able to eat more or less anything that comes their way, but thetwo groups have particular tastes. Residents eat only fish, whereas transientsavoid fish and feed only on ocean mammals—seals, sea lions, porpoises,dolphins, and even other large whales.

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A chimpanzee using a stick to get food. These behaviors are taught and passed on fromone individual to another. [Adam Jones / Photo Researchers, Inc.]

The two killer whale societies live in the same waters and are able to inter-breed, although there is evidence to suggest that they choose not to. It is liketwo human societies that live nearby but who choose to have nothing to dowith each other. All the traditions of the two groups are learned by the youngfrom their parents. Such is the incompatibility of the two groups that theyare fast becoming distinct species.

It is unclear how such traditions evolve, but as with human societies thesecustoms create a cultural identity that can lead to distinct social divisions thatare hard to overcome. Some cultural behaviors, however, have a more practicaluse. Tool-making in humans was another trait thought to be unique in the ani-mal kingdom, but it is now known to occur in several other species as well.Chimpanzees use rocks to crack nuts and thin plant stems to fish for termites.Individuals will methodically strip the leaves from a stem and feed it into atermite mound so termite soldiers bite the probe thinking it is an invader.The chimps then withdraw the stem and graze on the juicy termites that tena-ciously cling on. These tool-making skills are a cultural behavior passed onwithin a social group to the benefit of all.

Given that apes like chimpanzees are so closely related, evolutionarily, tohumans it is perhaps of little surprise that they show tool-making skills akinto humans. Perhaps one of the most ingenious tool makers is only very dis-tantly related to humans, though. The New Caledonian crow shows tremen-dous tool-making skills to solve whatever problem it may face. Using thelong, narrow leaf from the pandanus tree as a basic material, the New Caledo-nian crow can fashion a range of tool using its beak. It will fashion differentlyshaped hooks and rakes to extract insects from different crevices. The crow’stool-making skills and its remarkable problem-solving brain seems to workvery much like the human brain. For example, both species’ brains havedistinct ‘‘sides.’’ The crows even show ‘‘handedness’’ just like humans. Mostindividuals are right-beaked and will use the right side of the beak to createtheir tools.

Important skills such as these can be passed on from individual to individualin a society, which benefits all in the group. Similar benefits can be achievedfrom more abstract behavior. Laboratory tests have shown that rhesus mon-keys and rats both will refuse a gift of food if it means causing harm (throughan electric shock) to another individual in the group. This suggests a moralbehavior, although it can be seen as an extension of other altruistic behaviorsto related individuals. This can be taken to the extreme of animals in a groupfeeling emotion for one another. Elephants are known to care for injuredmembers of the herd. Magpies perform funeral rituals for members of thegroup who have died, suggesting grief. Individuals in the group will first checkto see if an individual is indeed dead by prospective pecks of the beak and willthen swoop around the corpse, giving a distinctive cry.

The evolutionary significance of cultural behaviors may not be immediatelyclear, especially the emotional ones. All group behaviors, though, whether


ritual or practical, are key to maintaining the cohesion of a social group. Forthose animals that have evolved a social structure, there is a clear evolutionaryadvantage over a solitary life. Individuals within a group benefit from sharedresources as well as the protection a group offers. Culture lies at the heart ofthese social groups and is what keeps them together.


It seems strange to think of humans learning any cultural behaviors fromanimals, but it does happen. Humans have copied chimpanzees’ behavior ofeating charcoal (from burnt trees) to settle their stomach after eating poison.This would probably have been well known in human hunter-gatherer soci-eties, but has been learned again in some cases by observing our chimpanzeecousins. Indeed, observations of the medicinal remedies that certain animalsuse have led in some instances to new pharmaceuticals being extracted fromcertain plants—an example of cross-species cultural transfer.

DNA

In the mid-nineteenth century, the pio-neering work by Charles Darwin and hisfellow naturalists set the scene for ourunderstanding of evolution. Darwin,through his observations of similar-looking species, suggested his theory thatmodern species were descended from olderancestors and that species could evolve andadapt in response to selection pressuresfrom their environment. The evidenceDarwin relied on was the degree of similar-ity in groups of species he assumed shared acommon ancestor. The key to the theory,Darwin knew, was that there must be somehereditary material passed from one gener-ation to the other that contained the infor-mation that made an individual what it is.Only through changes to this informationcontained in hereditary material could adaptations arise and improve.

Darwin’s assumption about a hereditary substance was right. Following afrantic period of research by several individuals the structure of deoxyribosenucleic acid (DNA) was revealed on February 28, 1953, by James Watsonand Francis Crick. It is now known that DNA stored in every cell of an organ-ism contains all the information needed for that cell to grow, divide, and func-tion. Indeed, each cell contains the entire DNA blueprint for the growth and

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Adigitalmodel ofDNAbased on data gener-ated by x-ray crystallography, a process usedto determine the structure of a molecule.[Kenneth Eward / Photo Researchers, Inc.]

function of the whole organism. What’s more, it can be passed from one gen-eration to another via sperm and egg cells that combine to make an embryo.Successful adaptations coded for by an individual’s DNA are thereforepreserved and passed on to its offspring.

What Watson and Crick discovered was that DNA is a double helix, twostrands woven about each other. Each strand of DNA mirrors the other half.This is important because it means that each cell carries a spare copy of theinformation stored on its genetic material. DNA is constantly being copiedand duplicated in our bodies, and mistakes do happen. The double helixreduces the risk that these mistakes are harmful. Tiny molecular machinespatrol DNA, checking each half against its neighbor. If there is a mistake inone of the strands it can be corrected and no harm is done.

There is a great deal of DNA held in our cells. If it were unravelled andstretched out, the DNA from all the cells of an average human being wouldstretch to the moon and back 8,000 times. To make the DNA compact tofit in our cells, the double helix of DNA is coiled up even further and storedas discrete packets called chromosomes. Humans have 46 chromosomes(in 23 pairs), although organisms can have as few as just one chromosome oras many as 1,200. What is important, though, is the information coded onthe DNA. Just as the whole of the English language is created from only 26 let-ters, the language of DNA is written with four letters. A near infinite amountof information can be held on the molecule by simply rearranging thesequence of these four basic units of information. These units (or bases as theyare called) are molecules called adenine, cytosine, guanine, and thymine, or A,C, G, and T for short.

The bases are arranged in ‘‘words’’ of three letters. Each of these wordscodes for a particular amino acid, the building block of proteins. A sequenceof DNA will therefore be code for a certain sequence of amino acids that willmake up a particular protein. The whole process means that a sequence ofDNA bases can be read by tiny molecular machinery and translated into athree-dimensional protein molecule. The proteins coded for by DNA ulti-mately control everything in the body. They are responsible for making themolecular building blocks that make up an organism’s body and joining themtogether. They also control the reactions that are constantly occurring thatkeep an individual’s body working properly.

Most people are familiar with the longer stretches of DNA that make upgenes. Genes contain information for proteins that work together in such away as to produce a whole array of traits from eye color to blood type—genescode for everything that makes an organism what it is. It is random changes tothese genes (mutations) as they are passed from one generation to the next thatgives rise to changes in body or behavior. Beneficial mutations that increasethe survival of an individual or the number of offspring it leaves will tend toremain in the gene pool, whereas harmful mutations are lost. This is howevolution works.


It is easy to see how small changes to a gene can make it better over thou-sands of years of evolution. For example, natural selection will have graduallyled to the improved eyesight of different birds of prey. But how can a new genebe produced? How can natural selection create a new trait altogether? Thisseems particularly difficult, as most genes code for traits that are essential foran individual to survive, so any significant changes to them would decreasethe chances of survival, not improve them.

During cell division, not only can some of the bases be changed, but a wholegene can be replicated. If this happens during the production of sperm or eggcells, the resulting offspring could have two copies of a gene for eye colorinstead of just one. One copy will continue to code for blue eyes as before,but the new copy now has no role to play at all. With no function to perform,this duplicate gene is free to change randomly into another gene coding for acompletely different trait entirely. This process seems to be quite common.Humans have 400 genes for smell receptors, all of which appear to haveevolved from just two genes that were found in our fish ancestors that lived450 million years ago. They seem to be duplicates that have evolved to performa slightly different role. Through this process, new genes coding forcompletely different traits could easily evolve.

DNA is not just made up of genes, though. Quite a large part of any species’genome is made up of DNA that seems to have no role at all. These sectionshave been called ‘‘junk DNA,’’ but that might be a bit of a misnomer. Althoughjunk DNA may directly not code for a particular trait, it is far from useless.Some junk DNA is involved with the coiling of DNA into chromosomes, andothers may indeed be involved with the formation of memories. Memoriesare stored as connections made between nerve cells in the brain. When thesenerve cells divide, the memory held within the cell is preserved in the newcopy. There is evidence to suggest that this happens by adding molecular‘‘caps’’ to the cell’s DNA when the original memory is formed. When thenerve cell divides, its DNA will replicate as with any cell division. The DNAcaps will also be replicated so the new cell will have the same memory storedwithin it as the parent cell. That way the memory will be preserved even asnerve cells die and are replaced.

Other sections of DNA are involved with directing the molecular machinesthat read and translate the information held on a stretch of DNA. Some DNAis therefore used as a marker to show where the machines should start and end—they are a little like chapter headings. Similarly, some sections of DNA codefor information used to enhance the expression of other genes. An importantreporter gene (as these sections of DNA are called) that has been discoveredrecently goes under the name HACNS1. This reporter gene is particularlyactive in humans and is responsible for the growth and development of ouropposable thumb. It is suggested that evolutionary changes to the humanthumb came about thanks to the evolution of the HACNS1 reporter generather than on the thumb gene itself.

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This book only scratches the surface of how DNA works, but there is nodoubting its importance. It is the key to storing and communicating all theinformation required to create and sustain life. Crucially for the process ofevolution it is made in a way that allows it to change, which, through naturalselection, can lead to the creation of thousands of remarkable adaptations innature.


There are a number of weird and wonderful uses to which DNA is beingput. Perhaps one of the strangest involves exploiting the double helix structureof DNA in the field of nano-technology. Because each strand of DNAmatchesits partner, scientists are exploring whether it can be used as a microscopic‘‘velcro’’ strip that can be used to fasten and separate nano-particles. To date,these attempts have not been very successful, and it is not clear exactly whatuses it could be put to, but there are engineers out there who are trying tofind out.

Perhaps the most fruitful use will be in the field of computing. A branch ofcomputer sciences is exploring the use of fiber optics to transfer informationin processors rather than electricity. To achieve this, some computer scientistsare embedding a light-storing molecule called chromatophores in strings ofDNA. Chromotophores absorb and pass on light, and so they are perfect forcreating a microscopic fiber optic cable. And DNA is the right size to supporta thin enough string of chromatophores to fit on a computer chip. The realadvantage of DNA, though, is that it is self-repairing and the machinery toachieve that already exists in nature, so engineers do not have to come up witha design from scratch.


FURTHER READING

In writing this book I have drawn on a number of sources of information. I rec-ommend the following to further explore what you have read in this book, orindeed to discover other remarkable adaptations that can be found in nature.I have included some Web-based resources that I have found especially usefuland interesting. However, I would advise that anyone carrying out anyresearch on the Internet to exercise caution. The quality of information ontheWeb is extremely variable, and often you will find interesting but nonethe-less inaccurate information that is little more than a perpetuated myth. Alwayslook for further references for the information found on the Web—preferablyreferences to reputable journals that publish or review research in the field youare covering. That said, the Internet is an excellent place to start your studies.

BOOKS

Attenborough, D. The Private Life of Plants. London: BBC Books, 1995.. The Life of Birds. London: BBC Books, 1998.. The Life of Mammals. London: BBC Books, 2003.. Life in the Undergrowth. London: BBC Books, 2005.. Life in Cold Blood. London: BBC Books, 2007.

Beattie, A. and P. R.Ehrlich. Wild Solutions. New Haven and London: Yale UniversityPress, 2001.

Bryson, B. Mother Tongue: The English Language. London and New York: PenguinBooks, 1991.

Darwin, C. On the Origin of Species: 150th Anniversary Edition. Penguin Group, USA,2003.

Dawkins, R. The Extended Phenotype. Oxford: Oxford University Press, 1993.

Dennett, D. C. Darwin’s Dangerous Idea. London and New York: Penguin Books,1996.

Diamond, J. Guns, Germs and Steel. London: Vintage, 2005.Foelix, R. F. The Biology of Spiders, 2nd edition. Oxford and New York: Oxford Univer-

sity Press, 1996.Hickman, C., Jr., L. S. Roberts, , and A. Larson. Integrated Principles of Zoology, 13th

edition. Boston: WCB Publishing/McGraw-Hill, 2006.Margulis, L. andW.H. Schwartz, Five Kingdoms. 3rd edition. New York: Freeman and

Company, 1998.Moore, R., R. M. Clark, , D. Vodopich, and K. R. Stern. Botany. Dubuque, IA:

William C. Brown Publishers, 1995.O’Toole, C. Alien Empire: An Exploration of the Lives of Insects. London: BBC Books,

1995.Ridley, M. Evolution. 3rd Edition. Oxford: Wiley-Blackwell, 2003.Shuker, K. P. N. The Hidden Powers of Animals: Uncovering the Secrets of Nature.

London: Marshall Editions, 2001.

USEFUL INTERNET SITES AND JOURNALS

LiveScience, www.livescience.com.Nature, www.nature.com.New Scientist, www.newscientist.com.Public Library of Science, www.plos.org.Science, www.sciencemag.org.Scientific American, www.scientificamerican.com.Trends in Ecology and Evolution, www.trends.com/tree/default.htm (subscriber

service).

SELECTED SCIENTIFIC PAPERS

Autumn, K., M. Sitti, Y. A. Liang, A. M. Peattie, W. R. Hansen, S. Sponberg,T. W. Kenny, R. Fearing, J. N. Israelachvilli, and R. J. Full. ‘‘Evidence forVan der Waals Adhesion in Gecko Setae. PNAS 99 (19): 12252–12256

Bell, K. S., P. D.W. J. Aw, and N. Christofi. The genus Rhodococcus. Journal of AppliedMicrobiology 85, 195–210.

Berry, R. M. and J. P. Armitage. How Bacteria Change Gear. Science 320 (2008): 1599–1600.

Blair, K.M., L. Turner, J. T. Winkelman, H. C. Berg, and D. B. Kearns. A MolecularClutch Disables Flagella in the Bacillus subtilis Biofilm. Science 320 (2008): 1636–1638.

Bradbury, J. Nature’s Nanotechnologists: Unveiling the Secrets of Diatoms. PloSBiology 2 (10) (2004): 1512–1515.

Bramble, D. M. and D. E. Lieberman. Endurance Running and the Evolution ofHomo. Nature 432 (2004): 345–352.

Bryner, J. Night Vision: How Snakes Get Clear Picture of Prey. LiveScience 10 (2006).Callaway, R. M. and B. E. Mahall. Plant Ecology: Family Roots. Nature 448 (2007):

145–147.

192 FURTHER READING

www.livescience.com

www.nature.com

www.newscientist.com

www.plos.org

www.sciencemag.org

www.scientificamerican.com

www.trends.com/tree/default.htm

Chaix, R., C. Cao, and P. Donnelly. Is Mate Choice in Humans MHC-Dependent?PLoS Genetics 4 (9), 1–5, 2008.

Choi, C. Q. Bat’s Wrinkly Face Improves Sonar. LiveScience 28 (2006).Copley, J. Springtime in the Abyss. New Scientist 2525, 44–48, 2005.Frederickson, M. E. and D.M. Gordon. The Devil to Pay: A Cost of Mutualism with

Myrmelachista Schumanni Ants in ‘Devil’s Gardens’ is Increased Herbivory onDuroia hirsuta Trees. Proceedings of the Royal Society B 274, 117–1123 (2007).

Frederickson, M. E., M. J.Greene, and D.M. Gordon, ‘Devil’s Gardens’ Bedevilled byAnts. Nature 437 (22) (2005): 495–496.

Fox, D. The Secret Life of the Brain. New Scientist 2681 (2008).Geiger, B. Deep Heat. Current Science 91 (13) (2006): 8–9.Gross, M. Extreme Olympics. New Scientist. 2336 (2002): 1–3.Gutin, J-A. C. A Brain That Talks—Neurological Evolution of Human Language.

Discover (1996).Hansen, W. R. and K. Autumn. Evidence for Self-Cleaning in Gecko Setae. PNAS

102 (2) (2005): 385–389.Herberman, E. Cave of Goo! Current Science 84 (5) (1998): 8–9.Hooper, R. ‘Medicine Cabinet’ Found in Wasps’ Antennae. New Scientist.Jones, D. Uncovering the Evolution of the Bacterial Flagellum. New Scientist (2008):

2643.Kenneally, C. So You Think Humans Are Unique? New Scientist (2008): 2657.Le Page, M. Recipes for Life: How Genes Evolved. New Scientist (2008): 2683.Miller, G. Bestial Bugs. New Scientist (2001): 2318.Minkel, J. R. Pictures of Nerve Cells Hint at Changes Underlying Memory Forma-

tion. Scientific American (2001).O’ Donoghue, J. How Trees Changed the World. New Scientist (2007): 2631.Peterson, I. A Biological Antifreeze; Antifreeze Proteins Found in the Blood of Polar

Fish Alter the Way Ice Crystals Grow. Science News (1986): 22 .Pettigrew, J. D., P. R. Manger, and S. L. B. Fine. The Sensory World of the Platypus.

Philosophical Transactions of the Royal Society of London B 353 (1998): 1199–1210.Powell, D. Memories May Be Stored on Your DNA. New Scientist 2684 (2008).Sane, S. P. The Aerodynamics of Insect Flight. The Journal of Experimental Biology 206,

4191–4208.Shain, D. H. The ice worm’s secret. Alaska Park Science, Kenai Fjords Special Issue 3 (1)

31 (2004).Srygley, R. B. and A. L. R.Thomas. Unconventional Lift-Generating Mechanisms in

Free-Flying Butterflies. Nature 420, 660–664.

FURTHER READING 193

INDEX

Acinonyx jubatus, 64Adhesive, 98–100, 102–103Aerial roots, 36, 38Aerofoil, 56, 58, 60–62Agriculture, 12, 38, 75, 107Algae, 3–6, 48, 70, 95, 112, 126, 132Allele, 156Alloys, 80Altruism, 186Alula, 59–60Alvin, the, 4Alzheimer’s disease, 54Amazonian rainforest, 17, 147–148Amino acid, 41, 53, 105, 133, 188Ampullae of Lorenzi, 148Amyloid, 52Anhydrobiosis, 49–51Animal skins, use of, 26, 55, 80Ant, 16–18, 45–47, 77, 83, 123, 158,161

Antenna: and antibiotics, 160–162;insect, 150–151, 160–162, 171, 180

Anterior cingulate, 173Anti-glue, 40Antibacterial, 45, 98, 116, 122Antibiotics, 45–47, 77, 183Antifreeze proteins, 31–32

Antifungal, 45–46, 120Antioxidant, 52–53Arachnocampa luminosa, 127Arthropoda, 12, 83, 86–88Artificial dermis, 93Artificial intelligence, 174, 182Ascaris lumbricoides, 43ATP, Adenosine Tri-Phosphate, 4, 10–11, 48–49, 76

Aviation, 56–57

Bacteria: chemosynthetic, 7; marine,100; photosynthetic, 5; symbiotic, 49;thermophilic, 28–30

Bacterial conjugation, 11, 182–184Bacterial flagellum, 76–77Basal ganglia of brain, 173Basking, 13–14, 153Bat, 145–147, 158Batumen, 121Beaver, 117–120Beaver dam, 118Beaver lodge, 117, 120Bee nest, 120–122Behavior, human mating, 155–157Bioceramics, 94–95Biofilm, 177

Bioluminescence, 21–24, 127Biotechnology, 38Bird nest, 115–117Black-smokers, 7Blind spot, 141Blood antifreeze, 31–33Blood type, 156–188Blubber, 34, 90Bluefin tuna, 66–68Body odor, 155–157Boid snake, 151–153Bombardier beetle, 14–16Bone, 40, 59, 64–65, 70, 79, 80, 82, 84–87, 89, 95, 100, 117, 146; compact, 85–86; spongy, 85

Bone marrow: red, 85–86; yellow, 85–86Bowerbird, 117Brachinus, 15Brachyhypopomus pinnicaudatus, 147Brain, human, 27, 47, 52–54, 59, 63, 72,79, 122, 140–144, 148–149, 152, 154,157, 160–165, 171–177, 182, 186,189

Breathing, 39, 43, 62, 64Breathing devices, artificial, 26–27Brock, Thomas, 29Brood comb, 121–124Brown fat, 14BSE, Bovine spongiform encephalitis,52, 54

Building, human, 86, 95, 107–109Bull ant, 45–47Bullet-proof vest, 81, 84Buprestid beetle, 149–152

Calcium phosphate, 84Calvin Cycle, 4Cambium, 113–114Camouflage, 23–34, 88, 90, 116, 152,163

Cancer treatment, 24, 28, 41, 42, 44,127, 131

Capillary action, 101, 114Carbohydrate, 3, 4, 6–7, 9, 96Carbon-infused rubber, 139Carotenoids, 90Cartilage, 84, 93, 145Castor canadensis, 117–119

Catabolism, 8, 10–11Cell membrane, 11, 19, 29, 35, 71, 72,115, 149, 152–153, 160–161, 178

Cellulose, 80, 88, 113Ceramics, 95Cercariae, 71–72Cerebellum, 176Cerebral cortex, 176Cerumen, 121Cheetah, 64–65Chelicerae, 98Chemoreceptor, 150, 154Chemosynthesis, 6–8, 21Chemotaxis, 77Chitin, 43, 86–89Chlorophyll, 3–4, 37Chloroplast, 5, 10, 158Cholesterol, 40Chromosome, 182–183, 188, 189Chronic pain, treatment of, 131CJD (Creutzfeld-Jakob disease), 52, 54Climate-control, 111Cochlea, 146Cold-blooded animals, 12–14, 47, 152Collagen, 84–86, 92, 96Common swift, 59Communication, 169–190; in bees, 180–181; human, 91, 169–171; in plants,177–179

Computing, 139, 177, 190Concrete, 95, 108–109Cone, photoreceptor, 140–141, 166Coral polyp, 125–126Coral reef, 124–126Cordage, 80Cornea, 140–141Counter-current heat exchange, 14Crick, Francis, 187–188Crops, cold-resistant, 32Crustacean, 12, 86, 163Cryogenic storage, 33, 49Cryptobiosis, 50–51Cryptochrome, 159Cueva de Villa Luz, 8Culture, 184–187; in chimpanzees,185–187; in elephants, 186; in killerwhales, 185; in magpies, 186; in NewCaledonian crows, 186

196 INDEX

Cuticle, 44, 112, 127, 150, 160Cystic fibrosis, 40

Daydreaming, 174Dehalococcoides ethenogenes, 8Dentine, 118–119Dermochelys coriacea, 13–14Devil’s Garden Ant, 16–18Diaphysis, 85Diatom, 66, 131–133Dispersal, by parasites, 42, 70–72DNA, 11, 21, 29–32, 40–42, 52–53, 72,182–184, 187–190

DNA, fiber optics, 190DNA-polymerase, 30–31DNA replication, 30, 188Domatia, 18Domestication of animals, 55–56Dorsal hump, 94Double helix, of DNA, 188, 189Dragonfly larva, 163–164Dreaming, 174Drilling, 95Duck-billed platypus, 21, 147–149Duroia hirsuta, 17

Ear drum, disconnection of in bats, 146Echolocation, 117, 144–147Ectothermy, 12–14Electric eel, 19–21, 147Electricity, 2, 10, 19–21, 34, 81, 139,147, 170, 190

Electro-spinning, 135Electrocyte, 19–21Electrophorus electricus, 19Electroplaque, 19Electroreceptor, 20ElectrosenseEleutherobin, 127Enamel, 118–119Endosymbiotic theory, 5, 10Endothermy, 12–14Energy, 1–13, 15, 17, 19–23, 37, 40–42,48–50, 59–60, 63, 65–68, 70, 73, 76, 79,84, 89, 91, 93, 97, 105–105, 112, 115,126–128, 130, 148, 156, 172, 179, 181

Enzyme, 11–12, 15, 28–31, 41, 44, 53, 183Epidermis, 89, 92

Epiphysis, 85Epitheca, 132EpsE protein, bacterial clutch, 77Eptatretus stoutii, 96Ethyl glucuronide, 35Eumelanin, 34Eusocial organisms, 129–130Evolutionary arms race, 113, 146Exploration, arctic, 26–27Exoskeleton, 87Eye: artificial, 142; compound, 88, 142–144, 166; human, 141; insect, 142–144; of mantis shrimp, 165–167;specialized, 141, 162–165; vertebrate,140–142, 152

Fat, 11, 14, 29, 32–33, 40, 85Fat innkeeper, 197Fatal familiar insomnia, 52Feather, 59, 89–91, 116–117Fertilizer, chemical, 38Fire, use by humans, 1Fire fighting, 16, 151Fire beetle, 149–152Fire extinguisher, 16Flea, 103–105Flight, human machines for, 56–57Flight, in birds, 58–60, 90Flight, in insects, 60–63, 162Follicle, 33, 89, 93Formic acid, 17–19Fovea, 141FOXP2 gene, 176Frontal cortex, 173Frontal lobe, 176Frustule, 132–133Fuel-injection system, 16Fungi, 22, 45–46, 48–49, 83, 96, 112–113, 121

Fur, animal, 25, 33–35; of pen-tailed treeshrew, 34–35; of polar bear, 33–35, 47

Gecko feet, 100–103Gecko tape, 103Gecko-bots, 103Gene, 24, 29, 31, 32, 38, 130, 131, 134,155–157, 176, 180, 182–184, 187–189;evolution of, 189

INDEX 197

Gills, 39, 67, 88, 96Glial cell, 172Glow sticks, 24Glucose, 1, 3–4, 35Glue, 40, 74, 98–100, 102, 124, 134; inmedicine, 100; underwater, 99–100

Guided missile, 147, 151

HACNS1 gene, 189Hagfish, 96–98Haltere, 62–63, 162Haplodiploidy, 130Haversian canal, 85–86Heat-seeking missile, 151Heating, in human dwellings, 112, 119Hemoglobin, 25, 44, 131Herbivory, 17–18, 116, 179–180Heterocephalus glaber, 128–131HIV, treatment of, 127Hive, bee, 120–121, 176, 180–182Hormone: plant, 178–179; sex, 130, 154,161

Hormone receptor, in plants, 178Human mating behavior, 155–157Hummingbird, 58–60Hunter gatherer humans, 19, 55, 93,107, 187

Hunter’s organ, 19–20Hydrodynamics, 67Hydrogel, 115Hydrogen peroxide, 15Hydrogen pump, 4Hydroquinone, 15Hydrothermal vents, 6–7, 29–30Hydroxyapatite, 84, 86, 95Hypotheca, 132Hypoxia, treatment of, 131

ICAM-1 receptor, 71Ice worm, 47–49Inbreeding, 130, 157Inflammatory mediators, 71Infrared detection, by humans, 138, 151,153

Infrared detection, fire beetle, 149–151Infrared vision, in snakes, 151–153Inhaler, 16Inner dermis, 92

Insect repellent, 162Insulation, 14, 26, 33–35, 89–90, 119,121, 123

Internal combustion engine, 56Internet, 171Involucrum, 121Ion pump, 4, 19, 20, 37, 76Iron, use by humans, 80–82

Jacobson’s organ, 153–155Jet engine, 56–57Jet propulsion, 68–70Jewel beetle, 149–152Junk DNA, 32, 189

Keratin, 33, 87, 89, 91–92Kin recognition, 126, 155–157,178–179

Knife fish, 19

Lamellae, in bone, 85Land, colonization from water, 38–39Language, bee, 180–182Language, human, 174–177Leaf-cutter ant, 47Leatherback turtle, 13–14Lens, eye, 88, 140–141, 143, 166Lens, glass, 137–138Lenticel, 38Leucochloridium paradoxum, 71Lift, in flight, 56–62, 68, 90, 133Lignification, 113Lock-and-key hypothesis of enzymeaction, 30, 53

Loosejaw dragonfish, 21–23Luciferase, 22, 24, 127–128Luciferin, 22, 24, 127–128Luminous gnat, 127–128Lung, 38–40, 43, 60, 64–65, 175–176Lungfish, 38–40

Macrotermes, 109–112Magnetic field: germination in, 159;navigation with, 147–149, 158–160

Magnetic sense, 158–160Magnetite, 158Magnetosome, 158Main organ, 19

198 INDEX

Major Histocompatibility Complex(MHC), 155–157

Malacosteidae, 22Malaria, prevention, 19Mangrove, 35–38Mantle, mollusk, 69, 94Marine salp, 69–70Mechano-sensor, 149Medicine, 24, 45, 47, 81, 89–90, 93–94,98, 105, 127, 162

Melanin, 34, 40–42, 90–91; black(eumelanin), 41; red (phaeomelanin),41

Melanocyte, 40–42Memory, 19, 167, 173–174, 181, 184,189

Mesenchytraeus solifugus, 47Metabolism, 8–12, 33, 35, 48, 51, 67, 96Metapleural gland, 45–47Metapleurins, 45–47Methylococcaceae, 7Micro Air Vehicle, 63Micro-robots, 77, 103, 133, 142Microbial fuel cell, 21Microphone, 139, 170–171Microscope: electron, 138; light, 137Microscopic sieve, 133Microvilli, in olfactory nerves, 155Midband, of mantis shrimp eye, 166–167Migration, human, 25, 55Mimicry, 23Miracidia, 71Mitochondria, 9–10, 25, 158Mollusk, 69, 94–95Moral behavior, 186MRSA, 183–184Mucus, 8, 39–40, 71, 96–98, 127–128,149

Muscle, 14, 19–20, 25, 27–28, 34, 59–61,63–69, 72, 76, 85, 88, 92, 98, 100, 104,121, 123, 124, 140, 141, 146, 164, 166,167

Mutation, 17, 3253, 188Mutualism, 17–18Myrmelachista schumanni, 17Myxini, 96

Naked mole rat, 128–131, 158–159

Nano-particles, 190Nanotechnology, 77, 86, 133, 190Navigation, 21, 159, 182Nectar, 34, 60, 73–74, 151, 161, 180–81Needle-free injection, 16Nekton, 66Nerves, 19–20, 34, 63, 72, 92, 131, 140–143, 147–150, 152–155, 158–161,171–174, 178, 189

Neural network, 174Nitrosomonas, 7Nose: artificial, 98, 140, 155, 157; dog,97, 98

Noseleaves, in bats, 145Notothenoids, 31–32

Ommatidia, 142–143, 166Onychophora, 99Opposable thumb, evolution of, 189Optics, biological, 91, 190Orchid, 73–75Organelle, 5, 9, 138, 158, 178Ornithorhynchus anatinus, 147–149Osmosis, 35Osteoblast, 85–86Oxygen poisoning, 11, 44

Pachystomias microdon, 22Paper nest, 122–124Paper wasp, 122–124Parallel navigation, 146Parasitism, 42–44, 70–72Parietal cortex, 173Parkinson’s disease, 54PEG region of brain, 173Penguin, 90, 115Penicillin, 45Periosteum, 85Persian wind tower, 112Phaeomelanin, 34Pharmaceuticals, 45, 47Pheromones, 161Phloem, 112–115Photinus, 23Photonic crystals, 91Photophore, 23Photosynthesis, 3–6, 37, 113, 126Photuris, 23

INDEX 199

Pit organ, 152–153Pit viper, 151–153Plankton, 22, 66Plant distress call, 179–180Plasmid, 11, 182–184Plastics, 11, 26, 34, 39, 80–81, 103Plastron, in insect eggs, 88Pleural arch, 103–104Pneumatophore, 38Poison, 15, 18, 23, 34, 77, 116, 179,187

Poisoning, oxygen, 11, 44Poisoning, salt, 35–38Polarized light vision, 167Polistinae, 123Pollination, 72–75Polybutadiene, 105Polymers, 26, 80–81, 87–88, 113, 124Pore kettle, 160Portia spider, 164–165Power stations, 2Printing, 170Prion, 51–54Problem solving, 164–165, 173–174,177

Proline, 105Propeller, 57, 68, 75–76Propolis, 120–122Protease, 53Protein, 11, 19–20, 28–33, 40, 44, 52–54,76–77, 82–84, 87, 89, 91–92, 94, 96,99–100, 104–105, 126–127, 133, 155,159, 183, 188

Protein structure, 53Protopterus annectens, 38–40Prototaxites, 113Pseudomonad bacteria, 11Pseudoscorpion, 83Psittacofulvins, 99Psychrophile, 47–49Ptilonorhynchidae, 117Pyramids, 107–108Pyrolobus fumarii, 30

Queen, in hymenoptera, 18, 46, 109,121–122

R-plasmid, 183

Rabies virus, 72Rachis, 89–90Radiation, 5, 25–26, 28, 40–42, 51, 53,138, 150–152

Radula, 94–95Reporter gene, 189Resilin, 103–105Respiration: aerobic, 10–11, 21;anaerobic, 65, 67

Retina, 140–143, 159Retina, ramp, 141Rhinovirus, 70–71Rhodococcus, 11Rhizophoraceae, 35Robotics, 77, 103, 133, 139, 142, 149,155, 157, 165, 182

Rod, photoreceptor, 140–141, 166Roundworm, 43–44Running: in alligators, 64; in thecheetah, 64–66; in lizards, 63–64; inmammals, 63–66

Sach’s organ, 19–20Salt gland, 37Salt poisoning, 35–38Sarcopterygii, 39Scytodidae, 98Secondary growth, 113–114Semiconductors, 2Sensillum, 160Sensory cortex, 172–173Sequoia, 113–114Setae, in Gecko feet, 101–103Sex pilus, in bacteria, 183Shark, 84, 93, 148–149, 158Shelter, human, 26,Side-blotched lizard, 13Sight, 20, 22, 137, 141, 145, 163–167Silaffins, 133Silica deposition vesicle, 132Silk, 82–84, 98, 124, 127–128, 134–135,161

Siphon, squid, 69Skin, 65, 91–94, 139–140Skyscrapers, 81, 98, 107–108Slot effect, 59–60Smell, 88, 97–98, 100, 140, 153–158,160–162, 180

200 INDEX

Smell detector, artificial, 98, 140, 155,157

Smoke detector, 149–151Solar panels, 2, 5–6Solvent, 99Space station, providing oxygen in,27

Space travel, 28, 49, 51, 59, 159–160Space-filling gel, 98Spatulae, in Gecko feet, 101–102Speckled-wood butterfly, 13Spiders, 8, 82–83, 98–99, 128, 134–135,164–165

Spitting spider, 98Spoon worm, 91Sporocyst, 72Squid, 22–23, 69–70, 94, 141Stalling, in flight, 59, 62Stem-cell research, 24Stomata, 112Strain 121, 30Submarine, 27, 57Sunscreen, 28, 41–42Super-sense, 172–173Supercoiliing, 30, 188Surfacant, 40Surgical suture, 84, 89, 100Swarming, 161Sweating, 26, 49, 65, 72, 93Swimming, 66–68Symbiosis, 49, 126, 162

Tardigrade, 49–51Tardigrade, tun formation, 51TARDIS, Tardigrades in space, 51Taste, 88, 159, 153–154, 160–161, 172,180

Telescope, 138Telescope, radio, 138Television, 171Temporal lobe, 176Termite mound, 109–112, 186Termitomyces, 111Thaliacea, 69Thiobacillus, 7–8Thrust, in locomotion, 57–61, 66–68,70, 75, 90

Thunnus thynnus, 66

Tiger snake, 154–155Tool use, 25–26, 55, 79–80, 186Tool use: in chimpanzees, 185–186; inNew Caledonian crows, 186

Torpor, 39, 50–51, 96Touch sensor, artificial, 139Transmissible Spongiform Encephalitis,52–54

Transpiration, 114–115Tree, artificial, 115Trees, 17–18, 35–38, 112–115, 116,178–180

Trehalose, 49–51Triple-helix, protein, 44Trophosome, 7Tube worm, 6–7Tumbling, in bacteria, 76–77Tunicate, 69

Ultrafast internal conversion of energy,41–42

Urechis caupo, 97–98Ursus maritimus, 33–34U.S. Department of Energy BerkeleyLaboratory, 6

van der Waals force, 101–103Vehicle: man-made, 55–58; unmanned,57, 63, 66, 144

Velvet worm, 99Venom, 15, 128Ventilation, 112, 119, 121–122Vescomyidae, 7Vestimentifera, 6–7Viral replication, 71Virus, 42, 52, 70–72, 96, 138, 184Vision, 141–144, 151–153Vision: infrared, 151–153; ultraviolet,91, 162–167

Visual aids, 142, 147Vocal cords, 175Voice box, 175Vomeronasal organ, 153–155, 157von Frisch, Karl, 180Vortex, 61–62

Waggle dance, in bees, 180–181Warmblooded animals, 12–13, 33

INDEX 201

Wasp nest, 122–124Water bear, 49–51Watson, James, 187–188Wax, 37, 89, 112, 120–122Weaver bird, 115–117Web, communal, 135Web, spider, 8, 83, 134–135Wing: bird, 58–60, 89–90; bat, 145–146;

insect, 15, 60–63, 73, 87–88, 103–104,122–123, 162, 181

Writing, 169–170

Xylem, 113–114

Zooxanthellae, symbiotic relationshipwith coral, 126

202 INDEX

About the Author

ADAM SIMMONS has broad experience in the field of biology—specializingin evolution, ecology, and animal behavior. He has published his own researchin Nature, American Naturalist, and Animal Behaviour. He holds a PhD fromthe University of Leeds, where his thesis set out, tested, and supported a novelhypothesis about the evolution of dispersal traits and behavior during speciesrange expansions and invasions, which revealed important implicationsfor the impact of climate change. He has taught biology to students of manylevels, from kindergarten to undergraduates. He currently works for theU.K. civil service, and in his spare time he is a keen natural historian andfollows his interests in languages and sport.

Encyclopedia of Adaptations in Natural World

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