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EVOLUTION AND GENETICS

EVOLUTION AND GENETICS

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Evolution andGenetics

Contents PHOTOGRAPH ON PAGE 1In vitro fertilization. The imageshows the moment at which thesperm DNA is injected into an ovule.

Myths andScientificEvidence

Page 38

HumanEvolution

Page 68

The Age ofGenetics

Page 54

Mechanisms ofHeredity

Page 18

Origin of Life

of the answers that people have foundthroughout history, through their successes,failures, and new questions. These newquestions have served to shape the world inwhich we live, a world whose scientific,technological, artistic, and industrialdevelopment surprises and at timesfrightens us. History is full of leaps. Forthousands of years nothing may happen,until all of a sudden some new turn ordiscovery gives an impulse to humankind.For example, with the domestication ofanimals and the cultivation of plants, aprofound societal revolution occurred. Thisperiod of prehistory, called the Neolithic,which dates to 10 million years ago, openedthe way for the development of civilization.With the possibility of obtaining foodwithout moving from place to place, the firstvillages were established and producedgreat demographic growth.

The book that you have in yourhands explains all this in anaccessible way. Here you will

also find information about the latestdiscoveries related to the structure ofDNA, the molecule of heredity, thatopens new areas of investigation. Itcontributes to the study of clinicaland forensic medicine and positsnew questions about the origin oflife and where we are headed ashumans. The possibility ofuntangling the sequence of thehuman genome is not only important intrying to explain why we are here and toexplore our evolutionary past, but it alsooffers the possibility of altering ourfuture. In the decades to come, theapplication of genetic therapy will allow,among other things, the cure of geneticdisorders caused by defective genes. Inaddition, the alternative of knowing

FACES OF THE PASTThe skull of Australopithecus (below)shows a reduced cerebral portion and astrong jaw. To the right, Cro-Magnon, arepresentative of modern humans,exhibits a more evolved skull withgreater cerebral capacity.

beforehand what diseases a person coulddevelop will be extremely valuable in thefield of health, because we will be able tochoose examinations and treatmentsaccording to individual needs. Another verypromising area of medical research involvesthe use of stem cells that have the uniquecapacity to be used at some future date toregenerate organs or damaged tissues. Do not wait any longer. Turn the page andbegin to enjoy this book, which may be apoint of departure in your own adventure in learning.

When did humans appear? What is itthat makes us different from therest of the animals? In what way

did language develop? Why is it soimportant to have deciphered the sequenceof the human genome? This book offersanswers to these and many other questionsabout the mysteries and marvels of humanevolution. Scientists maintain that modernhumans originated in Africa because that iswhere they have found the oldest bones. Inaddition, genetics has just arrived at the

same conclusion, since the DNA studieshave confirmed that all humans arerelated to the African hunter-gathererswho lived some 150 million years ago.

Studying the fossils, the experts alsofound that human skulls from two

million years ago already show thedevelopment of two specificprotuberances that in thepresent-day brain control speech,the capability that perhaps wasas important for early humans as

the ability to sharpen a rock or throwa spear. Today thanks to science it is

possible to affirm that the brain haschanged drastically in the evolutionary

course of the species, reaching a greatercomplexity in humans. This has facilitated,among other things, the capacity to storeinformation and the flexibility in behaviorthat makes a human an incredibly complexindividual. The purpose of this book is to tellyou and show you in marvelous images many

Yesterday,Today, andTomorrow

Myths and Scientific Evidence

elements. It represents not simply anunlimited number of genetic mutationsbut also changes in the environment,fluctuations in sea level, varyingcontributions of nutrients, and possibly

factors such as the reversal of theEarth's magnetic field or the impact oflarge meteorites on the Earth's surface.In this chapter, we tell you stories andlegends from some of the most remote

places in the world as well as variousscientific theories concerning the originof life and of human beings. Some of thecurious facts and photos in these pageswill surprise you.

VARIOUS BELIEFS 8-9

EVOLUTION IS A MATTER OF TIME 10-11

EVOLUTIONARY PROCESSES 12-13

TO LIVE OR DIE 14-15

THE CRITICAL POINT 16-17

BLACK SHEEPThe black color of thisspecimen is a clearexpression of genes, thefunction of which is todetermine different traits.

The evolution of species cannotbe considered an isolated eventin itself but rather the result of acomplex and constantinteraction among different

EVOLUTION AND GENETICS 98 MYTHS AND SCIENTIFIC EVIDENCE

Various BeliefsB

efore the emergence of scientific theories, most people inthe world had their own versions of the origin of theworld and of humankind expressed primarily in the form

of myths. Many of them have reached us through the teachingsof different religions. In many cases, the origin of the world andof humankind relates to one or several creator gods or demigods;in other cases, there is no beginning and no end. With regard to theorigin of the human race (the word “human” shares the same rootas the Latin word humus, meaning “earth”), there is a CentralAfrican legend that links humans to monkeys.

Africa: How Monkeys Became HumanIn Africa, the continent that is today believed to be the cradle of the humanspecies, there are several myths that account for the origin of mankind. One of

these actually interweaves it with the origin of the monkey. It tells how the creator godMuluku made two holes in the Earth from where the first woman and the first mansprouted and how he taught them the art of agriculture, but they neglected it and theEarth dried up. As punishment, Muluku banished them to the rainforest and gave themmonkey tails, and he removed the tails from monkeys and ordered them to be “human.”

DisobedientJudaism, Islam, and the various forms ofChristianity adhere to the book of Genesis in the

Bible, according to which the world was created by God inseven days. According to this account, the first human wascreated on the sixth day “in the image and likeness” of theCreator. The intention was for this new creature to

rule over nature. The first woman, Eve, emerged from oneof Adam's ribs. Because they disobeyed the Creator by

eating one of the forbidden fruits, Adam and Eve werebanished from Paradise. Condemned to work the soil and for

woman to suffer during childbirth, they had three sons,from whom the human race descended.

other cultures, life is also identified with thebreath of the creator of the world. In Egyptianmythology, for example, the breath of the god Ra,“The Limitless God,” transforms into air (Shu),which is the indispensable element of life.

The Divine BreathThe story explains that God gave life toinert matter through either breath, as

shown in the image above, or touch, as shown inthis fragment of the Final Judgment, painted ona chapel ceiling in the Vatican in 1541. In many

The Matter of Creation

India is a multicultural,agricultural society where much

of its thousand-year-old rituals stillexist. However, its sacred texts werewritten at very different times, from1,000 BC (the Rigveda) to the 16thcentury AD (the Puranas), and theyoffer different versions of theorigin of humankind. One ofthem even tells of a primalman (Purusha) from whomgods originated and fromwhose body parts the differentcastes arose. In this culture,social classes are stronglydifferentiated.

FORBIDDENFRUIT

According to thebiblical account, Adam

and Eve ate the fruit ofthe Tree of Knowledge ofGood and Evil.

EDENThe biblical story locates theearthly Paradise inMesopotamia. In Paradise, allthe living species lived, andhumans had only to take what they needed.

BRAHMA,THE CREATORAnother version states thatthe first human emergeddirectly from the godBrahma, whose human imageis represented by this statue.

HERMAPHRODITEAccording to more recenttexts (from the 15th century),the first person Brahmacreated was called Manu, andhe was a hermaphrodite. Thestory goes that as a result ofhis dual sexual condition, hehad a number of children,both males and females.

PROPORTIONThe size of theheads revealsthe importancegiven to thesymbols.

YORUBAMASKrepresentsthe twosexes.

THE TWO SEXESAlthough Genesis is somewhatcontradictory on this point, thedominant version states thatGod created Eve from one of

Adam's ribs while he slept.That is what the

Nuremberg Bibleillustrates.

HUMAN SHAPESChristianity representedthe Creator and the angelsin human form, butJudaism and Islam did notassign a human likeness totheir God.

CREATIONThe work of Michelangelois found in the SistineChapel in the Vatican.

DinosaursAnimals that livedmillions of years agoleft behind their fossilremains. Sediment

Sediment from rivers and seasis deposited over the skeletonand forms into layers.

DiscoveryErosion on the Earth'ssurface leads to thediscovery of fossil remainsfrom millions of years ago.

Fossil RemainsThe evidence of past life is registered infossils, preserved between layers ofsedimentary rocks deposited one on top ofanother through geological eras. An analysisof fossils helps determine their age. Throughstudies of fossil populations, it is possible tolearn about the structure of old communities,the reason given species becameextinct, and how animals andplants evolved over time.

A

millionyears150is the typical age ofdinosaur fossils.

extinctspecies.

20,000


CarpalKEY

In mammals, the basic design ofthe limb is very similar—an upperbone (humerus), followed by apair of lower ones (radius andulna), and then the carpalsand metacarpals withup to five digits.

A Common HistoryAnimals that look very different may bebuilt according to the same basic bodydesign. For example, dogs, whales, andhuman beings are mammals. All have thesame skeletal design with a spinal column

and two pairs of limbs connected to it. Thissuggests that they all share a commonancestor. In mammals, the bones of thelimbs are the same even if they aremorphologically different from one another.

BATWHALE

CAT

HUMAN

PETRIFIED FOSSILSThis head of anAlbertosaurus discoveredas a fossil can be studiedusing geological orbiomolecular analyses.

Evolution Is aMatter of Time T

oward the 18th century, scientific progressdemanded a different explanation of the myth ofthe origin of the world and of life. Even before

Darwin, the work of naturalists and the discovery offossils pointed to the fact that time, measured not inyears but in millennia, runs its course, allowing eachspecies to become what it is. Genetic mutations occurthrough the generations, and interaction with theenvironment determines that the most suitable traits willbe transmitted (natural selection) and that a populationwill evolve in relationship to its ancestors. The idea is notrelated to “improvement” but rather to change as theorigin of diversity, to the ramifications of evolutionarylines tracked through paleontological or genetic studies.

Humerus Radius

Genetics With the use of advanced biomolecular techniques,it is possible to examine the evolutionary legacy of aspecies and figure out when evolutionary linesdiverged. Many anthropologists use mitochondrialDNA (which is inherited from the mother) toreconstruct human evolution. This type of analysis isalso used to reconstruct the family trees of animals.

B

BurialBacteria and otherunderground organisms canmodify the buried skeleton.

Only one fossil isfound for every

1

2

3

4

MetacarpalUlna


Evolutionary ProcessesI

n addition to natural selection, the famous theory developed byCharles Darwin in the 19th century, there are other evolutionaryprocesses at work at the microevolutionary scale, such as

mutations, genetic flow (i.e., migration), and genetic drift. However,for evolutionary processes to take place, there must be geneticvariation—i.e., modifications to the proportion of certain genes(alleles) within a given population over time. These geneticdifferences can be passed on to subsequent generations,thereby perpetuating the evolutionary process.

Natural SelectionThis is one of the basic mechanisms of evolution. It is theprocess of species survival and adaptation to changes in theenvironment, and it involves shedding some traits andstrengthening others. This revolutionary transformationtakes place when individuals with certain traits have asurvival or reproduction rate higher than that of otherindividuals within the same population, thus passing alongthese genetic traits to their descendants.

A

Mutationinvolves the modification of the sequencesof genetic material found in DNA. When acell divides, it produces a copy of its DNA;however, this copy is sometimes imperfect.This change can occur spontaneously, suchas from an error in DNA replication(meiosis) or through exposure to radiationor chemical substances.

B

Genetic FlowThe transfer of genes from one populationto another occurs particularly when twopopulations share alleles (different versionsof genes). For example, when a populationof brown beetles mixes with a populationof green beetles, there might be a higherfrequency of brown beetle genes in thegreen beetles. This also occurs when newalleles combine as a result of mixing, aswhen Europeans mixed with NativeAmericans.

C

Genetic DriftA gradual change in the genetic makeup of apopulation that is not linked to theenvironment. Unlike natural selection, this isa random process that does not generateadaptations. Genetic drift is present in smallpopulations in which each individual carrieswithin itself a large portion of the geneticpool, especially when a new colony isestablished (the founding effect), or when ahigh number of individuals die and thepopulation rebuilds from a smaller geneticpool than before (the bottleneck effect).

D

COMPETITIONIn the 19th century, becauseof the theories of Darwin andLamarck, among others, itwas believed that theancestors of giraffes hadshort necks.

1

MUTATION On the basis ofspontaneous mutations,some individuals developedlonger necks, allowingthem to survive in thecompetition for food.

GENETIC VARIATIONIN THE GIRAFFE

THE GEOMETRIC MOTH AND ITS ENVIRONMENTThe genes of geometric moths, which liveon tree bark lichen, have differentversions (alleles) for gray and black. Atthe start of the Industrial Revolution inEngland, the gray moth was better able tocamouflage itself than the black moth andthus better able to avoid predators. Allthis changed with the emergence ofpollution, which blackened tree trunks.

2

ADAPTATIONTheir long necksallowed them tosurvive and passalong this trait totheir descendants.

3

MIMESISThe population of mothswith gray alleles growslarger because of itscamouflage.

1

POLLUTIONMoths with black alleles findthemselves better adapted totheir new environment, which isthe result of industrial pollution.

2

THE PROPORTION OFBLACK MOTHS FOUND INURBAN AREAS

DREPANA FALCATARIAwas found hidden on a treein Norfolk (U.K.) in 1994.

95%

SURVIVALThe population of mothswith black alleles grows andsurpasses the populationwith gray alleles.

3

THE PROCESS A mutation is adiscrepancy inthe DNA copy.

COPY WITHMUTATION

CORRECTCOPY


To Live or DieC

oevolution is a concept used by scientists to describe theevolutionary process from a group perspective, because no singlespecies has done it in isolation. On the contrary, different levels

and types of relationships were established through time betweenspecies, exerting changing pressures on their respective evolutionarypaths. Natural selection and adaptation, both processes that everyspecies has undergone to the present, depend on these relationships.

Mutualismis a type of interspecific relationship in which bothspecies derive benefit. It might seem as if this isan agreement between parties, but it isactually the result of a long and complicatedprocess of evolution and adaptation. Thereare numerous examples of mutualism,although the most famous is the cattleegrets of Africa (Bubulcus ibis), whichfeed on the parasites of large herbivoressuch as the buffalo and the gnu. To theextent that the egrets obtain their food,the herbivores are rid of parasites.

B

Commensalismis a relationship between two speciesof organisms in which one benefits andthe other is neither harmed nor helped.There are several types ofcommensalism: phoresy, when onespecies attaches itself to anotherfor transportation; inquilinism,when one species is housedinside another; andmetabiosis, such as whenthe hermit crab lives insidethe shell of a dead snail.

ATypes of RelationshipsIf the evolution of each species were anisolated event, neither the relationships nor

the adaptations that together generate coevolutionwould exist. In fact, in the struggle for survival,some species react to the evolutionary changes ofother species. In the case of a predator, if its preywere to become faster, the hunt would become moredifficult and a demographic imbalance woulddevelop in favor of the prey. Therefore, the speed ofeach depends on the mutual pressure predator andprey exert on each other. In nature, different typesof relationships exist that are not always clear oreasily discernible given the complexity they canacquire through the process of coevolution. Theserange from noninteraction to predation, fromcooperation to competition and even parasitism.

Competitiontakes place when two or more organisms obtain theirresources from a limited source. This is a relationship thathas one of the strongest impacts on natural selection and theevolutionary process. There are two types of competition.One occurs through interference, which is when an actionlimits another species' access to a resource—for example,when the roots of a plant prevent another plant fromreaching nutrients. The other type of competition is throughexploitation, typical among predators such as lions andcheetahs that prey on the same species. In this second type,the principle of competitive exclusion is also at play, sinceeach species tends to eliminate its competition.

D

DebateFOR EVOLUTIONARY SCIENTISTS, IT IS NOT CLEARWHETHER THE DRIVING FORCE OF EVOLUTION IS

COOPERATION OR COMPETITION. THE LATTERNOTION HAS BEEN FAVORED BY THE SCIENTIFIC

COMMUNITY SINCE THE 19TH CENTURY.

COMPETITIONThere is alsocompetitionwithin a species,whether for foodor for matingpartners.

Predationis the interspecies relationship in which one species huntsand feeds on another. It is important to understand thateach party exerts pressure on and regulates the other.There are specific instances of predation in which thehunter impacts only one type of prey or those in which itfeeds on different species. The degree of adaptationdepends on this distinction. The lion, the zebra, and thekudu form an example of the latter case.

E

Parasitismis defined as an asymmetricrelationship in which only one ofthe organisms (the parasite)derives benefit. It is an extremecase of predation that entailssuch fundamental adaptationswhere the parasite, which entersby various means, might evenlive inside its host. Such is the

case of the African buffalo,which can have a worm

called Elaeophora poelilodged in its aorta.

C

TheEnvironment

INTERACTS WITH COEVOLUTION,SUCH AS WHEN AN

ENVIRONMENTAL CHANGE FAVORSOR HARMS A GIVEN SPECIES.


The Critical PointO

ne of the big issues posed by the theory ofevolution is how a new species arises. Thispresumes that a population becomes separated

from other individuals within its group (when, forexample, it lives under conditions different from thoseof its parents) and ceases to interact with them.Through the generations, the isolated individuals willexperience genetic mutations that give rise tophenotypic changes completely different from thoseexperienced by the original population to which they oncebelonged, and they develop traits so distinct that theybecome a new species. From an evolutionary perspective,this is how one can understand the constant emergence ofnew lineages and the growing diversity of living beings.

The origin of new species

SelectionIn spite of their differences, dogs are so similar toeach other that they can breed with each other.They are in the same species. But selectivebreeding is a good example of how differentiationis favored, except that in nature it takes a longertime to do this. Selection can be disruptive, whentwo populations separate and becomedifferentiated; directional, when the dominanttraits of a population change; or stabilizing, whenvariations diminish and individuals become moresimilar to each other.

THE HONEYCREEPERSNew species can arise from a commonancestor. All the Hawaiian honeycreepersevolved from the same ancestor. Theyhave different colors and bills.The original species is now extinct. The diet of the honeycreeperchanged with each new generation.

Gray WolfCanis lupus

Individuals of the same species look alikeand breed among themselves, but not

with those of other species. In speciation, twoor more species arise from a single species(cladogenesis), or several fertile individualsarise from the crossbreeding of two different

species (hybridization), although the latter ismuch less frequent in nature. Cladogenesis canarise out of geographical isolation or simplythrough a lack of genetic flow between groupsof individuals of the same species, even if theyare present in the same territory.

Their varying shapes explainthe adaptation of each bird tothe changes in its diet.

Bills

Siberian HuskyCanis familiarisUnlike the German shepherd,which evolved through 10,000years of human-breeding, theSiberian husky preserves traitscloser to those of the gray wolf,which are the ancestors all dogs.

German ShepherdCanis familiaris

The ancestor of the dogis very intelligent andsocial. It travels in packsof 8 to 12 members.

This strong, trainabledog herds cattle andsheep tirelessly andwith great intelligence.

ApananeHimatione sanguineafeeds on insects andohia flower nectar.

Akiapola'auHemignathus munroisearches for insects under-neath the barks of trees.

IiwiVestiaria coccineafeeds exclusively on nectar.

Maui ParrotbillPseudonestor xanthophrysremoves bark in searchof beetles.

Nihoa FinchTelespiza ultimacan shatter seedswith its hard beak.

Hawaii AmakihiHemignathus virenshas a curved bill andfeeds on nectar.

THE REIGN OF THE DINOSAURS 30-31

THE END OF THE DINOSAURS 32-33

LAND OF MAMMALS 34-35

THE TREE OF LIFE 36-37

Origin of Life

An effort of imagination isneeded to see just how newcomplex life-forms are onEarth. For millions of yearsthe development of life was

completely static. Suddenly one day thisstagnant world exploded unexpectedlywith new forms of life, an effect calledthe Cambrian explosion. The fossilrecord shows an impressive proliferation

of incredibly varied life-forms. Theemergence of new species in the oceanstook place at the same time as themassive extinction of stromatolites,which had dominated the Proterozoic

Eon up to that point. In this chapter youwill also discover how new creaturescontinued to appear that over timepopulated the face of the Earth.

THROUGH TIME 20-21

CHEMICAL PROCESSES 22-23

FOSSIL RELICS 24-25

THE CAMBRIAN EXPLOSION 26-27

CONQUEST OF THE EARTH 28-29

PREHISTORIC ANIMALSRe-creation of Titanis (a fiercebird) and of the horse Hipparion,two primitive animals that livedduring the Cretaceous Period

EVOLUTION AND GENETICS 2120 ORIGIN OF LIFE

Geologic structures and fossils have been used by scientists to reconstruct the history of life on ourplanet. Scientists believe that the Earth was formed about 4.6 billion years ago and that the firstliving beings, single-celled organisms, appeared about one billion years later. From that time, the Earth

has registered the emergence, evolution, and extinction of numerous species. Thanks to the study of fossilspaleontologists can provide an account of plants and animals that have disappeared from the Earth.

Through Time

HOW IT STARTEDFORMATION OF THE CRUST. Theoldest known rocks date to about fourbillion years ago and the oldest knowncrystals to about 4.4 billion years ago.

THE TIMELINEMost of the history of life on the planethas had simple, single-celled organisms,such as bacteria, as the lead actors.Bacteria have survived for more thanthree billion years. In comparison, thereign of dinosaurs during the Mesozoic Era(about 250 to 65 million years ago) is arecent event. And the presence of humanson Earth is insignificant on this time scale.

ANAEROBIC AND AQUATIC LIFE.The first atmosphere had no oxygen;the first organisms (bacteria) usedanaerobic respiration.

A CURIOUS FOSSIL. This fossil inmawsonite found in the Ediacara ofAustralia is one of the oldest fossilsfrom a metazoan, or multicellular,animal. It is at least 600 million yearsold. Cnidarians are well-representedamong Ediacaran fossils.

THE FIRST EVIDENCE.Stromatolites, fossils that dateback some 3.5 billion years, areone of the first evidences of lifeon the planet. These formationscorrespond to single-celled algaethat lived underwater. In this imageyou can see a fossil of Collenia, foundin the United States.

PRESENCE OF OXYGEN. Life on Earth wasdependent on the presence of oxygen, whichestablished itself in the atmosphere and overthe surface some 2.1 billion years ago. Oxygen

makes possible the formation offundamental compounds, such as water

and carbon dioxide, whose molecularmodel is shown here.

PROTECTED LIFE. The mostcommon animal life-forms ofthe Cambrian Period alreadyshowed well-defined bodystructures. Many wereprotected by valves or shells.

CONQUEST OF EARTH.The first land species appearedduring the Silurian Period. Plantsinvaded the first sedimentaryareas, and crustaceans came out of the water.

MASSIVE EXTINCTIONS.Great climatic changes andother circumstances producedthe first massive extinctions ofspecies, evidenced by greatbanks of fossils.

THE ERA OFREPTILES. Large andsmall, they conqueredterrestrialenvironments, butthere were also aquaticspecies (such as theIcthyosaurus) andothers in the air (suchas the Pterosaurus).

NEW TYPES OFANIMALS. The firstmammals and birdsappear on Earth. Therewas a greatdiversification ofmollusks in the oceans,where species such asthe nautilus survive tothis day.

A CHANGINGWORLD. The end ofthe Mesozoic Erawitnessed a greatclimatic change witha major fall in averagetemperatures. This ledto an era ofglaciations.

4.6 BILLIONYEARS AGO.The basicmaterials thatformed the Earthcondensed.

1 BILLION YEARSAGO.Several largecontinental piecescome together,forming thesupercontinentRodinia.

PRECAMBRIAN TIME

ARCHEAN EON

4.6-2.5 BILLION YEARS AGO 2.5 BILLION-542 MILLION YEARS AGO 542 - 488 488 - 444 444 - 416 416 - 359 359 - 299 299 - 251 251 - 200 200 - 146 146 - 65.5 65.5 - 23 SINCE 23 MILLION YEARS AGO

PROTEROZOIC EON CAMBRIAN ORDOVICIAN SILURIAN DEVONIAN CARBONIFEROUS PERMIAN TRIASSIC JURASSIC CRETACEOUS PALEOGENE NEOGENE

PALEOZOIC ERA MESOZOIC ERA CENOZOIC ERA

270 MILLIONYEARS AGO.The mass of solidland is againconcentrated in asingle continent,called Pangea,that would

become the originof the continentswe know today.Repeatedglaciations tookplace, and thecentral Tethys Seawas formed.

50 MILLION YEARS AGOThe continental masseswere in positionssimilar to those oftoday. Some of thehighest mountainranges of today, the

Alps and the Andes,were being formed.Simultaneously, thesubcontinent of Indiawas colliding withEurasia to form thehighest mountainrange, the Himalayas.

200 MILLION YEARS AGO.Laurasia (North America,Europe, and Asia) andGondwana (South Ame-rica, Africa, India, Aus-tralia, and Antarctica)separate from each other.

200 MILLIONYEARS AGOGondwanaseparates, formingAfrica, Antarctica,Australia, India,and South America.

MASS EXTINCTIONS60% OF

SPECIES95% OF

SPECIES75% OF

SPECIES80% OF

SPECIES

CHANGING CLIMATE. The first 20 millionyears of the Cenozoic Era were relativelywarm, but at the end of the period climatechanged, and the polar caps were formed.

PRAIRIES, THE IDEAL STAGE. The spreadof hominin species throughout the planetcoincided with the expansion of prairies asthe dominant form of vegetation.

THE PRESENCE OFOXYGEN. The firstfish, called agnates,had no jaws. Thispteraspis, found inshallow waters,belongs to theSilurian Period.

THE CAMBRIAN EXPLOSION.Numerous multicellular speciessuddenly appeared.

FEATHERED.Titanis was acarnivorous bird.Because of itssize (8.2 feet[2.5 m] tall) andits small wings,it was flightless.

ON FOUR LEGS. This very ancientamphibian, called Acanthostega, lived

during the Devonian Period.

METALDETES had acalcareous structuresimilar to that ofsponges. They lived inthe Cambrian sea.

CRINOID FOSSIL. The fossilsfrom these archaic marine

invertebrates were typical ofthe Silurian Period and are

widely distributed insedimentary rocks.

PREDATOR.Giganotosaurus carolinii was one of the largest carnivorousdinosaurs, with a lengthof 50 feet (15 m). Below,a Tyrannosaurus tooth, 3inches (8 cm).

FINALLY ALONE.Without thethreat of the largedinosaurs, birdsand mammalscould develop.

RELATIVES. The first fossils of Homoneanderthalensiswere found in 1856.They had a commonancestor with Homosapiens.

VERTEBRA. This isa fossil vertebra ofa Barosaurus. Theneck was flexiblethanks to the lightweight of thesebones.

HEAVYWEIGHT. Theheaviest of all knowndinosaurs was theBarosaurus. It iscalculated that itcould have weighedup to 100 tons.

SABER TEETH.Thylacosmilus resembled the felinesof today, but it was a marsupial. The females had apouch for the young, like that of kangaroos. Theirteeth never stopped growing. Their fossils were foundin Argentina; they lived during the Miocene andPliocene epochs, subdivisions of the Neogene Period.

Australopithecus afarensis. A reconstruction of the head of this hominin is shown here. It was an ancestor of the humangenus and lived from 3.7 million to 2.9 million years ago. Witha height of 40 inches (1 m), it was smaller than modernhumans. According to theory, Homo habilis descended from it..

SCALES. The image shows the scalesof a Lepidotus, a type of archaic fish.These were covered by a hard and shinysubstance similar to enamel. Todaymost reptiles and fish have scales.

LAVA BECAME ROCK. The firstterrestrial surface was a thin layerwith scattered volcanoes thatspouted very light lava thatcame from the Earth'sinterior. As the lava cooled,it hardened and thickenedthe early crust.

CE

NO

ZO

IC

ME

SO

ZO

IC

PA

LE

OZ

OIC

PR

EC

AM

BR

IAN

3 billionyears agoThe firstbacteria appear.

4.8 billionyears agoFormation ofthe Earth

2.1 billionyears agoOxygen appears inthe atmosphere.

600 millionyears agoFirst fossils ofmulticellular animals

4 BILLION YEARS AGO

3.8 BILLIONYEARS AGO


The Earth's surface cools andaccumulates liquid water.

Prebiotic evolution in which inert matter istransformed into organic matter

First fossil evidence of life in earlyArchean sedimentary rocks


Chemical ProcessesA

lthough it is assumed today that all life-forms are connected to the presence of oxygen, life beganon Earth more than three billion years ago in the form of microorganisms. They determined, andstill determine today, the biological processes on Earth. Science seeks to explain the origin of life as

a series of chemical reactions that occurred by chance over millions of years and that gave rise to thevarious organisms of today. Another possibility is that life on Earth originated in the form of microbes thatreached the Earth from space, lodged, for instance, within a meteorite that fell to the Earth's surface.

Original CellsThe origin of life on Earth can be inferred from molecular evolution. The firstliving organisms (prokaryotes) began to develop in groups, giving rise to a

process of cooperation called symbiosis. In this way, more complex life-forms calledeukaryotes emerged. Eukaryotes have a nucleus that contains genetic information(DNA). In large measure, the development of bacteria was a chemical evolutionthat resulted in new methods to obtain energy from the Sun and extractoxygen from water (photosynthesis).

The first reactionSome four billion years ago, the atmospherecontained very little free oxygen and carbon

dioxide. However, it was rich in simple chemicalsubstances, such as water, hydrogen, ammonia,and methane. Ultraviolet radiation and dischargesof lightning could have unleashed chemicalreactions that formed complex organiccompounds (carbohydrates, amino acids,nucleotides), creating the building blocks of life. In 1953, Americans Harold Urey and Stanley Millertested this theory in the laboratory.

PLANTSCertain photosynthetic bacteriainvaded eukaryotic cells and becamechloroplasts, originating theancestral plant cell.

ANIMALSCertain aerobic bacteria withrespiratory enzymesconverted intomitochondria and gaverise to the ancestral cellsof modern animals.

Prokaryoteswere the first life-forms, with no nucleus orenveloping membranes. These single-celledorganisms had their genetic codedispersed between the cell walls.Today two groups ofprokaryotes survive: bacteriaand archaeobacteria.

Eukaryoteshave a central nucleus that contains nucleicacid (DNA). The content of the nucleus iscalled nucleoplasm. The substance outsidethe nucleus is called cytoplasm, and itcontains various organelles with differentfunctions. Many are involved in generatingenergy for the organism's development.

NUCLEUScontains a largeamount of geneticinformation instrands of DNAthat give the cellinstructions togrow, function,and reproduce.

NUCLEARPORES

ENDOPLASMICRETICULUMhelps transportsubstances through

the cell and playsa role in fat

metabolism.

RIBOSOMESproduce theproteins thatmake up the cell.

GOLGI BODIESFlat sacs that receiveproteins from the wrinkledendoplasmic reticulum andrelease them through thecell wall

MITOCHONDRIAOrganelle that producesenergy for various cellularfunctions

CELL WALL

FILAMENTS

RIBOSOMES

FREE DNA INTHE INTERIOR

WATER

IN THE PROCESS, THE NEWSUBSTANCES COULD HAVEMADE COPIES OFTHEMSELVES.

AEROBICBACTERIA(ANCESTOR OFMITOCHONDRIA)

AEROBEINCORPORATED

INTO CELL

A

B

PRECURSORS OF EUKARYOTICCELLS

METHANE

AMMONIAHYDROGEN

Roughendoplasmicreticulum

Smooth endoplasmicreticulum

INNERMEMBRANE

OUTERMEMBRANE

TONOPLAST

CHLOROPLASTSOrganelles specialized for obtainingenergy by photosynthesis

NUCLEUS

MITOCHONDRIA

GOLGI BODY

VACUOLEtransports andstores substancesingested throughwater.

PROKARYOTEINCORPORATEDINTO THE CELL

PHOTOSYNTHETICPROKARYOTE

LYSOSOMESbreak down and eliminateharmful substances withpowerful enzymes.

CENTRIOLEKey structure for celldivision, located in thecenter of the cell

MICROTUBULES

PLASMAMEMBRANE

4.2 BILLION YEARS AGO

The Earth's atmosphere sets itaside from the other planets.

Volcanic eruptions and igneous rockdominate the Earth's landscape.

ARCHEAN4.6 BILLION YEARS AGO


Fossil Relics T

he term proterozoic comes from the Greek proteros (“first”) and zoic (“life”) and is thename given to an interval of geologic time of about two billion years at the end of whatis known as Precambrian time. The oldest fossils of complex organisms yet found, in

the Ediacara fossil bed (Australia), date from the end of the Proterozoic, in theNeoproterozoic Era. It is the first evidence of multicellular organisms with differentiatedtissues. It is believed that the specimens of Ediacara life were not animals butprokaryotes that were formed of various cells and did have internal cavities.Toward the end of the Proterozoic, there was a global disturbance in the carboncycle that caused the disappearance of most complex organisms and openedthe way for the great explosion of life in the Cambrian Period.

MAWSONITEThis species of cnidarian shiftedslowly through the waters, aided bythe currents. It contracted its long,thin umbrella, extending its tentaclesand shooting its microscopic harpoonsto capture its prey. For this, it alsoused a kind of poison.

CYCLOMEDUSAAncient circular fossil with a bump inthe middle and up to five concentricridges. Some radial segments extendalong the length of the outer disks.

CHARNIAis one of the largest fossils ofthe Ediacaran Period. Its flat,leaf-shaped body wassupported by a disklikestructure.

KIMBERELLAAn advanced metazoan from theEdiacara fauna, it is the firstknown organism with a bodycavity. It is believed to have beensimilar to a mollusk and wasfound in Russia in 1993.

TRIBRACHIDIUMIt is believed that this species,developed in the form of a diskwith three symmetric parts, is adistant relative to corals and toanemones such as starfish.

DICKINSONIAUsually considered an annelid wormbecause of its similar appearance to anextinct genus (Spinther). It also may be aversion of the soft body of the bananacoral fungus.

are the most ancient evidence of lifeknown on Earth, and even today theyhave maintained their evolutionaryline. They are laminated organic-sedimentary structures, principallycyanobacteria and calcium carbonate,stuck to the substrate product ofmetabolic activity. They grew in mass,which led to the formation of reefs.

STROMATOLITES

CALCIUMCARBONATE

CYANOBACTERIA

3.5-4 inches(9-10 cm)

IN DIAMETER

1 inch(2.5 cm) IN LENGTH

8 inches(20 cm) IN LENGTH

40 inches(100 cm) MAXIMUM LENGTH

2 inches(5 cm)

IN DIAMETER

IN LENGTH

Primitive SpeciesIt has been established that the animals of theEdiacara were the first invertebrates on the

Earth. They appeared approximately 650 million yearsago and were made up of various cells. Some had a softflat body while others were in the form of a disk or along strip. A relevant fact about the life of this period isthat they no longer had only one cell that was in chargeof feeding, breathing, and reproducing; instead, thediverse cells specialized in distinct functions.


600 MILLIONYEARS AGO

3 BILLIONYEARS AGO

Accumulation of iron oxideon the seafloor

Extensive glaciationtakes place.

Multicellular marine organismscalled Ediacara fauna develop.

40 inches(100 cm)


The Cambrian ExplosionU

nlike the previous development of microbial life, the great explosionof life that emerged in the Cambrian some 500 million years agogave rise to the evolution of a diversity of multicellular

organisms (including mollusks, trilobites, brachiopods, echinoderms,sponges, corals, chordata) protected by exoskeletons or shells. Itis believed that this group of organisms represents thecharacteristic fauna of the Cambrian. The Burgess Shalefossil bed in British Columbia (Canada) holds a large numberof fossils of soft-bodied animals of the period and is one ofthe most important fossil formations in the world.

PRIAPULIDSBenthic worms thatlive buried in sandand in the mud ofshallow water aswell as in deepwater. There areabout 15 species.

SPONGESThey grew primarilyon the seabed inBurgess Shale andfrequently developedalongside algae ofdiverse species,sizes, and shapes.

ANOMALOCARISThe largest plundering arthropod known of that time, it hada circular mouth, appendages that allowed it to stronglygrasp its prey, and fins along the length of both sides thatwere used for swimming. In comparison to other organisms,it was a true giant of Burgess Shale.

(60 cm) 24 inchesTHE LENGTH REACHED BYTHIS SPECIES

IN LENGTH

0.8 inch(2 cm)

(3 cm) maximum length 1.2 inchesOF THIS ARTHROPOD

Comparisonto humanscale

(10 cm) long 4 inchesINCLUDING THE TAIL

PIKAIAOne of the first chordates, similar to aneel, with a tail in the shape of a flipper.It is the oldest known ancestorto vertebrates.

MARELLASmall swimming arthropod thatwas probably an easy prey forpredators in Burgess Shale.

HALLUCIGENIAHad a defense system based on long spines thatsimultaneously servedas feet for itsmovement.

4 inches(10 cm) in length TO THE EXTREMITIES

Provided with a strongexoskeleton, theAnomalocaris was a trueterror in the Cambrian seas.

Burgess ShaleLocated in Yoho National Park in the Canadian province ofBritish Columbia, Burgess Shale is a celebrated fossil bed

found in 1909 by the American paleontologist Charles Walcott.Burgess Shale offers a unique look at the explosion of Cambrian life.It contains thousands of very well—preserved fossilizedinvertebrates, including arthropods, worms, and primitive chordata,some with their soft parts intact.

CAMBRIANBEGINS

THE EVOLUTIONARYEXPLOSION

CORALREEFS

The increased presence of oxygenpermitted the formation of shells.

The Cambrian originated agreat variety of body designs.

are formed by the calcareousskeletons of innumerable softbodied animals.

0.4 inch(10 mm)

CAMBRIAN(542 TO 488 MILLION YEARS AGO)

FIRST FISH AND PLANTS

The success of the vertebrates in the colonizationof land came in part from the evolution of theamniotic egg covered in a leathery membrane. Inthe evolution of plants, pollen made themindependent of water.

0.2 inch (6 mm)

28 ORIGIN OF LIFE

Conquest of the EarthT

he Paleozoic Era (ancient life) was characterized by successivecollisions of continental masses, and the occupation of their interiorlakes made possible the appearance of primitive terrestrial plants, the

first fish adapted to freshwater, and amphibians, highlighting a keyevolutionary event: the conquest of the terrestrial surface some 360 millionyears ago. For this process, diverse mechanisms of adaptation were necessary,from new designs of vascular plants and changes in the bone and muscularstructures to new systems of reproduction. The appearance of reptiles andtheir novel amniotic egg meant the definitive colonization of the land by thevertebrates, just as the pollen made plants completely independent of water.

EVOLUTION AND GENETICS 29

From fins to limbs The amphibian evolution facilitated theexploration of new sources of foods, such as

insects and plants, and an adaptation of the respiratorysystem for the use of oxygen in the air. For this purpose,the aquatic vertebrates had to modify their skeleton (agreater pelvic and pectoral waist) and developmusculature. At the same time, the fins transformedinto legs to permit movement on land.

New breed of fishAfter the decline of the trilobites and the appearance ofcorals, crinoids, bryozoa, and pelecypods came the fish

with external bony shields and no jaws, which are the first—known vertebrates. During the Silurian Period, the cephalopodsand jawed fish abounded in a globally warm climate. Theadaptation of the fish as much to freshwater assaltwater coincided with the predominance ofboned fish, from which amphibians developed.

Comparison tohuman scale

DUNKLEOSTEUSComparison to human scale

DORSAL SPINEIts system of joints, called zygapophyses,between the vertebrae helps to maintainthe rigidity of the dorsal spine.

PERMIAN299 TO 251 MILLION YEARS AGO

CARBONIFEROUS359 TO 299 MILLION YEARS AGO

DEVONIAN416 TO 359 MILLION YEARS AGO

ORDOVICIAN488 TO 444 MILLION YEARS AGO

SILURIAN444 TO 416 MILLION YEARS AGO

The first land organisms appear—lichens and bryophytes.

Great coral reefs and sometypes of small plants

Vascular plants and arthropods formdiverse terrestrial ecosystems.

Land tetrapods and wingedinsects appear.

Large variety of insects andvertebrates on land

DEVELOPMENT OFVESSELS IN PLANTS

The need to transport waterfrom the root to the stem andto transport photosyntheticproducts in the oppositedirection in plants inducedthe development of a systemof internal vessels.Reproduction based on pollenachieved the definiteconquest of the terrestrialenvironment.

AIR CHAMBER

Pollenguarantees

reproduction.

Thinlobular fin

Internalvessel

conductors

AMNION ALLANTOIS

EMBRYO

SHELL

ALBUMIN

YOLK SAC

CHORION

BONE STRUCTUREOnly three bones (humerus,cubitus, and radius) formedthe bone support of thelegs. Unlike fish, it had atype of mobile wrist andeight fingers that moved allat once like a paddle.

PREDATORThe development of alarge mouth allowed itto hunt othervertebrates.

FINTo move itself through thewater, the acanthostegamoved its fin, sweepingfrom side to side. Itmaintained thischaracteristic in its move to land.

Bony teeth withsharpenedvertexes

Head and chestplates connected

Dorsalfin

0.2 inch(6 mm)

The DevonianPeriod is known asthe age of fish.

Skull andjaw of abarracuda

(9 m) 30 feetTHE LENGTH REACHED BYDUNKLEOSTEUS

(90-120 cm) 35-47 inchesMAXIMUM LENGTH

JAWThe key in the evolution of thevertebrates, allowing apredatory way of life, sincethey could now firmly graspprey, manipulate it, and cut it

ACANTHOSTEGA

MEGANEURA


The Reign of the DinosaursF

rom abundant fossil evidence, scientists have determined that dinosaurs were the dominant formof terrestrial animal life during the Mesozoic Era. There was a continual change of dinosaurspecies. Some of them lived during the three periods of the Mesozoic Era, others throughout two,

and some in only one. Unlike the rest of the reptiles, the legs of dinosaurs were placed not toward theside but under the body, as they appear in mammals. This arrangement, together with its bonestructure (a femur articulated to a hollow pelvis) significantly aided its locomotion. In their evolution,the dinosaurs also developed such defensive features as horns, claws, hornlike beaks, and armor. It was long believed that dinosaurs were cold-blooded; nevertheless, thedominant hypothesis today is that they were warm-blooded. Theymysteriously became extinct toward the end of the Cretaceous Period.

Triassic PeriodFollowing the massive extinction andbiological crisis at the end of the Permian Period,

only a relatively few species of plants and animals were ableto survive. In the Triassic, the regeneration of life slowly began.Mollusks dominated in marine environments, and reptiles dominatedon land. As for plants, families of ferns, conifers, and bennettitalesappeared during the middle and late Triassic.

Jurassic PeriodThe increase in sea levels inundated interior continental regions, generatingwarmer and more humid environments that favored the development of life. The

reptiles adapted to diverse environments, and the dinosaurs developed greatly. Duringthis period, there are examples of herbivore dinosaurs existing together with carnivorousdinosaurs. Freshwater environments were favorable for the evolution of invertebrates,amphibians, and reptiles such as turtles and crocodiles. The first birds emerged.

Cretaceous PeriodIn this period, carnivorous dinosaurs appeared with claws curved in theshape of a sickle, specially designed to gut its prey. A prime example is the

claw of Baryonyx. It measures 12 inches (30 cm), a disproportionate length for ananimal 30 feet (9 m) in length. During the Cretaceous Period, the evolution ofinsects and birds continued, and flora that made use of pollination developed.Nevertheless, this period was markedboth by a revolution in the seas (theappearance of new groups ofpredators, such as teleost fish andsharks) and by a revolution on land(the extinction of the dinosaurs about65 million years ago).

PLATEOSAURUS(FLAT REPTILE)

MAMMALSAt the end of the Triassic, there are traces of mammals, which evolved fromcynodont reptiles. Among the mammalian characteristics that made theirappearance were elongated and differentiated teeth and a secondary palate.

The Plateosauruswalked on four legs

but could reachelevated foliage withsupport from its tail.

FERN PALM CONIFER GINGKO

BIPEDALISMThe Allosaurus, a giant therapodcarnivore, was one of the firstspecies to move about on two legs.

HORSETAIL CONIFER

HOLLY BEECH OAKWALNUT

CRETACEOUS146 TO 65.5 MILLION YEARS AGO

Present-day oceans andcontinental masses are defined.

JURASSIC200 TO 146 MILLION YEARS AGO

Fragmentation of Pangea andincrease in sea level

TRIASSIC251 TO 200 MILLION YEARS AGO

The equatorial supercontinentof Pangea forms.

EXTINCTIONAbout 65 million years ago, all land animals larger than about 55pounds (25 kg) disappeared. It is believed that the dinosaurs lostin the competition for food to insects and small mammals.

Up to 50feet (15 m)

Up to 30 feet(9 m)

Up to 33 feet(10 m)

GIGANOTOSAURUS (GREATSOUTHERN LIZARD)

COMPARATIVE SIZE

STEGOSAURUS (ROOFED LIZARD)

32 ORIGIN OF LIFE EVOLUTION AND GENETICS 33

The End of the Dinosaurs

More Theories About the “K-T Boundary”The period between the Cretaceous and Paleogene periods, known as the “K-Tboundary,” marks the end of the era of the dinosaurs. Although the impact

theory is widely accepted, other theories suggest that there was a great change inclimate that caused dinosaurs to become extinct very slowly as the shallow seaswithdrew from solid land. According to the defenders of these theories, the dinosaurswere being reduced in variety and number throughout a period that lasted millions ofyears. The large meteorite of Chicxulub, according to this hypothesis, would havefallen some 300 thousand years before the end of the Cretaceous Period. It has alsobeen hypothesized that mammals proliferated before the extinction and fed on reptileeggs, or that the plants eaten by the large sauropods succumbed to diseases.

WAS THE DIAMETER OF THEMETEORITE THAT FELL IN

CHICXULUB.

6 miles(10 km)

OF LIVINGSPECIES

became extinct atthe same time.

50%

K-T BOUNDARY65 MILLION YEARS AGO

Sudden climatologic change,65 million years ago

PALEOGENE65.5 TO 23 MILLION YEARS AGO

Beginning of the Cenozoic Erawhich extends to the present.

Chicxulub, Mexico

ATOMIC BOMBS is the equivalent, according tocalculations, of the energyunleashed by the impact inChicxulub.

million

POST-EXTINCTIONsedimentsaccumulated in theCenozoic Era.

DUST AND ASHFrom the impact ofthe fireball

EJECTED ROCKMaterial from thecrater that hassettled

PRE-EXTINCTIONSediments withfossils of dinosaurs

IN THE ROCKSIn the region of theYucatán, rocks made ofmeteorite fragments arecommonly foundcompressed among the(darker) mineralsediments.

VOLCANIC ERUPTIONSAnother theory relates the massiveextinction with the appearance of prolongedvolcanic eruptions on Earth that emittedasphyxiating gases and darkened the skieswith dust. Thousands of cubic miles ofvolcanic rock found on a plateau in Deccan,India, support this theory.

B SPACE CATACLYSMEvery 67 million years, the Solar Systemcrosses through the plane of the Milky Way.At those times some stars in the Milky Waycan cause comets to escape from the Oortcloud and enter the inner Solar System. It ispossible that one of these bodies could haveimpacted the Earth.

C

Profound EvidenceIn the Mexican town of Chicxulub, on theYucatán Peninsula, there is a depression62 miles (100 km) in diameter that isattributed to the impact of a meteoriteabout 65 million years ago. The layers ofrock that make up the soil support thistheory and make it possible to see whatoccurred before and after the impact.

A

50

Dinosaurs reigned over the Earth until about 65 million years ago. All of a suddenthey died out because of a drastic change in the conditions that made their lifepossible. The most reasonable hypothesis for this change attributes it to the

collision of a large asteroid or comet with the Earth. The resulting fire devastated allof what today are the North and South American continents. The impact raised hugedust clouds that remained suspended in the air for months, darkening the planet. Atthe same time, sulfur, chlorine, and nitrogen was mixed into dense clouds, causingkilling acid rains.

Theropithecusoswaldi

Size similar to a human, 3 to6 feet (1-2 m)

COMPARATIVESIZE

After the extinction of the large dinosaurs at the end ofthe Mesozoic Era, mammals found the opportunity toevolve until becoming sovereigns of the Earth. The

Cenozoic Era, which began 65.5 million years ago, also sawthe appearance and evolution of plants with flowers, andlarge mountain chains of today (the Himalayas, the Alps, andthe Andes) formed. Within the zoological class of mammals,primates appeared, as did the Homo genus, the immediateancestors of humans, toward the end of the era.

Mammals are represented by marsupials,prosimians, and ungulates.

Hominoids disperse from Africato all over the world.


The Class that Defines an EraSome 220 million years ago, the mammaliaformesappeared, which today are all extinct. More similar to

reptiles, they already had larger skulls and were beginning to raisetheir stomachs from the ground with the strength of their limbs.And 100 million years ago, the two predominant survivingsuborders appeared—the marsupials (which remain only inOceania, with the exception of the American opossum) and theplacentals (which colonized the entire Cenozoic world).

PREHENSILE THUMBOne finger opposite the rest,predecessor to the thumb ofhumans, allowed thisEuropean monkey of thePliocene to manipulateobjects (5 million years ago).LONG CLAWS

With these it huntedinsects and dug holes tohide from dinosaurs.

SHORT TAILThe appendage of thevertebral column, itended in a point. Thisdifferentiates it frompresent-day rodents.

CONTINENTS OFTHE PAST

PRESENT-DAYCONTINENTS

LONG FINGERSare what firstpermitted theanthropoids to holdonto the branchesand move throughthe trees.

TAILThey used it forclimbing equilibrium. InAmerican monkeys, thetail was prehensile: itallowed them to hangfrom branches.

New Plants The vegetation that appearedafter the extinction of thedinosaurs was very differentfrom previous forms. In thePaleocene and Pleistocene, atropical climatepredominated, but afterwardthe species of temperateclimates have excelled to thepresent.

Ancestors ofHumans

Primates are mammals that arecharacterized by binocular vision,

the large relative size of their brains, andthe prehensile limbs that allowed them,among others things, to take to the branchesof trees and make use of objects asrudimentary tools. The first primates (calledPurgatorius) appeared in North America in thePaleocene Epoch. The oldest fossils of monkeys(anthropoids) date from some 53 million years ago,but the origin is still uncertain.

PRIMATESAPPEAR IN THECENOZOIC ERA.

GRASSES(PLIOCENE)60

millionyears ago

SINCE THE APPEARANCE OFPRIMATES ON EARTH

200million

yearsMAMMALS HAVE

BEEN ON LAND

MORGANUCODON

Extinct insectivorous rodent of theJurassic (200 million years ago)

Its total length was 6 inches (15 cm), and it weighed from 1 to 2 ounces (30-50 g).

COMPARATIVE SIZE

Development of the first Homo sapiens.

PLEISTOCENEFROM 1.8 MILLION TO 12,000 YEARS AGO

First fossil records of Homo sapiens sapiens

HOLOCENEFROM 12,000 YEARS AGO TO THE PRESENT

Land of Mammals

FICUS(EOCENE)

SYCAMORE(PALEOCENE)

RANUNCULUS(PLEISTOCENE)

One of thefirst plantswith flowers

SPRUCE(PLEISTOCENE)

Establishment ofthe conifers

PALEOGENE65.5 TO 23 MILLION YEARS AGO

NEOGENEFROM 23 MILLION YEARS AGO

36 ORIGIN OF LIFE

The Tree of LifeH

ere is a visual representation to explain how allliving beings are related. Unlike genealogical trees,in which information supplied by families is used,

phylogenetic trees use information from fossils as well asthat generated through the structural and molecularstudies of organisms. The construction of phylogenetictrees takes into account the theory of evolution, whichindicates that organisms are descendants of acommon ancestor.


This classification technique is based on theevolutionary relationship of species coming from

similar derived characteristics and supposes a commonancestor for all living species. The results are used to form adiagram in which these characteristics are shown asbranching points that have evolved; at the same time, thediagram places the species into clades, or groups. Althoughthe diagram is based on evolution, its expression is inpresent-day characteristics and the possible order in whichthey developed. Cladistics is an important analytical system,and it is the basis for present-day biological study. It arisesfrom a complex variety of facts: DNA sequences,morphology, and biochemical knowledge. The cladogram,commonly called the tree of life, was introduced in the 1950sby the German entomologist Willi Hennig.

Cladistics

The scientific evidence supports the theorythat life on Earth has evolved and that all

species share common ancestors. However, thereare no conclusive facts about the origin of life. It isknown that the first life-forms must have beenprokaryotes, or unicellular beings, whose geneticinformation is found anywhere inside their cellwalls. From this point of view, the archaea areprokaryotes, as are bacteria. For this reason, theywere once considered to be in the same kingdom ofliving things, but certain characteristics of genetictransmission places them closer to the eukaryotes.

Relationships

EukaryotaThis group consists of species that have a truenucleus in their cellular structure. It includesunicellular and multicellular organisms, which

are formed by specialized cells that do notsurvive independently.

ProtistaA paraphyletic group, it includes the species thatcannot be classified in any other group. There are,

therefore, many differences among protistaspecies, such as algae and the amoeba.

PlantsMulticellular autotrophic organisms;

they have cells with a nucleus and thickcellular walls that are grouped inspecialized tissues. They carry out

photosynthesis by means ofchloroplasts.

FungiCellular heterotrophic organisms withcell walls thickened with chitin. They

carry out digestion externally andsecrete enzymes to reabsorb the

resulting molecules.

AnimalsMulticellular and heterotrophic. Two of their

principal characteristics are their mobility andtheir internal organ systems. Animals reproduce

sexually, and their metabolism is aerobic.

BILATERALSymmetrical

bilateralorganisms

ARTHROPODShave an external

skeleton(exoskeleton). Their

limbs are jointedappendages.

CRUSTACEANSCrabs and ocean

lobsters

INSECTSThe greatestevolutionarysuccess

ARACHNIDSSpiders,scorpions, andacarids

MYRIAPODSMillipedes andcentipedes

NOT VASCULARNo internal vessel

systemVASCULAR

Internal vesselsystem

GYMNOSPERMWith naked seeds;

cycadophytes were examples.

ANGIOSPERMWith flower and fruit.More than 250,000

species form this group.

SEEDLESSThey are small plantswith simple tissues.

WITH SEEDSome have exposedseed and some have

flower and fruit.

VERTEBRATEShave a vertebral

column, a skull thatprotects the brain,

and a skeleton.

TETRAPODSAnimals with

four limbs

AMNIOTESSpecies that are bornfrom an embryo inside

an amniotic egg

AMPHIBIANSWhen young they arewater dwellers; later

they live on land.

CARTILAGINOUSFISH

include the rays andsharks.

CNIDARIANSinclude species

such as thejellyfish and

corals.

Humans belong to the class Mammaliaand specifically share the subclass of theplacentals, or eutherians, which meansthat the embryo develops completelyinside the mother and gets its nutrientsfrom the placenta. After birth, it dependson the mother, who provides thematernal milk in the first phase ofdevelopment. Humans form part of theorder Primates, one of the 29 orders inwhich mammals are divided. Within thisorder, characteristics are shared withmonkeys and apes. The closest relativesto human beings are the great apes.

Humans

The evolution of this feature allowed thetetrapods to conquer land and to adaptto its distinct environments. In amniotespecies the embryo is protected in asealed structure called the amniotic egg.Among mammals, only monotremes

continue to be oviparous; however, inthe placental subclass, to which humansbelong, the placenta is a modified egg.Its membranes have transformed, butthe embryo is still surrounded by anamnion filled with amniotic fluid.

Amniotes

DEUTEROMYCETESAsexual

reproduction

BASIDIOMYCETESinclude the typicalcapped mushrooms.

ZYGOMYCETESreproduce throughzygospores.

COCCALSThe pneumococcals

are an example.

EURYARCHAEOTAHalobacteria

salinarum

CRENARCHAEOTAlive in environments with

high temperatures.

KORARCHAEOTAThe most primitive

of the archaea

BACILLUSEscherichia colihas this form.

SPIRILLUMIn the form of ahelicoid or spiral

VIBRIOFound insaltwater

CHYTRIDIOMYCETEScan have mobile cells.

10,000,000SPECIES OF ANIMALS ARE CALCULATED TO

INHABIT THE EARTH IN THEIR DISTINCTENVIRONMENTS.

BIRDS AND REPTILESOviparous species. Reptiles are

ectothermic (cold-blooded).

MAMMALSThe offspring are fedwith mother's milk.

PLACENTALThe offspring areborn completelydeveloped.

MONOTREMESThe only oviparousmammals. They arethe most primitive.

MARSUPIALSThe embryo finishesits developmentoutside of themother.

TURTLESThe oldest

reptiles

SNAKESScaly and with

long bodies

LIZARDS Also includes

crocodiles

ASCOMYCETESMost species are

grouped here.

BONY FISHhave spines and a jaw.

ABOUT

5,000SPECIES OF MAMMALS

ARE INCLUDED IN THREEGROUPS.

MOLLUSKSinclude the

octopus, snails,and oysters.

ArchaeaThese organisms are unicellular and

microscopic. The majority are anaerobicand live in extreme environments. About

one half of them give off methane intheir metabolic process. There are more

than 200 known species.

BacteriaUnicellular organisms that live on

surfaces in colonies. Generally they haveone cellular wall composed of

peptidoglycans, and many bacteria havecilia. It is believed that they existed as

long as three billion years ago.

DIRECT ANCESTORS 48-49

CULTURE, THE GREAT LEAP 50-51

URBAN REVOLUTION 52-53

Human Evolution

Homo sapiens, the name thatscientifically designates ourspecies, is the result of a longevolutionary process thatbegan in Africa during the

Pliocene Epoch. Very few fossils havebeen found, and there are no clear cluesabout what caused the amazingdevelopment of the culture. Somebelieve that a change in the brain or

vocal apparatus permitted theemergence of a complex language. Othertheories hypothesize that a change in thearchitecture of the human mind allowedHomo sapiens to use imagination. What

is certain is that hunting and gatheringwas a way of life for 10,000 years untilpeople formed settlements after the IceAge and cities began to emerge.

HUMAN EVOLUTION 40-41

FIRST HUMANS 42-43

USE OF TOOLS 44-45

ABLE HUNTERS 46-47

NEANDERTHALOur close cousin was strong,an able hunter, and anexcellent artisan. Nobody canexplain why the Neanderthalsdisappeared.

FREE ARMS

EVOLUTION AND GENETICS 4140 HUMAN EVOLUTION

HumanEvolutionP

erhaps motivated by climatic change, some fivemillion years ago the species of primates thatinhabited the African rainforest subdivided,

making room for the appearance of the hominins, ourfirst bipedal ancestors. From that time onward, thescientific community has tried to reconstructcomplex phylogenetic trees to give an account of therise of our species. DNA studies on fossil remainsallow us to determine their age and their linkswith different species. Each new findingcan put into question old theories aboutthe origin of humans.

Primates That TalkThe rise of symbolic language, which is aunique ability of humans, is a mystery.

But the evolution of the speech apparatus inhumans has been decisive. The human larynx islocated much lower than in the rest of themammals. This characteristic makes it possibleto emit a much greater variety of sounds.

Homohabilis

Homoerectus

Homosapiens

THE GREAT LEAPIts brain was much greater, and therewere substantial anatomical changes.

MIGRANTThis is the species thatleft Africa and rapidlypopulated almost all theOld World. From theform of its larynx, it isdeduced that Homoerectus could talk.

FUNCTION OF SPEECHIn humans, speech has a semanticcharacter. Upon speaking, ahuman always addresses otherpeople with the object ofinfluencing them, changing theirthoughts, enriching them mentally,or directing their conduct toward

something specific. Somescientists believe that a change inthe brain or vocal apparatusallowed the development ofcomplex language, whichfacilitated creativity and theacquisition of knowledge.

AND FOR THINKINGThe evolution of the brain hasbeen essential for thedevelopment of language andother human capacities.Greater cranial capacity andnutrition have hadphysiological influences.

TOOLS FOR SPEAKINGThe larynx of humans islocated much lower than inchimpanzees and thus allowshumans to emit a greatervariety of sounds.

CHIMPANZEE MAN CHIMPANZEE MAN

LARYNX

VOCALCORDS

HUNTER-GATHERERVery similar to H.sapiens; nevertheless, itis not its ancestor, but aspecies that emergedfrom H. erectus.

CULTURALANIMALThe only survivingspecies of the Homogenus. Its evolutiontook place notthrough genetics butthrough culture.

THE PHYLOGENETIC TREEThis cladogram (map of emergence ofnew species from previous ones) showsthe relationship of the Homo genus tothe other species of primates.

BIPEDALISMrequires less

energy to moveand leaves the

hands free.

GROWTHIt is calculated thatthe growth of thebrain is 44 percentlarger with respectto Australopithecus,an enormousdevelopment inrelation to the body.

BONESThose of the handsand legs are verysimilar to those ofmodern humanbeings.

UPRIGHTPOSTUREWalking on twolegs led to aweakening of the neckmuscles and astrengthening of the hipmuscles.

STABLEMOVEMENTWith the femurforming an angletoward the inside,the center of thebody mass isrearranged; thispermits stablebipedal movement.

SIZEIt already hadthe stature ofHomo sapiensbut wasstronger.

THICKNESSIts bones,including thecranium, werethicker thanthose in previousspecies.

Gorillas,chimpanzees, andhominins had acommon ancestorat least fivemillion years ago.

NOT-SO-DISTANTRELATIVES

There are various uncertaintiesand disagreements amongpaleontologists about how theevolutionary tree for homininsbranches out. This version is based on one created bypaleoanthropologist Ian Tattersall.

4 MILLION YEARS AGO

1 MYA

5 MYA

10 MYA

15 MYA

20 MYA(MILLION YEARS AGO)

2 MILLION YEARS AGO 1 MILLION YEARS AGO TODAY

MAN CHIMPANZEE GORILLA ORANGUTAN

MUSCLESSome prominentmuscle markingsand thickreinforced areasof the bonesindicate thatthe body of H.erectus couldsupport strongmovement andmuscle tension.

ADAPTATIONIts short, robustphysique showsgood adaptationto cold climates.

CHESTThe rib cageopened slightlyoutward.

ABILITYIt already wasusing sticks androcks as tools.

ARDIPITHECUS AUSTRALOPITHECUS

PARANTHROPUS HOMO

A. ramidus A. anamensis

P. aethiopicus

P. boisei

P. robustus

H. habilis

H. rudolfensis

H. ergaster H. erectus

H. heidelbergensis

H. neanderthalensis

H. sapiensA. africanus

???

A. garhi

A. afarensis

Homo neander-thalensis

Australo-pithecusPRECURSORThis ape was the firsttrue hominin but isextinct today.

AUSTRALOPITHECUSANAMENSIS

AUSTRALOPITHECUSAFRICANUS

PARANTHROPUSAETHIOPICUS

PARANTHROPUSBOISEI

PARANTHROPUSROBUSTUS

4.2 to 3.9 million years ago. Primitivehominin with wide molars.

3 to 2.5 million years ago. Globularskull with greater cerebral capacity.

Approximately 2.5 million yearsago. Robust skull and solid face.

2.2 to 1.3 million years ago. Skull adaptedfor consumption of tough vegetables.

1.8 to 1.5 million years ago.Very robust, bony appearance.


First Humans

Adaptation to the Environment

The climatic changes that occurred during theMiocene probably transformed the tropical

rainforest into savannah. Various species ofhominins left their habitats in the treesand went down to the grasslands insearch of food. It is conjectured thatthe first hominins began to stand up tosee over the grasslands.

LAETOLIIn 1975 in Laetoli (Tanzania),tracks of hominins thatarchaeologists found infossilized volcanic ashprovided evidence of hominins walking on twolegs (bipedalism).

SKULL OF TAUNGHad a round head andstrong jaw. Its cranialcavity could house abrain (adult) of 26 cubicinches (440 cu cm).

THE SKELETON OF LUCYThis hominid found in Ethiopia had the sizeof a chimpanzee, but its pelvis allowed it tomaintain an upright position.

3.6 FEET(1.1 M)

6 FEET(1.8 M)

Considered the oldest hominin, it inhabitedeastern Africa between three and four millionyears ago. A key aspect in human evolutionwas the bipedalism achieved by A. afarensis.The skeleton of “Lucy,” found in 1974, wasnotable for its age and completeness.

AUSTRALOPITHECUSANAMENSIS

PARANTHROPUSAETHIOPICUS

AUSTRALOPITHECUSAFRICANUS

PARANTHROPUSBOISEI

COMPARATIVESIZE

BIPEDALISMBy walking on two feet,they were able to freetheir upper limbs whilethey moved.

SPECIAL TEETHThey had large incisors like spatulasin front, and the teeth becamearranged in the form of an arch.

PARANTHROPUSROBUSTUS

Imagereconstructedfrom thebones ofLucy.AUSTRALOPITHECUS

AFARENSISAUSTRALOPITHECUSAFARENSIS

Skullfragment

Inferior jaw

Humerus

Part of thehumerus

Elbowjoint

Femalepelvis

Handbone

Wrist bone

Rib

Ulna

Sacrum

Femur

Tibia

Tarsus

Knee joint

Fibula

Clavicle

millionyears ago

3

millionyears ago

3.6

millionyears ago

2.5

Australopithecus afarensis

Metatarsus Phalanx

Brain

Jaw

Archaeological FindingsThe fossil skull of a child was found in 1924 in theTaung mine (South Africa). The remains included

the face with a jaw and tooth fragments as well as skullbones. The brain cavity had been replaced with fossilizedminerals. Later, in 1975, footprints of hominins werefound in Laetoli (Tanzania). It is believed that more thanthree million years ago, after a rain that followed avolcanic eruption, various specimens left their tracks inthe moist volcanic ash.

DORSAL SPINEhad many curves to maintain balance.Given that monkeys do not have lumbars,the weight of the body falls forward.

ADAPTED PELVISMorphological changesin the pelvis, sacrum,and femur made thesebones similar to thosein modern humans.

KNEEUnlike chimpanzees,the rim of the femurhad an ellipticalshape like that in thehuman knee.

TOEWhereas in chimpanzees the big toe isused to grasp, the position of the big toeand the foot arch in hominins supportedmovement in a bipedal posture.

H. SAPIENSGORILLA

GORILLA HUMAN

África(con

The Australopithecus were the first humanlike creatures whocould walk in an upright posture with their hands free, asindicated by the fossils found in Tanzania and Ethiopia. It is

believed that climatic changes, nutritional adaptations, and energy storagefor movement contributed to bipedalism. In any case, their short legs and longarms are seen as indications that they were only occasional walkers. Their craniumwas very different from ours, and their brain was the size of a chimpanzee's. Thereis no proof that they used stone tools. Perhaps they made simple tools with sticks, but they lacked the intelligence to make more sophisticated utensils.

LOCATION OF THE REMAINSOF THE FIRST HOMINIDS

AFRICA


The emergence of Homo habilis, which had a more humanlike appearance thanAustralopithecus, in eastern Africa showed important anatomical modifications thatallowed advancement, especially in the creation of various stone tools, such as flaked

pebbles for cutting and scraping and even hand axes. The bipedal posture for locomotion wasestablished, and the first signs of language appeared. Stone technology became possible thanks tothe notable increase in brain size in Homo habilis. In turn, the anatomic development of Homoerectus facilitated its migration toward areas far from its African origins, and it appears to havepopulated Europe and Asia, where it traveled as far as the Pacific Ocean. Homo erectus was capable

of discovering fire, a vital element that improved humannutrition and provided protection from the cold.

THE BRAINThe cranial cavity of Homohabilis was larger than that ofAustralopithecus, reaching acerebral development ofbetween 40 and 50 cubicinches (650-800 cu cm). It isbelieved that thischaracteristic was key indeveloping the capacity ofmaking tools, considering thatit had half the brain size ofmodern humans.

COMPARATIVESIZES

ARCHAEOLOGICAL FINDINGSThe first being known as Homo habilis was found in 1964 in theOlduvai Gorge, located in the Serengeti Plain (Tanzania). Thelater discovery of the Turkana Boy (Kenya) revealed many ofthe physical particularities of Homo erectus.

FIREOne of the major discoveries in theevolution of humans. It was used notonly for protection from the cold butalso to treat wood and cook food.The first evidence of the use of fire is some 1,500,000 years ago.

HAND AX INTHE SHAPEOF A DROP

HOMO ERECTUS

SKULL OF HOMOHABILIS FOUND INOLDUVAI (TANZANIA)

Homo habilisThe appearance of Homo habilis in eastern Africa between 2 and1.5 million years ago marked a significant advancement in the

evolution of the human genus. The increased brain size and otheranatomical changes together with the development of stonetechnology were substantive developments in this species, whosename means “handy man.” Although it fed on carrion, it was still notcapable of hunting on its own.

Homo erectus The “erect man” is native to East Africa, and its age is estimated at 1.8 millionyears. It was the first hominin to leave Africa. In a short time it populated a great

part of Europe. In Asia it reached China to the east and the island of Java to thesoutheast. Much of what is known about this species was learned from a finding calledTurkana Boy near Lake Turkana, Kenya, in 1984. This species was tall and had longlimbs. The brain of this specimen was larger than that of Homo habilis, and it could havemade the fundamental discovery of making fire.

THIS CARVEDROCK IS THEOLDEST KNOWNTOOL.

SKULL OF HOMOERECTUS FOUND INKOOBI FORA (KENYA)

HOMOHABILIS

6 FEET (1.8 M)

5.3 FEET(1.6 M)

5 FEET(1.3 M)

HOMOERECTUS

HOMOSAPIENS

HOMO HABILIS HOMO ERECTUS

2.5 MILLIONYEARS AGO



ABOUT 1.5 MILLIONYEARS AGO

Appearance of Homo habilisin eastern Africa.

Homo erectus is the firsthominin to leave its habitat.

Homo habilis disappearsbecause of unknown causes.

First use of fire by Homoerectus, in southern Africa

Use of Tools

CARVING The first step wasto select rocksand scrape themuntil sharp.

1

REMOVINGA “stone hammer”was used tosharpen the edgesof the tools.

2

MAP OF LOCATIONSAND MIGRATIONS

AFRICA

ASIA

600,000 YEARS AGO 400,000 YEARS AGO 150,000 YEARS AGO 160,000 YEARS AGO 25,000 YEARS AGO

Homo heildebergensis is in Europe,part of Asia, and Africa.

Wooden spears found in Germany and theUnited Kingdom date back to this time.

Homo neanderthalensis lives in the IceAge in Europe and western Asia.

First Homo sapiensfound in Africa

Homo neanderthalensis becomesextinct from unknown causes.

46 HUMAN EVOLUTION

Descendants of Homo heidelbergensis, theNeanderthals were the first inhabitants ofEurope, western Asia, and northern Africa.

Diverse genetic studies have tried to determinewhether it is a subspecies of Homo sapiens or aseparate species. According to fossil evidence,Neanderthals were the first humans to adapt tothe extreme climate of the glacial era, to carryout funerals, and to care for sick individuals.With a brain capacity as large or larger than thatof present-day humans, Neanderthals were able todevelop tools in the style of the Mousterian culture.The cause of their extinction is still under debate.

Humans of the Ice AgeCharacterized as the caveman of the Ice Age, Homoneanderthalensis was able to use fire and diverse tools that

allowed it to work wood, skins, and stones, among other materials.They used the skins to cover themselves from cold and to buildshelter, and the stones and the wood were key materials in theweapons used for hunting. The bone structure of their fossils revealsa skull with prominent ciliary arcs, sunken eyes, a wide nose, andlarge upper teeth, probably used to grasp skins and other objectsduring the process of rudimentary manufacture.

Homo neanderthalensisThe Middle Paleolithic (400,000 to30,000 years ago) is dominated by the

development of Homo neanderthalensis. In thecontext of the Mousterian culture, researchershave found traces of the first use of caves andother shelters for refuge from the cold. Huntersby nature, H. neanderthalensis created tools anddiverse utensils, such as wooden huntingweapons with sharpened stone points.

HOMONEANDERTHALENSIS

INDIAN OCEAN

HOMOHEIDELBERGENSIS

60,000THE AGE OF SOME NEANDERTHAL

DISCOVERIES

MAN—HUNTERMales were dedicated to the search forfood, while the women looked afterchildren. It is believed that Neanderthalshunted large prey over short distances.They used wooden spears with stonepoints and probably jumped on the prey.

Rocks for cuttingand scraping

They lived in shelters made of mammothbones and covered with skins.

GravesMuch is knownabout theNeanderthalsbecause theyburied their dead.

years agoyears ago

100,000TOOLS FOUND

GREATER CRANIAL CAPACITYIn comparison to modern humans,Neanderthals had a larger brain capacity.

PHYSICAL CONTEXTThe bones in the hand made it possible to graspobjects much more strongly than modern man can.

5.4 FEET(1.65 M)

COMPARATIVESIZE

98 cubic inches (1,600 cu cm) cranial capacity

6 FEET(1.8 M)

Prominentsuperciliaryarch

Skull found in LaChapelle-aux-Saints(France)

Wide noseTo endure thehardships of theclimate


Tools fortanning hides

Able Hunters

MAP OFSITES

AFRICA

ASIA

150,000 YEARS AGO

The “Mitochondrial Eve”is the common ancestorof all people.

“Nuclear Adam” was thecommon ancestor of allthe men of the world.

Traces of Homosapiens in China

Cro-Magnon (typeof Homo sapiens)appears in Europe.

Theories of ExpansionThere is no agreement among scientistsabout how the expansion of Homo sapiens

to the entire world took place. It is believed thatthe “Mitochondrial Eve,” the most recentcommon ancestor, lived in Africa, becausethe people of that continent have greatergenetic diversity than those of the othercontinents. From there, in variousmigratory waves, Homo sapiens wouldhave reached Asia, Australia, andEurope. However, some scientists thinkthat there were no such migrations butthat modern humans evolved more orless simultaneously in variousregions of the ancient world.


Direct AncestorsT

he origin of the human species is still in debate, even though scientists have been able toestablish that H. sapiens is not directly related to the Neanderthals. The most acceptedscientific studies for dating Neanderthal fossils places the oldest specimens some 195,000

years ago in Africa. New genetic studies based on mitochondrial DNA have corroborated that dateand have also contributed to determining the possible migration routes that permitted the slowexpansion of H. sapiens to other continents. Meanwhile, the new discoveries raise unansweredquestions about what happened in the course of the 150,000 years that preceded thegreat cultural revolution that characterizes H. sapiens and that occurred some40,000 years ago with the appearance of Cro-Magnon in Europe.

The theory of regional continuity, ormultiregional evolution, states thatthe modern human developedsimultaneously in diverse regions ofthe world, like the evolution of localarchaic Homo sapiens. The lastcommon ancestor would be aprimitive Homo erectus that lived inAfrica some 1.8 million years ago.

Multiregional Evolution

Homo sapiens sapiensIt is believed that Cro-Magnon arrived in Europe some40,000 years ago. Evidence of prehistoric art,

symbolism, and ritual ceremonies distinguish this advancedculture from other species of hominins that preceded it.It was well-adapted to its environment, lived in caves, and developed techniques of hunting in groups. It captured large animals with traps and small ones with rocks.

TOOLSHomo sapiens inventedmultiple tools for varioususes and were usuallymade from stone, bone,horns, and wood.

FIRST WAVEThe modern humanswould have left Africasome 60,000 years agoand populated Asia andAustralia.

SECOND WAVEwould have arrivedsome 40,000 yearsago in central Asia,India, eastern Asia,Siberia, and, later,America.

According to this theory, modernman is an evolution of the archaicHomo sapiens that emerged inAfrica. From there it would haveextended to the rest of the world,overrunning the Neanderthals andprimitive Homo sapiens. Theanatomical differences between theraces would have occurred in thelast 40,000 years.

Out of Africa

years150,000

MITOCHONDRIAL EVE

EVOLUTION OFTHE SKULLCro-Magnon hada small face,high forehead,and longer chin.

CRANIALCAPACITYIts cranial cavitycould hold abrain of up to 97cubic inches(1,590 cu cm).

150

,00

0 y

ears

40

0,0

00

yea

rs

Homoerectus

Homoerectus

Hom

o sa

pien

s

120,000 YEARS AGO

Homo sapiens begins to extendthrough Africa.

90,000 YEARS AGO 60,000 YEARS AGO 40,000 YEARS AGO

Hom

o sa

pien

s

AMERICAOne of the finaldestinations

AFRICAN CRADLEThe majority ofpaleoanthropologistsand geneticists agreethat humans of todayemerged in Africa. It isthere they have foundthe oldest bones.

GENERAL ROUTE DATE OF MIGRATION40,000 YEARS AGO

200,000YEARS AGO

70,000-50,000YEARS AGO

50,000YEARSAGO

40,000YEARS AGO

40,000-30,000YEARS AGO

20,000-15,000YEARS AGO

15,000-12,000YEARSAGO

KEY

WÜRM GLACIATION35,000 YEARS

AURIGNACIAN30,000 YEARS AGO

PERIGORDIAN27,000 YEARS AGO

SOLUTREAN20,000-50,000 YEARS AGO

END OF PALEOLITHIC9,000 BC

The Upper Paleolithic begins. Tools of mammoth tusk,flake tools

Well-cut tools, including amultiangle graver

Use of oxide to paint, pointedinstruments

End of the glaciations, with animprovement of the global climate


Culture, the Great LeapA

lthough questions remain about how culture originated, it is almost impossible todetermine which things of the human world are natural and which are not. Scientists ofmany disciplines are trying to answer these questions from the evidence of prehistoric life

found by paleontologists. The subspecies of mammals to which man belongs, Homo sapienssapiens, appeared in Africa some 150,000 years ago, disseminated through the entire Old Worldsome 30,000 years ago (date that the oldest signs of art were found), and colonized America11,000 years ago; but the first traces of agriculture, industry, population centers, and control overnature date from barely the last 10,000 years. Some believe that the definitive leap towardculture was achieved through the acquisition of a creative language capable of expressing ideasand sentiments more advanced than the simple communication of Homo erectus.

The first artistsCave paintings, like those of the caves ofAltamira (Spain) and Lascaux (France),

leave no doubt that those who made them trulypossessed the attributes of human beings.Architecture had not arrived, but paintings had,engraved and sculptured in stone or bone. Thereexist various theories about the function of cavepainting that consider the aesthetic, themagical, the social, and the religious—not muchdifferent from the questions about art today.

Builders of objectsHomo sapiens sapiens distinguished itself from itsancestors, who were already making rudimentary tools,

through the growing use of such new materials as bone andabove all for the specialization of new tools. Mortars, knives,boring tools, and axes had forms and functions continuallymore sophisticated. There also appeared, in addition to utensilsand tools, objects with ornamental and representativefunctions that attested to humans' increasing capacity forsymbolism. These manifestations, through which the art couldleave the caves, are known as portable art. It produced objectsthat were utilitarian, luxurious, or ceremonial, like thePaleolithic “Venus” figurines.

SPEARThey representedinstruments that theyused at that time.

LAURELS ANDSPIKESForms reproducedeven in tools

CAVE-PAINTING TECHNIQUES

SYMBOLISMThe “Venus of Willendorf”measures 4 inches (11 cm)in height and was found inAustria.

TWO-SIDED KNIFEIts invention presagedthe most importantcultural revolution of theUpper Paleolithic.

COLORSThe pigments used were of naturalorigin, such as vegetable charcoal, redocher, and brown ocher.

HUNTING SCENES INTHE CAVE OF TASSILI-N-AJJER, ALGERIA

“HORSE” PAINTEDIN LASCAUX IN THEPALEOLITHIC HANDS IMPRINTED AS A

NEGATIVE APPEAR INMULTIPLE PLACES.

years old 24,000IS THIS LITTLE STATUE

years old 14,000THE PAINTINGS OFALTAMIRA

ART ON THE WALLS

Cave painting is a phenomenon that was found mainlyin the current regions of France and Spain. In France,there are more than 130 caves; the most famous arelocated in the Aquitaine region (Lascaux, Pech-Merle, Laugerie, La Madeleine) and in thePyrenees (Niaux, Le Tucs d'Audubert,Bedeilhac). Spain has some 60 caves in theCantabria region to the north, amongthem the cave of Altamira, and 180caves farther south. Examples fromother regions include caves atAddaura, Italy, and Kapova, Russia.Portable art, on the other hand,was abundant in all Europe.

Sites in Europe wherePaleolithic art hasbeen found

MEDITERRANEAN SEA

CASPIAN SEA

EUROPE

PREGNANTANIMALSA recurring theme incave paintings

MICROCEPHALYThe head is small inrelation to the rest ofthe animal's body.

OTHER THEMESAND MOTIVES

OCHER BLACK

HARPOONThis complexinstrument ofbone dates fromsome 11,000years ago(MagdalenianPeriod, France).

POLISHED AXFound in Wetzlar,Germany, it showsthe polishingtechnique of 20,000years ago.

PALEOLITHIC TOOLS

GEOMETRIC DESIGNSDotted and linealgeometric designs,along with mythicalchimeras, have beenfound amongEuropean cavepaintings similar tothe rock art ofAboriginalAustralians.

BLOWINGOne techniqueconsisted ofblowing pigmentthrough a rod orhollow bone.

MAGDALENIAN15,000 YEARS AGO

The greatest flourishing of caveart in southern Europe

8000 BC 7000 BC

First indications ofagricultural activities

Expansion of agriculture.Complex funerary rites.

Stable settlements in thePersian Gulf

Invention of writing inMesopotamia

First vehicles withwheels in Asia.


CROPS In the fields near ÇatalHüyük, the inhabitants grewwheat, sorghum, peas, andlentils. They gathered apples,pistachios, and almonds.

LOCATION OFÇATAL HÜYÜK

Urban RevolutionS

ome 10,000 years ago, there was an interglacial period on Earth thatcaused a gradual increase in temperatures and an overall climaticchange that brought a modification to the life of humans. Instead

of roaming from place to place to hunt, people began to createsocieties based on sedentary life, agriculture, and the domestication ofanimals. Some villages grew so much that they became true cities,such as Çatal Hüyük in southern Turkey. In the ruins of this city,considered one of the milestones of modern archaeology, were founda good number of ceramics and statues of the so-called mothergoddess—a woman giving birth—that belonged to a fertility ritual.In addition, there are signs that the inhabitants practiced funeralrights and built dolmens for collective graves.

CULTSThere is a direct relationship betweenthe emergence of agriculture and thecult of the feminine because of theimportance of fertility. Statuettes ofpregnant women were found inhomes in shrines decorated withmolded bull heads and other figures.

Country

Year

Type ofCity

Turkey

7000 BC

Farming-livestock

LENTILS APPLES WHEAT

MOTHERGODDESS

WAS ONE OF THEFIRST CITIES.

6,000ÇATAL HÜYÜKyears BC

The Neolithic City ofÇatal Hüyük

Çatal Hüyük is located in southernAnatolia (Turkey). Houses were built side

by side, sharing a common wall. There were noexterior windows or openings, and the buildingshad flat-terraced roofs. People entered throughthe roof, and there were usually one or twostories. The walls and terraces were made ofplaster and then painted red. In some mainresidences, there were paintings on the wallsand roof. The houses were made of mud bricksand had a sanctuary dedicated to the mothergoddess. During the excavation, many religiousarticles were uncovered: the majority wereceramic figures in relief depicting the mothergoddess and heads of bulls and leopards.

270squarefeet(25 sq m) WAS THE AVERAGESIZE OF A HOUSE

OVEN

ELEVATEDPLATFORM

OPENHEARTH

ALTARPLATFORM

ALTARWITH BULL

HORNS

BULL'S HEADWITH HORNS

AD 320 3500 BC6000 BC

1 2 3 4

OTHER TYPES OF CONSTRUCTIONThe process of carrying out a megalithic construction began in a quarry, where large blocks of stone were extracted.

TransportThe stones were transportedon rollers to the place chosenfor the erection of themonument.

ErectionThe blocks were dropped intoa hole and placed in a verticalposition.

EarthworksEmbankments weremade for theconstruction of a dolmen.

TrilithThe horizontal block wastransported over an embankmentand placed on the two uprightstones.

CITY OF ÇATAL HÜYÜK

TRANSCRIPTION OF THE GENETIC CODE 62-63

THE PATH OF THE GENE 64-65

PROBLEMS OF HEREDITY 66-67

The cells of the body areconstantly dividing to replacedamaged cells. Before a celldivides to create new cells, aprocess known as mitosis, or

to form ovules or spermatozoa, aprocess called meiosis, the DNAincluded in each cell needs to copy, orreplicate, itself. This process is possiblebecause the DNA strands can open and

separate. Each of the two strands of theoriginal DNA serves as a model for anew strand. In this chapter, we will alsotell you how human beings vary inheight, weight, skin color, eyes, and

other physical characteristics despitebelonging to the same species. Thesecret is in the genes, and we will showit to you in a simple way.

SELF-COPYING 56-57

THE CHROMOSOME 58-59

THE REPLICATION OF LIFE 60-61

Mechanisms of Heredity DNAComplex macromoleculethat contains a chemicalcode for all the informationnecessary for life

EVOLUTION AND GENETICS 5756 MECHANISMS OF HEREDITY

Self-CopyingA

ll living organisms utilize cellular division asa mechanism for reproduction or growth.The cellular cycle has a phase called the S

phase in which the duplication of the hereditarymaterial, or DNA, occurs. In this phase, twoidentical sister chromatids are united into onechromosome. Once this phase of duplication isfinalized, the original and the duplicate willform the structures necessary for mitosisand, in addition, give a signal for the wholeprocess of cellular division to start.

The nucleus is the control center of the cell.Generally it is the most noticeable structure

of the cell. Within it are found the chromosomes,which are formed by DNA. In human beings,each cellular nucleus is composed of 23 pairsof chromosomes. The nucleus issurrounded by a porous membrane madeup of two layers.

The Cellular Nucleus

History of the Chromosome

The chromosomes carry the genetic informationthat controls the characteristics of a human being,

which are passed from the parents to the children andfrom generation to generation. They were discovered byKarl Wilhelm von Nägeli in 1842. In 1910 Thomas HuntMorgan discovered the primordial function of thechromosomes: he called them carriers of genes. Thanks todemonstrating this, Morgan received the Nobel Prize forPhysiology or Medicine in 1933.

HOW THEY LOOK

Once they have duplicated, thechromosomes form a structure inthe shape of a cross. In thisstructure, the centromere functions asthe point of union for the chromatids.

GROWTH ANDCELLULAR DIVISION

The cellular cycleincludes cellgrowth, in whichthe cell increases inmass and duplicatesits organelles, andcell division, inwhich DNA isreplicated and thenuclei divide.

AMOUNT OFCHROMOSOMESACCORDING TO SPECIES

The number of chromosomes of aspecies varies independently of itssize and complexity. A fern hasthousands of chromosomes and afly only a few pairs.

CYTOKINESISThe cytoplasm of the mothercell divides and gives rise totwo daughter cells identicalto the mother.

MITOSISThe two sets ofchromosomes are distributed,one set for each nucleus ofthe two daughter cells.

S PHASEThe DNA and associatedproteins are copied, resultingin two copies of the geneticinformation.

PHASE G2The chromosomes begin tocondense. The cell preparesfor division.

6.5 feet(2 m)LENGTH OF DNA INHUMAN CELLCHROMOSOMES

8INTERPHASE

2

34

5

FRUIT FLY

chromosomes

46HUMAN BEING

chromosomes

24SALAMANDER

chromosomes1,262FERNS

chromosomes

PHASE G1The cell doubles in size. Thenumber of organelles, enzymes,and other molecules increases.

1


The ChromosomeT

he chromosome is a structural unit that consists of a molecule of DNAassociated with proteins. Eukaryote chromosomes condense duringmitosis and meiosis and form structures visible through a microscope.

They are made of DNA (deoxyribonucleic acid), RNA (ribonucleic acid), andproteins. The majority of the proteins are histones, small positively chargedmolecules. Chromosomes carry the genes, the functional structuresresponsible for the characteristics of each individual.

Carrier of GenesIn the DNA, certain segments of the molecule arecalled genes. These segments have the genetic

information that will determine the characteristics of anindividual or will permit the synthesis of a certain protein.The information necessary for generating the entire organismis found in each cell, but only the part of the informationnecessary for reproducing this specific type of cell isactivated. The reading and transmission of the informationfor use outside the nucleus is performed by messenger RNA.

KaryotypeThe ordering and systematic classification ofthe chromosomes by pairs, size, and positionof the centromere. The chromosomesthat are seen in a karyotype arefound in the metaphase ofmitosis. Each one of themconsists of two sisterchromatids united bytheir centromeres.

THE FRAMEWORKEach one of the rosettesconsists of loopsstabilized by the“scaffolding” of otherproteins. Theseloops help tocondense thechromatin.

2

NUCLEOSOMEA group of eight histonemolecules with two DNAspirals twisted aroundthem. The “tails” of thehistones seem to interactwith the molecules thatregulate genetic activity.

4

PROKARYOTE CELLProkaryote cells do not have acellular nucleus, so the DNA is foundin the cytoplasm. The size of the DNAdiffers according to species.Prokaryotes are almost all unicellularorganisms belonging to the domainsof the archaea and bacteria.

CIRCULARCHROMOSOME

OF BACTERIA

NITROGENBASES

SPACER DNAThe nucleosomes areunited by chains ofbase pairs of DNA0.0000004 inch(0.00001 mm) long.

PEARL NECKLACEIf the DNA chain is stretchedand observed under amicroscope, it resemblesbeads on a string.Nevertheless, DNA chains aregenerally found pressed verytightly around the nucleus.

0.0000012 inch(0.00003 mm)DIAMETER OF EACH SOLENOID

SOLENOIDA group of sixnucleosomes thatform each turninside the loops

3

1CHROMATINS

There are two types:euchromatin, lightly

packed, andheterochromatin, more

densely packed. Themajority of nuclear

chromatin consists ofeuchromatin. 30

IN EACH TURN OFTHE SPIRAL

rosettes 60THE AMOUNT OFDNA BETWEENNUCLEOSOMES

base pairs

6IN EACH TURN

nucleosomes

6IN EACH ROSETTE

loops


The Replication of LifeI

n deoxyribonucleic acid—DNA—all the genetic informationof a complete organism is found. It has complete control ofheredity. A DNA molecule consists of two strands of

relatively simple compounds called nucleotides. Eachnucleotide consists of a phosphate, sugar, and one offour kinds of nitrogenous bases. The nucleotides oneach strand are paired in specific combinations andconnected to each other by hydrogen bonds. Thetwo strands coil around each other in the form of aspiral, or double helix.

Complementary.

Various specialized proteins called enzymes act asbiological catalysts, accelerating the reactions of

replication: helicase, which is in charge of opening thedouble helix of DNA; polymerase, which is in charge ofsynthesizing the new strands of DNA in one direction; andligase, which seals and joins the fragments of DNA thatwere synthesized.

REPLICATIONThe genetic information is encodedin the sequence of the bases ofthe DNA nucleotides aligned alongthe DNA molecule. The specificityof the pairing of these bases is thekey to the replication of DNA.There are only two possiblecombinations—thymine withadenine and guanine withcytosine—to form thecomplementary links of the strandsthat make up the DNA chain.

NucleotidesThe nucleotides have three subunits: aphosphate group, a five-carbon sugar, and anitrogenous base. In DNA these bases aresmall organic molecules. Adenine and guanineare purines, and cytosine and thymine arepyrimidines, smaller than the purines. Allare composed of nitrogen, hydrogen,carbon, and oxygen—except for adenine,which has no oxygen. The adenine isalways paired with thymine andguanine with cytosine. The first pair isjoined by two hydrogen bonds and thesecond by three.

ADENINE

GUANINE

CYTOSINE

HYDROGENBOND

THYMINE

NEWCHAIN

ORIGINALCHAIN

Biological RevolutionDeciphering the molecular structure of DNAwas the major triumph of biomolecular studiesin biology. Based on work by Rosalind Franklinon the diffraction of X-rays by DNA, JamesWatson and Francis Crick demonstrated thedouble-helix composition of DNA in 1953and for their work won the 1962 NobelPrize for Physiology or Medicine.

WEAK BRIDGESHelicase separates thedouble helix, thusinitiating the replication ofboth chains. The chainsserve as a model to makea new double helix.

BASICMECHANISMThe new bases jointo make a DNAchain that is adaughter of theprevious model.

1

FREED ENERGYThe energy to form new links isobtained from the phosphategroups. The free nitrogenous basesare found in the form oftriphosphates. The separation ofthe phosphates provides theenergy to interlace the nucleotidesin the new chain that is being built.

2NEW CONNECTIONThe new chains of DNAcouple in shortsegments, and the ligasejoins them to form thedaughter molecules.

3PERFECT REPLICATIONThe result is two new molecules, each withone strand from the original DNA and onenew complementary strand. This is calledsemiconservative replication. The geneticinformation of the newstrand is identical tothat of the originalDNA molecule.

4

50PER SECOND IS THE SPEED OF DNAREPLICATION IN HUMANS.

nucleotides

ORIGINALCOPY

Transcription ofthe Genetic Code

This complex process of translation allows theinformation stored in nuclear DNA to arrive at theorganelles of the cell to conduct the synthesis of

polypeptides. RNA (ribonucleic acid) is key to this process.The mRNA (messenger RNA) is in charge of carryinginformation transcribed from the nucleus as a simple chainof bases to the ribosome. The ribosome, together withtransfer RNA (tRNA), translates the mRNA and assemblessurrounding amino acids following the genetic instructions.

SEPARATION OF DNAWhen the DNA is to betranscribed, its double chainseparates, leaving asequence of DNA bases freeto be newly matched.

1

TRANSCRIPTIONOne of the chains, called thetranscriptor, is replicated by theaddition of free bases in thenucleus through the action of anenzyme called RNA polymerase.The result is a simple chain ofmRNA (messenger RNA).

2

LEAVING THE NUCLEUSIf the DNA were to leave thenucleus, it would get corrupted,so it is the mRNA thattranscribes the DNA'sinformation in a simple chain,which takes the information tothe cytoplasm of the cell.

3

INTERRUPTIONThe synthesis is producedbetween the start codon and thestop codon. Once the chainreaches the stopping point, theribosome stops synthesizing thepolypeptide, and the ribosomereleases the polypeptide.

5

TRANSLATIONIn the ribosome thetranslation of themRNA to synthesizethe polypeptide isinitiated with theparticipation of tRNA.

4

SYNTHESIS OFPOLYPEPTIDESThe polypeptides form when a group of aminoacids unite in a chain. For this to happen, theribosome: translates the information that themRNA transcribed from the nuclear DNA;codifies the amino acids and their order withthe help of tRNA, through the matching ofcodons and anticodons; and places each aminoacid exactly where it belongs.

ENZYMEScollaborate in theformation of thepolypeptide chain bymaking the peptidechains that join theamino acids.

POLYPEPTIDESare formations of about10 to 50 amino acids.Each amino acid isconsidered a peptide.

tRNATransfer RNA is in charge ofrecognizing and translating theinformation that the mRNAcontains.

RIBOSOMEThe cellular organelle wherethe synthesis of polypeptidesoccurs. It helps translate theinformation brought by themRNA.

COMPRESSION OF RNAIn the formation of mRNA,useless parts are eliminatedto reduce its size.

DNA RNA MATURE RNA

DNA TRANSCRIPTIONThe process of copying one simple chain ofDNA is called transcription. For it to happen,the double strands separate through theaction of an enzyme, permitting the enzymeRNA polymerase to connect to one of thestrands. Then, using the DNA strand as amodel, the enzyme begins synthesizingmessenger RNA from the free nitrogenousbases that are found inside the nucleus.


With introns

ANTICODON

Withoutintrons

30ARE COPIED DURING THEPROCESS OF TRANSCRIPTION.

bases per second

2METAPHASE IThe nuclear membranedisappears. Thechiasmata, composedof two chromosomes,align, and thecentromeres moveaway.

3ANAPHASE IThe chiasmata separate. Thechromosomes separate fromtheir homologues toincorporate themselves into thenucleus of the daughter cell.

4TELOPHASE IThe nuclear membranesreform, and the number ofchromosomes enclosed in eachhas been reduced by half.

5PROPHASE IIThe division of the new daughtercells begins: the chromatidscondense; the nuclear membranesdisintegrate; and the spindles form.

6METAPHASE IIcontinues in the daughter cells. Thechromosomes align at their middle,and the chromatids affix themselvesto the fibers of the spindle.

7ANAPHASE IIThe centromeres divideagain, and the sisterchromatids divide, goingto opposite poles.

8NUCLEUS OFTELOPHASEThe spindle disappearsand forms a membranearound each nucleus.

9NEW NUCLEIThe new formations havea haploid endowment ofchromosomes.

10CYTOKINESISThe cytoplasm divides, separating themother cell into two daughter cells.


The Path of the GeneS

exual differences in the heredity of traits constitute a model knownas sex-linked inheritance. The father of genetics was Gregor Mendel.He established the principle of independent segregation, which is

possible only when the genes are situated on different chromosomes; ifthe genes are found on the same chromosome, they are linked, tending tobe inherited together. Later Thomas Morgan contributed more evidence ofsex-linked inheritance. Today many traits are identified in this model, suchas hemophilia and color blindness.

MEIOSIS IIIn the second division, the two chromatids that form eachchromosome from meiosis I are separated. As a result ofthis double division, four daughter cells are produced thatcontain half the characteristic chromosomal number—i.e.,23 chromosomes each (haploid cells). Each chromosome will

be composed of a chromatid.

B

MEIOSIS IThis first division has four phases,of which prophase 1 is the mostcharacteristic of meiosis, since itencompasses its fundamentalprocesses—pairing and crossingover, which allow the number ofchromosomes by the end of thisprocess to be reduced by half.

A

HEREDITY

In human beings, some genes have beenidentified that are found in theheterochromosomes and deal with sexlinkage. For example, the genes thatcode for hemophilia and color blindnessare found in the heterochromosome X.

(1822-84)

Gregor MendelPOSTULATED THE FIRSTLAWS OF INHERITANCE.

1920THOMAS MORGAN studied the color of eyes in thefly Drosophilia melangaster.

1PROPHASE IThe homologouschromosomes pairup, formingchiasmata, which areunique to meiosis.

C

CHROMOSOMESDIFFERENTIATEDBY THEIR GENES

A

Crossing OverProcess in which apair of analogouschromosomesexchange materialwhile they are joined

INFORMATIONCROSSING OVER

B

CENTROMERED

LinkageThe genes,arranged inlinear form andon the samechromosome, areinherited asisolated units. CHROMOSOME

FROM THE MOTHER

CHROMOSOMEFROM THE FATHER

Linkedgenes

Gene

RESULTING PAIR OFCHROMOSOMES

POSSIBLECOMBINATIONS

TALLSTEM

SHORTSTEM

Mendel's first law, orprinciple, about heredityproposes that by crossingtwo homozygous parents(P), dominant and recessivefor the same trait, itsdescendant, or filial 1 (F1),will be uniform. That is, allthose F1 individuals will beidentical for the homozygousdominant trait. In thisexample using the trait seedcolor, yellow is dominant andgreen is recessive. Thus, theF1 generation will be yellow.

Uniformity

The first law, known as the law ofsegregation, comes from the resultsobtained with the crosses made withF1 individuals. At the reappearance ofthe color green in the descendants, orfilial 2 (F2) generation, he deducedthat the trait seed color is representedthrough variants, or alleles, that codefor yellow (dominant color) and green(recessive color).

Traits andAlleles

The legacy of Mendelmolecular genetics developed. Thisscience studies heredity on a molecularlevel and analyzes how the structure ofDNA and its functional units, or genes,are responsible for heredity. Moleculargenetics links classical genetics andmolecular biology. Its use allows us toknow the relationship that existsbetween visible traits and the molecularhereditary information.

The principles proposed by Mendelare the basis of classical, or

Mendelian, genetics, which reached itspeak at the beginning of the 20thcentury. This science studies how thevariants, or alleles, for a morphologicaltrait are transmitted from one generationto the next. Later, after confirmation thatthe components of the nucleus are thosein charge of controlling heredity,


Toward the end of the 19th century, the formin which the physical traits of parents weretransmitted to their offspring was uncertain.

This uncertainty extended to the breeding of plantsand animals, which posed a problem for agricultureand livestock producers. In their fields they sowedplants and raised animals without knowing whatthe quality of their products would be. The work ofGregor Mendel and his contributions to moleculargenetics eventually led to a solution to theseproblems and to an understanding of how themechanisms of heredity work.

Problemsof Heredity

PP

F1

The man who calculatedGregor Johann Mendel was born in Heinzendorf,Austria, in 1822 and died in the city of Brünn,

Austria-Hungary (now Brno, Czech Republic) in 1884.He was a monk of the Augustinian order who at theUniversity of Vienna pursued, over three years, differentstudies in mathematics, physics, and naturalsciences. This ample academic training and hisgreat intellectual capacity permitted himto develop a series of experiments inwhich he used pea plants (Pisumsativum). He analyzed varioustraits, among them theappearance of flowers, fruits,stems, and leaves. In hismethodology, he included aninnovation: he submitted hisresults to mathematicalcalculations. Hisconclusions were key tounderstanding themechanism ofheredity.

PURE INDIVIDUALSMendel used pureindividuals, plantsthat he knew were

homozygous dominant andrecessive for a specific trait.For his experiments, Mendelcarefully covered or directlycut the stamens of theflowers to prevent themfrom self-fertilizing.

CROSSING

OBTAINING THE FIRSTFILIAL GENERATION

F2OBTAINING THE SECOND

FILIAL GENERATION

SELF-FERTILIZATION

IndependenceThe second law, called the law ofindependent assortment, proposesthat the alleles of different traits aretransmitted independently to thedescendant. This can be demonstratedby analyzing the results of theexperiments in which Mendelexamined simultaneously the heredityof two traits. For example, he analyzedthe traits “color and surface texture ofseeds.” He took as dominant allelesthose for yellow and a smooth surfaceand as recessive the alleles for greenand a wrinkled surface. Later hecrossed pure plants with bothcharacteristics and obtained theF1 generation that exhibitedonly dominant alleles. The self-fertilization of the F1generation produced F2individuals in theconstant proportion9:3:3:1, showing thatcombinations ofalleles weretransmitted in anindependentmanner.

Yellow

Yellow Yellow

Green

1

INSEMINATIONOnce self-fertilization wasimpeded, Mendel

inseminated the pollen of ahomozygous dominant onan ovary of a homozygousrecessive and vice versa. Inaddition to color, heanalyzed other traits, suchas length of stem,appearance of seeds, andcolor of flowers.

2

FRUITFUL WORK

When the plantsproduced legumes,the seeds exhibited

determined colors. Uponcarrying out his experimentson hundreds of individuals, heobtained much information.The monk recorded the data intables and submitted them toprobability analysis. In thisway Mendel synthesized hisresults into the conclusionsthat we know today as theMendelian laws, or principles,of inheritance.

3

Yellow: 3Green: 1The cross, or self-fertilization, of individualsof the F1 generation produces F2 individualswith yellow and green seeds in constant 3:1ratio. In addition, it is deduced that theF1 generation is made up ofheterozygous individuals.

GREEN The green seedsappear in lower proportionthan the yellow.

BOTANY This display is a botanical teaching tool. Analtruistic naturalist, Mendel dedicated himself to conservingin herbariums the specimens of different species of plants.

IN BETWEENIn certain cases, thecolor of the eyes does notrespond to a completedominance. It is determined by theinfluence of alleles of other genes.

PEAS The pea plants of thePisum sativum species werekey for the conclusions obtainedby Mendel about heredity.

1

3

3

3

1

9

During the 19th century, thegardens of the Abbey of SaintThomas were the laboratorythat Mendel used for hisexperiments on heredity.During the 20th century,classical genetics andmolecular genetics amplifiedour knowledge about themechanism of heredity.

1869The Austrian Augustinianmonk Gregor Mendelproposes the laws thatexplain the mechanisms ofheredity. His proposal isignored by scientists.

1869Johann Friedrich Miescher,a Swiss doctor, suggeststhat deoxyribonucleic acid,or DNA, is responsible forthe transmission ofhereditary traits.

1889Wilhelm von Waldeyergives the name“chromosomes” to thestructures that formcellular DNA.

1900The German Carl ErichCorrens, the Austrian ErichTschermak, and theDutchman Hugo de Vriesdiscover, independently, theworks of Mendel.

1926T.H. Morgan demonstratesthat the genes are foundunited in different groupsof linkages in thechromosomes.

1953James Watson and FrancisCrick propose a double-helix polymer model for thestructure of DNA.

1973Investigators produce thefirst genetically modifiedbacteria.

1977North American scientistsfor the first time introducegenetic material fromhuman cells into bacteria.

1982The United Statescommercializesrecombinant insulinproduced by means ofgenetic engineering.

1990An international publicconsortium initiates theproject to decipher thehuman genome.

1997Dolly the sheep is the firstcloned mammal.

2000The Human Genome Projectand the company Celerapublish the decipheredhuman genome.

FROM THE GARDEN

HOMOZYGOUS OR HETEROZYGOUSBrown color of the eyes ispresent in individualswith at least onedominantallele.

HOMOZYGOUS RECESSIVEBlue color of the eyes is

present in individualswith two recessive

alleles.

DOMINANTWith twodominant alleles,the individual ishomozygousdominant for thistrait.

HOMOZYGOUSWith tworecessive alleles,the individual ishomozygousrecessive for thistrait.

HETEROZYGOUSWhen there is anallele of eachtype, theindividual isheterozygous forthis trait.

The traits of a gene in an individual are expressed according to a pairof variants, or alleles. In general, the dominant alleles are expressedeven though there may be another allele for the same gene. A recessiveallele is expressed only if it is the only allele present in the pair.

DOMINANT ANDRECESSIVE

The Age ofGenetics

DNA analysis has become acommon practice indiagnosing and predictinggenetically inherited diseases.It is also highly useful in

forensic procedures. The DNA sequence,like fingerprints, is unique to eachindividual. In these pages you will learnabout achievements in the field ofgenetically modified foods and animals,

the latest advances in genetic medicine,and future applications of stem cells.According to specialists, these cellscould be used to regenerate damagedtissues or organs. Another technique that

will surely provide a definitive cure forserious diseases will involve exchangingdefective genes for healthy ones.

COW CLONING 78-79

BIOCHIP APPLICATIONS 80-81

GENE THERAPY 82-83

DNA FOOTPRINTS 84-85

GENETIC SOLUTION 70-71

DNA MARKERS 72-73

GENOME IN SIGHT! 74-75

STEM CELLS 76-77

DNA ANALYSISGenetic identification is a nearlyinfallible proof of identity used incases of disappearance, rape,murder, and paternity suits.

MODIFIED FOODS 86-87

PHARMACEUTICAL FARMS 88-89

THE GENETIC ANCESTOR 90-91

BACTERIALPLASMID

First CaseInsulin was the first proteinproduced by geneticengineering. It was approvedfor human use in 1982.

recombinantantibiotics and

vaccines

UnionThe human and bacterial DNAjoin at their free ends and forma recombined plasmid.This plasmid containsthe humaninsulin gene.

Insertion A culture of nonpathogenic receptorbacteria is placed in a solution thatcontains the recombined plasmid. Thesolution is then subjected to chemicaland electrical stimuli to incorporate theplasmid that contains the insulin gene.

3

ReproductionThe bacteria reproduce constantly infermentation tanks with water andessential nutrients. In these conditions,the recombined bacteria transcribe theinformation in their chromosomes toproduce proteins. The bacteria also readthe information from the human DNAthat was inserted using the recombinedplasmid, and they produce insulin.

4

INSULIN GENEThe DNAsequences forproducing insulinare insertedseparately intodifferent plasmids.

FormulationThe recombinant human insulin ischemically modified. This produces astable, aseptic compound that can beadministered therapeutically via injection.

7

ARE ALSO PRODUCED BYGENETIC ENGINEERING.

HUMAN CELLEach body cell has geneticinformation distributedamong the genes in thenucleus.

10HOURS

are needed forthe culture

population todouble.

BACTERIA Escherichia coli contain plasmids (DNAmolecules that are separatefrom chromosomal DNA).

BEFORECENTRIFUGATION

AFTERCENTRIFUGATION

Insulin inbacterialbatch

Theseparatedmaterialthatcontainsbacterialremains.

Insulinpellet

Genetic engineering applies technologies for manipulatingand transferring DNA between separate organisms. Itenables the improvement of animal and plant species,

the correction of defective genes, and the production of manyuseful compounds. For example, some microorganisms aregenetically modified to manufacture human proteins, whichare vital for those who do not produce them efficiently.

Genetic Solution

RECOMBINEDPLASMID WITH

HUMAN DNA

ExtractionDNA is extracted from a human cell toobtain the gene that codes for producinginsulin. The DNA is cut using restrictionenzymes that recognize the points wherethe gene in question begins and ends.These enzymes also cut the bacterialplasmid. The DNA fragments thus obtainedhave irregular and complementary ends.

1

PurificationThe culture is circulated at highpressure through tiny tubes thatdestroy the bacteria. The solutioncontains a large amount of insulinthat must be separated from theother proteins in the solution.

5

CentrifugationCentrifuges separate the variouscompounds present in the solution fromthe bacterial remains and the humaninsulin. The proteins present in the solidmatter are separated from the originalsolution.

6

NUCLEUS

RECOMBINANTDNAThe recombinedplasmid is insertedinto the receptorbacteria.

INSERTION INTO THECHROMOSOMEThe recombined plasmidis inserted into thebacteria's chromosome.

TINYTUBE

CELLULARREMAINS

GLASSTUBES

EXTRA DNAThe plasmids maycontain up to 250,000nitrogenous basesoutside the chromosome.

MODEL ORGANISMSBesides E. coli,eukaryote cells suchas yeast are used.

Genetic EngineeringGenetic recombination consists ofintegrating DNA from different

organisms. For example, a plasmid is usedto insert a known portion of human DNAinto the DNA of bacteria. The bacteriathen incorporate new genetic informationinto their chromosomes. When their ownDNA is transcribed, the new DNA istranscribed as well. Thus, the bacteriaformulate both their own proteins andforeign proteins, such as human insulin.

INSULINPROTEIN

INSULIN

DECANTATIONThe centrifuges reducethe amount of timenecessary to separatethe solid matter.

CENTRIFUGALFORCECentrifugal forceaccelerates thedecantation.

HIGHPRESSURE

BACTERIA In phase ofexponentialgrowth. Fromnow on, theywill producethe hormoneinsulin.

ROUNDCHROMOSOME

NEW INSULINThe transcription ofhuman DNA enablesthe formation ofrecombined humaninsulin.

BACTERIALPLASMID

70 THE AGE OF GENETICS EVOLUTION AND GENETICS 71

2

In the past, individual plants in agriculture werechosen for reproduction according to visiblecharacteristics or markers, such as the shape and

color of fruit. Genetics demonstrated that thesecharacteristics come from the expression of genes. Thegenes can also be accompanied by repeating groups ofbases called DNA markers. These markers are usefulprimarily during the early phases of a plant'sdevelopment to detect whether it has a certain trait.

DNA Markers

ExtractionMolecular markers are extractedfrom DNA taken from a tissuesample. In the case of plants, evena tiny leaf may give enough DNA.

1MicrosatellitesDNA has different types ofmolecular markers. Some of

the most useful markers are calledmicrosatellites. These markers aregroups of up to 10 DNA bases thatare repeated in short sequences.Microsatellites are very useful inevaluating plant and animalpopulations. For example, the lengthof a microsatellite shows whethergiven plants of the same species arehomozygous or heterozygous for acertain trait. DNA markers areespecially useful because they arenot affected by theenvironment.

PreparationRestriction enzymes are used to snip portions of DNA that havethe microsatellite. After the microsatellite is isolated, it ismultiplied into thousands of identical units using a process calledpolymerase chain reaction (PCR). This process is carried out witheach of the samples obtained from different individuals to becompared. For example, comparing microsatellites from differenttomato plants can show which individuals are heterozygotic orhomozygotic or recessive or dominant for specific traits.

2 ElectrophoresisOnce the microsatellite samples areplaced in the polyacrylamide gel, thegel is subjected to electrophoresis. Thistechnique is widely used to separatemolecules, in this case microsatellites,with a negative electrical charge byapplying a current of electrons. Whenan electrical field is generated,electricity moves the microsatellitesthrough the gel at different speeds.Their movement varies with the ratio ofthe electrical charge to the mass ofeach microsatellite. The lightermicrosatellites travel farther than thelonger ones.

3

MICROPIPETTEThis instrument isused to insert anexact amount ofthe DNA sample.

DNA SAMPLESamples containingmicrosatellites and asubstance that glowsin UV light arescattered in a pocketof polyacrylamide gel.

ResultsAfter electrophoresis is finished,the results can be examined byexposing the gel to ultraviolet light. Thelocation of each microsatellite shows therelationship between the various samplesanalyzed. In this case, the samples show

which alleles are present and which are not.

4

YELLOWLARGEThe dominantallele isexpressed.

REDSMALLThis new traitmay be ofinterest in anew crop.

REDLARGETherecessiveallele isexpressed.

SAMPLE 1 SAMPLE 2 SAMPLE 3

POLYACRYLAMIDEGEL

GA GA GAGA GA GAMicrosatelliteof a dominanthomozygote.

GA GA GAGA GAMicrosatellite ofa heterozygoticindividual

GA GA GA GA Microsatelliteof a recessivehomozygote

MOLECULAR MARKERRepetitive sequence of a pairof bases (guanine [G] andadenine [A] in this example)

Based on MendelThe Mendelian laws, essential to thedevelopment of the field of genetics, werediscovered based on the markers of visibletraits. These traits are very useful, exceptfor a few disadvantages: they are based onan individual's phenotype (appearance),which is influenced by the environment. Inaddition, it is necessary to wait until aspecimen is fully grown in order to find outwhether it has a desired trait.

NUMBER OF SAMPLESMore than 50 DNAsamples can be placedfor comparison in thesame gel.

ELECTRICCURRENTThe positiveelectrical chargeattracts the negativecharges in the gel.

KbpThe unit ofDNA molecularlength

A MATCHThese microsatellitesmatch. This showsthat samples 2 and 3share this allele.

PARENT 1 PARENT 2

F 1

Sample 1 Sample 2 Sample 3


PolymorphismVariations in the sequence of a segment ofDNA among the individuals of a population.For example, the variations in the color oftomatoes are a result of polymorphism.

Genetic dictionaryThe 46 human chromosomes, together withmitochondrial DNA, contain all a human being's

genetic information. Knowing the location and functionof each gene or group of genes is useful for severalreasons. It enables us to know if an illness stems froma defect in a gene or group of genes and even tocorrect the illness through gene therapy. We can alsobetter understand any potential interaction among

genes that are near each other in a chromosomeand the effects of that interaction. Studying the

human genome can even reveal the origin ofour species among the primates.

1900

Gregor Mendel isrediscovered byTschermak, DeVries, and Correns.

EVOLUTION AND GENETICS 7574 THE AGE OF GENETICS

Genome in Sight!O

ne of the most far-reaching and extraordinary scientificachievements is the deciphering of the human genome. This is thecomplete set of hereditary information contained in the DNA of

human chromosomes. In less than 20 years, with a combination oforiginal genetic techniques and the power of computers, scientistsglimpsed the location of all the genes, including those that determine eyecolor, hair type, blood type, and even a person's sex.

12

34

5 6 78 9

1011

1213

14

1516

17

18

19

20

21

22

X

Y

Gau

cher

's d

isea

se

EARTHWORM P ArmShortest portion ofthe chromosome

CentromereNarrowestpoint

19,000genes

FLY

13,000genes

PLANT

25,000genes30,000

genes

HUMAN

Drosophila melanogaster, thefruit fly, is the subject ofexperiments by T.H. Morganbased on chromosomal theory.

James Watson andFrancis Crickpropose a structuralmodel of DNA.

1911 1953

Discovery thatthe humanspecies has 46chromosomes

1955

The firstdescription ofa restrictionenzyme

1968

John Gurdon firstused somatic nucleito create clones ofan amphibian larva.

1974

F. Sanger develops atechnique fordeciphering the sequenceof bases in DNA.

1975

The firsttransgenic ratsand insectsare obtained.

1981

Kary Mullis createsthe polymerasechain reactiontechnique.

1983

A plan is proposedto finish sequencingDNA in the humangenome project.

1993 1994

The genomesequencing of theCaenorhabditis

elegans nematodeis completed.

1998

The magazines Scienceand Nature publish thecomplete sequence ofthe human genome.

2003

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AUTOSOMESare the 22 pairsof humanchromosomes,excluding the sexchromosomes.

SEXCHROMOSOMES

WOMENhave a pair ofthe same sexchromosome,called XX.

MENhave achromosomepair made up oftwo differentchromosomes,X and Y.

Q ArmLongestportion of thechromosome

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Sanger MethodFrederick Sanger, an English biochemist,devised an extraordinary method fordeciphering the human genome byidentifying the location of each nitrogenousbase in the DNA. He divided human DNA intoportions of different sizes and used the PCRtechnique to make thousands of copies. Hethen made in vitro copies of each DNAfragment using the cellular mechanism ofDNA replication. He added his own twist tothis process by using fluorescentdideoxynucleotides (ddNTP). These moleculescompete with standard nucleotides duringthe DNA replication process.

ELETROPHORESISOn a gel, the copiesof DNA traveldifferent distancesaccording to theirlength. Thismovement is calledelectrophoresis.

3

1 2 3 4 5

6 7 8 9 10 11 12

13 14 17 1815 16 19

20 21 22 X Y

Solution

GelElectrophoresis

Fragments ofDNA seen byfluorescence

ddGTP ddATP ddTTP ddCTP

UnknownSegment of DNA

NitrogenousBase

A T CG

Chromosomecontains tightly coiled and folded DNA. It consistsof sister chromatids that contain the same genes.

IN VITROSolutions with highconcentration of addNTP, for exampleddGTP, will producecopies of DNA ofdifferent length fromstandard nucleotides.It works because theDNA-copying process isinterrupted if a ddNTPis inserted instead of astandard nucleotide.

2

MULTIPLICATIONEach segment of DNA in whichthe sequence of bases isunknown is subjected to thepolymerase chain reaction(PCR), which makes it possibleto make thousands of copies ofthe same segment of DNA.

1

PUZZLEBy placing the gel in frontof UV light, the researchercan observe how the basesfit and form the exactsequence of bases of theunknown DNA segment.

4The lighter-weightcopies travel agreater distance inthe gel.

The first transgenictomato is made.

UMBILICAL CORDThere are manystem cells becausethey are notdifferentiated.

Cellular DivisionAll the cells of higherorganisms divide and multiply

through mitosis, with the exceptionof the reproductive gametes. Mitosisis the process through which a celldivides to form two identical cells.For this to happen, the first cellcopies its genetic material inside thenucleus, and later it slowlypartitions until it fully divides,producing two cells with the samegenetic material. An adult celldivides on average 20 timesbefore dying; a stem celldoes it indefinitely.

HEARTStem cells arebeing used torepair the heartafter an infarction.

BLOODReproduced invitro, the stemcells are theninjected.

RED BLOODCELLGeneratingthem in vitrohas beenachieved.

NEURONShave yet to begrown in thelaboratory.

ACTIVATORSChemical and hormonalactivators guide thespecialization.

WHITEBLOOD CELLSome testshave managedto producethem.

ObtainingBecause the stem cells are thefirst that form afterfertilization occurs, they areabundant in the placenta andespecially in the umbilical cord.Geneticists obtain them fromthe cord once the baby hasbeen born, and it is possible tofreeze the cord to harvest thestem cells later.

MITOSISThe cells multiplyaccording to theirgenetic program.

STEM CELLSdivide indefinitelywithout losingtheir properties.

STEMCELLS

STEMCELL

FIRST USEIn 1998 stem cells were isolatedand cultivated for the first time inthe United States. Since then,numerous laboratories in the worldhave cultivated them. Because ofethical questions that surroundwork with embryonic cells, eachline is monitored through officialorganizations.

EMBRYONIC CELLSThis photograph showsthe eye of a needle withan embryo formed only bystem cells before cellulardifferentiation begins.

NUCLEUScontains the DNA.First it duplicatesthe DNA, and thenit divides.

CYTOPLASM

DifferentiationThe stem cells are pluripotent, which is to saythat they have the power to create any of themore than 200 different cells of the body. Thisprocess happens as the embryo grows. If theoptimal conditions could be created in vitro, itwould be possible to form in a laboratory all

the cells of the body using the geneticprogram of the cells. In practice, this

technique is possible only witha few types of cells, in

particular blood cells.

199827 lines

2000

2003 2006 225 lines

200THERE AREMORE THAN

TYPES OF CELLSIN THE HUMAN

BODY

IS THE LIMIT FOR CULTIVATION. THISLIMITATION GUARANTEES THE ABSENCEOF A HUMAN EMBRYO. THE EXACTNUMBER IS DEBATED.

16 cells


Stem CellsT

he reasoning is simple: if an organism with more than 200different types of cells is formed from a group ofembryonic cells without specialization, then manipulating

the division of these original cells (called stem cells) shouldmake it possible to generate all the human tissues and evenproduce autotransplants with minimal risk. Although such workis in progress, the results are far from being a medical reality.Scientists all over the world are studying its application.

1

MultiplicationOnce isolated, stem cells are cultivatedin vitro under special conditions. It iscommon to resort to a substrate ofirradiated cells, which serve as supportwithout competing for space. Later,every seven days, they need to beseparated to keep them from dying andto be able to reproduce them.

2

ImplantationDoctors and geneticists hope to be able toprovide new pluripotent cells to damaged tissueand provoke its regeneration. To date, they havebeen able to introduce umbilical-cordhematopoietic stem cells into patients withdysfunctional formation of red blood cells. Thisis equivalent to a bone marrow transplantwithout surgical intervention.

4

3

The term “cloning” itself provokes controversy. Strictly speaking,to clone is to obtain an identical organism from another throughtechnology. The most commonly used technique is called somatic-cell nuclear

transfer. It was used to create Dolly the sheep as well as other cloned animals, including these Jerseycows. The technique consists of replacing the nucleus of an ovule with the nucleus of a cell from adonor specimen. When the ovule then undergoes division, it gives rise to an organism identical to thedonor. With all such processes, there exist slight differences between the donor and the clone. In onlyone case is the clone perfect, and it comes naturally: monozygous (identical) twins.

NUCLEUS OF THE CELL TO CLONEThe nucleus istransferred to the ovule.

Cow Cloning

78 THE AGE OF GENETICS

Obtaining theNucleusA specialized cell of an adult animal, whoseDNA is complete, is isolated, and it iscultivated in vitro to multiply it. Various ovulesof a donor cow are also isolated. The nucleus isthen removed from both groups of cells—onlythose of adult cells.

1

InseminationThe blastocyst is implanted in the uterus ofa donor cow on the sixth day after the cowhas stopped being in heat so that thedevelopment of the blastocyst continues ina natural way. If everything goes asplanned, the blastocyst adheres to theuterine wall.

5

FusionBy means of light electricdischarges, fusion of thedonated nucleus with thecytoplasm of the ovule isinitiated. Three hours later,calcium is added to the cell tosimulate fertilization. Aninterchange begins between thenucleus and the cytoplasm, andthe cell starts to divide.

3

Nucleus TransferConsists of replacing the nucleus of the ovulewith that obtained from the adult cell. In thisform, the chromosomes carried by the newnucleus complete the ovule in the same way asif the ovule had been fertilized by aspermatozoon. Once fused, the cell will beginits program of division as if it were a zygote(fertilized ovule).

2

Development of theFetusOnce the blastocyst is implanted, its growth begins. Thenormal period of gestation for a cow is from 280 to 290days. Because all the genetic information required wasprovided by a donor-cell nucleus, the calf that is born is anexact copy of the donor animal. It differs only in themitochondrial DNA, which was provided by the receptor ovule.

6

PIPETTEIt is used tointroduce thenucleus intothe ovule.

OVARY

OVIDUCT

INFUNDIBULUM

VAGINA PIPETTE

UTERUS

BLADDER

CERVIX

RECTUM

PIPETTEsupports the ovuleand prevents itfrom shifting in theoperation.

OVULE WITHOUTNUCLEUSOnly the cytoplasm,with organelles likemitochondria,remains.

NUCLEUSEXTRACTIONA fibroblast isextracted from the earof an exemplary adult.

Nucleus withComplete DNA

(60 chromosomes)

Ovule WithoutNucleus

OVULE EXTRACTIONAn ovule is obtainedfrom the ovary ofanother exemplaryspecimen, and thenucleus is removed.

2 cells

8 cells

The technology is still not efficient. Forthis Jersey, 934 ovules were

transferred, of which 166 fused, andonly one developed successfully.

Cost

CultivationThe new cell is cultivated in vitro,where it multiplies until forming ablastocyst (cellular group whosecells are not yet differentiated byfunction and is a precursor to anembryo). The developing blastocystis maintained in a medium thatcontains hormones and 5 percentoxygen to simulate the conditions ofa cow's uterus. After a week, thedeveloping mass has become largeenough that it can be implanted intothe actual uterus of a cow.

4

BLASTOCYST

Cloning can be applied for obtainingnew organisms and tissues and forreproducing segments of DNA.

DIVERSE USES

16 cells


Biochip Applications

GLASSSUBSTRATEis chemically treated withcertain reactive groups topermit the implantation ofthe oligonucleotides.

MASKTemplate withmicroarray of cells

PHOTODEGRADABLEFILM functions as anintermediary layer.


ProcedureThis biochip has a template, or pattern—called a geneticmicroarray—that makes it possible to compare the DNAof one tissue sample from a person with the genes thatcause a disease. In the case of a particular type ofcancer, for example, researchers want to know the genesthat are involved in the disease.

How It WorksOnce the injection of the markingmix is finished, it is necessary todetect which stuck to what spot. Forthis, the array is placed in a scannerwith a green and a red laser, whichexcite the fluorescent targets. Themicroscope and the camera work inconjunction to create an image, andthis information is stored in acomputer.

SMALL SIZE Biochips are the size of a stampand are contained in a glassstructure.

RED The gene foundin this spotexpressescancerousconditions.

ResultsAll the points of the marked biochip have smallsequences of DNA that are compared with asequence of the samples. The fluorescent signals,detected by means of a computer, indicate whichof the DNA sequences on the chip havecomplementary sequences in the sample. A specialprogram is used to calculate the proportion of redto green fluorescent signals in the image.

GREEN The gene found in thisspot expressesnormalconditions.

MIXThe tubes of green and redmarkings are combined inthe same tube.

0.3 inch(6.4 mm)

0.2 inch(4.5 mm)

Cells ofCancerousTissue

Cells ofNormalTissue

CANCERThe cDNA of cancerouscells is colored with a redfluorescent marking.

COMPUTERThe pattern is input into aspecial computer where themicroinjectors will take careof filling the 96 orifices, orspots, on the biochip.

NORMALThe cDNA(complimentaryDNA) of normalcells is coloredwith a greenfluorescentmarking.

1

2

4

5

Devices that use a small, flat substrate (chip) that contains biological (bio)material are commonly called biochips. Biochips are used for obtaininggenetic information. A biochip is a type of miniaturized equipment that

integrates tens of thousands of probes made up of genetic material having aknown sequence. When the probes are placed in contact with a biological sample(such as from a patient or experiment), only the nucleotide chains complementaryto those of the chip hybridize. This action produces a characteristic pattern light,which is read with a scanner and interpreted by a computer.

SamplesA microinjector fillseach one of the pores inthe biochip withsamples of the differentsequences of genesfrom the organism.

Spots filled withcDNA marked withboth fluorescentsubstances

3 MicroinjectionThrough microinjection, each spotis filled with cDNA marker of bothfluorescent substances (comingfrom cancerous and normaltissues combined).

YELLOWThe gene found in thisspot expressesnormalconditionstogether withthose ofcancer.

LIGHTRAYS

COLORFILTER

ADENOVIRUSIts genetic makeupis modified so itcan carry thesequence that willbe introduced.

PROTEINThe absence of a proteinthat results from agenetic error and thefailure to synthesize theprotein can have seriousconsequences.

DNA holds thesequence thatrepairs thetargeted gene.

MODIFIEDDNA

MODIFIEDDNA

NEWHEALTHYCELL

NEWHEALTHYCELL

AFFECTEDCELL

MODIFIEDDNA

NUCLEARPORE

CELLNUCLEUS

Illnesses with a genetic origin aredifficult to treat, since the organism has

poorly coded genes and the fault is thereforepresent in all its cells. Cystic fibrosis andDuchenne muscular dystrophy are examples ofmonogenetic illnesses that can potentially be

treated with these therapies. Gene therapy hasalso been attempted on cancer and HIVinfection, among other pathologies. Adefinitive cure may be found for many geneticillnesses, but the techniques for gene therapyare still in the development stage.

Treatable Illnesses

Damaged geneto be modified1

1 2 3

Addedhealthy gene2

DNATRANSCRIPTION

HERPESVIRUSThe herpesvirus is an icosahedral virusand holds a DNA sequence that needs tobe modified so that it will not cause anillness. It is widely used in gene therapy.

NONVIRAL GENE THERAPIESMany are based on physical means such as electricaltechniques. They have the advantage of producingmaterial in vitro, which allows for a large transfercapacity not limited by the number of bases that can betransfected by a virus. The problem is that thesemethods are not efficient for reaching target cells in theorganism. The most important therapies of this type aremicroinjection, calcium phosphate precipitation, andelectroporation (the use of an electric field to increasethe permeability of the cell membrane).

The unit in which DNA and RNA aremeasured; the capacity of a virus's

cassette, which on average isapproximately five kilobases.

Kilobase

It is critical that the hypothetical number of cells tobe modified and the number of viruses needed forthe therapy to work are in the correct relationship.

Relationship

SynthesisThe infected culture cells, which have the newgenetic information, can now synthesize thecompound that caused the dysfunction.Generally these are proteins that cannot besynthesized because the gene for theirelaboration is disassociated or damaged. Theprocess begins once the cells divide andtranscribe the gene in question. The proteinthat was not synthesized before is nowtranscribed and produced.


Gene TherapyO

ne of the latest breakthroughs in medicine, gene therapy is usedto introduce genetic material to correct deficiencies of one ormore defective genes that are the cause of an illness. Several

different techniques have been developed for use with human patients,almost all of which are at the research stage. The problem withillnesses with a genetic origin is that therapy must modify the cells ofthe affected organ. To reach all these cells, or a significant number ofthem, demands elaborate protocols or, as is the case for viruses, theuse of nature's biological weapons to cause other illnesses.

IdentificationThe DNA sequence that corresponds tothe gene that causes the deficiencyrequiring treatment is identified. Thenthe correct sequence is isolated andmultiplied to guarantee a quantity thatcan modify the organism. Because amonogenetic illness generally affectsthe function of one organ, the cellvolume that is targeted formodification is large. Then a techniqueis chosen to transfect the cells.

1

VehicleAn adenovirus is an icosahedral virusthat contains double-stranded DNAand lacks an outer envelope. It isprimarily the cause of a number ofmild respiratory illnesses. If the viruscan be modified to be nonpathogenic,it has the potential for use intransporting a modified sequence ofDNA in a region called a cassette.Even though its capacity is limited, itseffectiveness rate is very high.

2

ReplacementThe modified adenovirus isinoculated in a cell culture togenerate the viral infection. It thenenters the cells and multiplies inthe cytoplasm, copying its DNA,including the modification carriedin the cassette, in the nucleus ofthe infected cell, where ittranscribes the new information.

3

4

is the minimum number of coinciding pointsthat need to be found for a suspect to beaccused of a crime in the United States.

13 locations


DNA Magnification3

Since Sir Alec Jeffreys developed the concept of the DNA profile forthe identification of people, this type of forensic technique has takenon significant importance. A practically unmistakable genetic footprint

can be established that allows for the correlation of evidence found at the sceneof a crime (hair, semen, blood samples) with a suspect. In addition, the use of thistechnique is a key element to determine the genetic link in kin relationships.


Sample Collection

Each sample is placedin separate plasticbags, sealed, andcertified to avoidadulterations.

MICROPIPETTEOnly the substancefloating on the surfaceis extracted. This iswhere the DNA is.

HAIR FOLLICLEA follicle has DNA thatis easy to obtain.

1

TWEEZERSmust be properly

sterilized.

DISPOSABLEMATERIALAll the materialthat is used mustbe disposable toavoid contaminatingthe DNA.

Power of Exclusion (PE) Overall, for a DNA test to be considered asvalid criminal evidence, at least in theory, it

should be able to guarantee a PE with a certaintyabove 99.9999999 percent. The PE is measured asa percentage but is expressed as the number ofpeople who are excluded as possible bearers of theDNA at the crime scene. Thus, a sample is taken atrandom from one person, as a type of witness, andit is then compared with the DNA from theevidence and that of the suspect. The detail of theanalysis must be so precise that it can, at leasttheoretically, be able to discriminate one personamong one billion people. In practice, the test isvalid if it statistically discriminates one person inone billion. All this is done to guarantee the resultsof the test and so that it can have validity in court.In practice, the suspects are not chosen randomlybut fulfill other evidence patterns, among whichDNA is used to confirm these patterns.

DNA Footprints SWABFor saliva samples.

Then it is immersedin a solvent

solution andthe DNA

extracted.

is the STATISTICAL GUARANTEE.

1:1 billion

1:100 million

GUARANTEED POWER OF EXCLUSION

Impression andComparison

4The machine presents the results as curves,where each base has a specific locationaccording to the height of the curve in the graphsequence. It then compares the sample obtainedat the crime scene with those obtained from thecrime suspects. If one of them was at the sceneof the crime, the curves coincide exactly in atleast 13 known positions.

Any body fluid, such as urine, blood, semen, sweat, andsaliva, or fragments, such as tissues, cells, or hairs,can be analyzed to obtain a person's DNA. There isgenerally always something left at the scenethat can be used as a sample.

LABELINGis absolutely necessaryso that the samples arenot mixed up.

HAIR DIGESTIONThe hair is divided into

sections. These are then putinto a tube, and solventsare applied.

1

SURFACE-FLOATINGSUBSTANCE

A 70 percent solution of ethanolis added, and the mixture is rinsedwith water. The DNA is free ofimpurities and ready for analysis.

4

DNA-EVIDENCEGRAPH

CENTRIFUGINGThe suspended DNA

must be centrifuged toseparate it from the restof the cell material.

2

DNASeparation

2

Heat is one of themost destructivefactors.

FACTORS THAT ALTER DNA

Moisture or waterwill denaturalize asample faster.

Only a very smallamount ofevidence isneeded forsampling. Forexample, just a smallfraction of a drop of bloodor sperm is sufficient.

COINCIDENCEOF GENETICPATTERNS

ADENINE

CYTOSINE

THIAMINE

GUANINE

Forensic DNA

Filial DNA

DNA GRAPH FORSUSPECT A

DNA GRAPH FORSUSPECT B

The numbers representa position in the DNAsequence.

is the WORLD'S POPULATION.

The polymerase chain reaction (PCR) is carried out by amachine that, using heat, synthetic short nucleotidesequences, and enzymes, copies each fragment of DNA asmany times as needed. This amplification makes itpossible to conduct a large number of tests while

conserving the DNA. Later the DNAfragments are separated by means ofcapillary electrophoresis.

6,500,000,000

1 in 1,000,000,000

Visualization ofthe DNA as curveson the monitor

PRECIPITATIONA 95 percent solution of ethanol is added; thesample is shaken andthen centrifuged at ahigher speed than before.

3

Surface-floating

substanceand pellet

DNA and pelletof leftovermaterials

Genetically modified foods have always existed. An example is wine,modified through the fermentation of grapes. However, modernbiotechnology based on DNA decoding has made these

processes predictable and controllable. The process improvesspecific characteristics of the plant, makes it more resistantto pests, and improves its nutritional quality. Theobjective is a greater production of food with betteragronomic and nutritional characteristics.

Modified Foods


Cloning theDesired GeneAll the DNA is extracted from theBacillus thuringiensis bacteria inorder to locate and copy the generesponsible for this characteristic.

1

Modified GeneDesignThe gene is composed of a codifiedsequence (wanted gene) and ofregulatory sequences, which can bealtered for the gene to be expressedin a desired form. The selected geneconfers an advantage, for instance,resistance to an herbicide.

2

TransformationThe modified gene is inserted into thenucleus of the corn cell so that it canbe incorporated into some of thechromosomes. For this effect, the genepistol, or gene cannon, is used.

3

TRANSGENICBACTERIARecombinant plasmids enter the bacteria that willexpress the genes.

DESIRED GENEBacteria multiply toobtain a copy of each oneof the thousands of genesfrom the organism. Thedesired gene is locatedand hundreds of copiesare made.

Petri Dish

GoldParticle

Hundreds of goldparticles are coveredor plated withthousands of copies of the new gene.

The gold particlesare shot towardthe cell sample.

If the particle enters the nucleus, thegenes are dissolved and can be incorporated into the chromosomes' DNA.

BT Cornhas been genetically modified to make it resistantto the western corn rootworm, a pest that feedson the root of the plant. Bt corn produces the Bttoxin, a toxin naturally produced by a soilbacterium. The pest is killed either when thelarvae attempt to feed on the root or the adultsattempt to feed on the foliage of the Bt corn.

The marine strawberryResearch has been conducted in modifying strawberrieswith a gene from the plaice to make the fruit moreresistant to frost. This is a simple process from whichthe crop yields can be improved by a high percentage.

Golden riceGolden rice is the first organism that wasmodified genetically for the purpose ofproviding an increased level of vitamin A forpopulations with a deficiency in the vitamin.The embryo of golden rice stores betacarotene and other carotenes,which are the precursors ofvitamin A.

More benefitsThe development of transgenic plants has allowed theproduction of food with more vitamins, minerals, and proteins,

or with less fat. The development of genetic technology has also beenable to delay the maturation of fruits and vegetables and, in othercases, make them more resistant to specific pests, thus reducing theneed for applying insecticides to crops. The genetic modification ofsome crops also produces smaller and stronger plants, whilesimultaneously increasing their yield, because they invest moreenergy into producing their edible parts.

DNA

DesiredGene

bacterium Bacillusthuringiensis

The genes used are those thatencode for the enzymesphytoene synthase and lycopenesynthase in the plant Narcissuspseudonarcissus and the enzymecarotene desaturase fromErwinia uredovona bacteria.

1

The new transgenic strawberry canreproduce as many times as it wants.4

The DNA strands fromthese genes are insertedinto plasmids, which arelater introduced intoAgrobacteriumtumefaciens bacteria.

2

Agrobacteria areinoculated into immaturerice crop embryos.

3

RESTRICTION ENZYMEThe enzyme is added to the cloned DNA in atest tube to segment or divide it into piecesthe size of the gene. The bacterial plasmidsthat were extracted using the same enzymeare added in another test tube.

Transgenic plants areobtained from thesecrop embryos, whichgenerate transgenicrice grains with extravitamin A in itsendosperm.

4

CultureThe transgenic corn cells are distributedin crop media that contain the necessarynutrients. Those that proliferate form awhole plant from transformed cells. Theadult transgenic plants are transplantedto the agricultural fields. This transgeniccorn and its descendants will beresistant to the western corn rootworm.

4

CONJUGATIVEPLASMIDSThe plasmids are mixedwith DNA bits to formconjugative plasmids.

P WANTED GENE

ELECTRICALPULSESBacteria are added,and quick electricalpulses are applied thatcause the plasmidswith the transgene toenter the bacteria.

Corn CellCulture

Nucleus

Chromosome

The gene that keeps theplaice from freezing iscopied and spliced into aplasmid taken from abacterium.

1

The plasmid from thebacterium that holdsthe plaice gene isthen inserted onto asecond bacterium.

2

A strawberry cell cultureis infected with theantifreezing gene. This is then integrated intothe strawberry DNA, and plant transgenesistakes place.

3

BacteriaDNA

Antifreezinggene

Strawberrycell

Antifreezinggene

Secondbacterium

Endospermwherevitamin Aaccumulates

Agrobacteria

Plasmids

Narcissuspseudonarcissus

Plasmid with InsectToxin Transgene

Recombinantplasmids

Bacteria

Test tube

The labelsTransgenic foods have their own label. This is alegal requirement in most countries. When the

time comes to shop for fruits, vegetables, or cereals atthe supermarket, we must look closely at the labels. In the case of corn or rice, only 9percent should be transgenic.This should be clearlyexplained in the list ofingredients.

Endogenous Bacterial Plasmid

Erwiniauredovona

T P SELECTED GENE T

Pharmaceutical Farms


Atransgenic animal is one in which foreign genes havebeen introduced through genetic engineering,integrated into the animal's genome, and transmitted

from generation to generation. The first achievements inthis field were made with cell cultures, and the first “whole”animal that was obtained with an exogenous gene was arat. Other mammals, such as rabbits, pigs, cows, sheep,goats, and monkeys, are being genetically manipulated formedical or animal-production purposes.

Hypoallergenic CatsCat lovers who have not been able to fulfill theirdreams of having a cat as a pet because of theirallergies are giving a hint of a hopeful smile. A U.S.company had planned to genetically engineer cats toproduce a very low level of a saliva protein thatcauses allergic reactions in humans but later choseto use selective breeding.

Fluorescent ratsThe Research Institute for Microbial Diseases atOsaka University, Japan, obtained the FGP(fluorescent green protein) gene of the jellyfishAequorea victoria. The gene was introduced in thefertilized ovules of the female rat, which gestatesan animal that will have fluorescent skin under UVlight. One application was to mark cancer cells andsee how they travel around the body.

TRANSGENIC PIGSInvestigators at thePharmaceutical EngineeringInstitute of Virginia Tech holdthree of the specimens.

FACTOR VIIIis identified and the gene copied. Aprocedure is then worked out to causethis gene to be expressed only in themammary gland of the pigs so that thefactor is produced in their milk.

ANIMAL TRANSGENESISis accomplished with themicroinjection of thehuman gene of factor VIIIdirectly into fertilizedovules, so that thesequence integrates intoits genome.

Spiders with threads of steelRecombinant spider silk, called BioSteel, has been produced fromthe milk of goats implanted with the gene of the spider Nephilaclavipes, commonly known as the golden thread spider. Similar tonatural spider silk, the product was reported to be five timesstronger but lighter than steel, silky in texture, and biodegradable.

Gene forfactor VIII

Human genefor factor VIII

Pigs to cure hemophiliaScientists at the Pharmaceutical Engineering Institute ofVirginia Tech and colleagues added the gene for the factor VIIIprotein of human coagulation to a few transgenic pigs. Thisprotein is of vital therapeutic importance as a coagulant agentfor type A hemophiliacs.

1

2

IMPLANTThe ovule is implanted inthe uterus of an adoptivemother, which has beenhormonally prepared.

3BIRTHOnce the female transgenicpigs are born, it is necessary toverify that they have at leastone copy of the transgene.

4FACTOR VIIIis extracted from the milk.The protein is purified andthe desired pharmacologicalproduct obtained.

6MILK WITH FACTOR VIIIWhen adulthood is reached, thefemale pig produces milk withfactor VIII, which can helpthose sick with hemophilia.

5

Low CostThe proteins of factor VIII and factor IX

that are injected into patients withhemophilia come from human blood plasma

and are very costly. In contrast, in thefuture, an injection of such proteins purifiedfrom the milk of transgenic livestock could

cost only a dollar per injection.


Ever since Darwin published his theory about the evolution of species, humans have sought to understand their origin in light of a diversity of ideas and theories. With the success ofefforts to map the human genome, old evidence is gaining new strength. Many scientific teams

used some 100,000 samples of DNA from all over the world to trace the process of human expansionback to a common ancestor—the “Mitochondrial Eve” that lived in sub-Saharan Africa some 150,000years ago. She was not the only human female of her time, but she was the one that all present-daywomen recognize as a common genetic ancestor. The key to the trail is in DNA mutations.

The Genetic Ancestor

Mitochondrial DNAMitochondria contain circular DNA. This DNA hasonly one recombinable part, called HVR 1 and 2,where mutations can happen. Over time, themutations leave marks that can be traced accordingto their location from the ends to the center.Because mitochondria are inherited from the mother,the mutations can be traced back to a femalegenetic ancestor. This “Mitochondrial Eve” lived insub-Saharan Africa about 150,000 years ago. Shewas not alone at the time, nor was she the only oneof her species. However, she was the only one of hercommunity whose genetic inheritance survives.

Geneticists have determined statistically that everythree generations there is a mutation that will bepreserved in the DNA of the descendants. They usedthis statistic and demographic studies to calculatethe age of the “Mitochondrial Eve” and the “NuclearAdam.” If the path of mutations is followed fromthe present to the past, the line of ascent would

lead to these genetic ancestors. However, in reverse,many mutations represent dead ends. That is, theyleft no descendants for a wide range of reasons.These links are part of the study calledphylogenetics and make up well-definedhaplogroups. Each haplogroup represents thegenetic diversity of a species.

Genetic Diversity and Phylogenetics

is a human group with the same geneticdescent, recognized by characteristic

mutations.

Haplogroup

OvuleThis cell is a haploid cell that at the moment of fertilization providesthe cellular organellesas well as half of thechromosomes. Amongthe organelles, themitochondria are themost important forgenetic studies.

L0 and L1, the most ancientThese haplogroups have thegreatest number of mutationsin their DNA and are theoldest human groups. Theyare the San and Khoekhoepeoples in Africa.

Paternal Line

Great-grandparents

Grandparents

Children

Maternal Line

150,000years agoHomo sapiensis found onlyin Africa.

50,000-70,000years agoThey migrate toother continentsvia the Red Sea.

30,000-40,000years agoThey spread to therest of the world.

ParentsThird GenerationAccording toscientificcalculations, thisis when geneticmutations mayoccur.

First Generation

Second Generation

Fourth Generation

The common relativeIn genetic terms, DNA enables us to conceive of aprimordial Adam and Eve, our genetic ancestors. However,the common ancestor of all humans alive today is quite adifferent matter. Several scientific hypotheses estimatethat an ancestor to whom we are all related lived between1,000 and 10,000 years ago.

Genetic materialEach time an organism is conceived, its geneticmaterial is a fusion of equal parts received from

its parents. Recovering this material throughout historyis impossible because of the large number ofcombinations, so scientists use mitochondrial DNAfrom the cells as well as DNA from the chromosomes.Thus, following a single path for each sex, the possiblecombinations are reduced to a set of hereditary linesthat are traceable over time. This method is possiblewhen a cell's DNA, along with the various locations ofthe genes and recombinant areas, is known.

Genetic driftEach time a mutation occurs, it continues as a mark onfuture generations. Genetic drift explains how this

mutation spreads and how the effectiveness of its spread isrelated to the number of individuals in a group, the time they livein a certain region, and the environment. If the group is small, itschances of success are increased because genetic drift is moreeffective in changing the genetic pattern. Also, the longer thegroup remains in one place, the more mutations it will have.

Africa is where the greatestnumber of mutations is found.This leads to the suppositionthat humans have lived there the longest.

Other chromosomes

Y chromosome

Mitochondrial DNA

The Y chromosomeA baby's sex is determined by the sperm cell thatsucceeds in fertilizing the ovule. Specifically the malegender is determined by the Y chromosome, which ispassed on from father to son. To follow a line ofascendant mutations in the recombinant part, themarkers of each mutation must be read from theends to the center to find a common male ancestor.He is called the chromosomal Adam, and he isestimated to have lived 90,000 years ago in Africa.

is a set of closely linked alleles ona chromosome.

HaplotypeRecombinantRegion

RecombinantRegion

NonrecombinantRegion

RecombinantRegion

SpermatozoonWhen a spermatozoon fertilizes anovule, its tail breaks off, along withall cellular material except itsnucleus, which contains half of thenecessary genetic information fora new individual.

Mitochondriaare the organelles thatprovide energy to the cellthrough respiration. Theycontain a portion of DNA.

92 GLOSSARY EVOLUTION AND GENETICS 93

Glossary

AcidType of chemical compound. DNA, vinegar, andlemon juice are weak acids.

AdaptationA particular characteristic of an organism'sstructure, physiology, or behavior that enables itto live in its environment.

AlleleOne of several alternatives of a gene. Forexample, the gene for eye color can have brownand blue alleles.

Amino AcidOne of the 20 chemical compounds that livingbeings use to form proteins.

AnthropologistScientist who studies human beings from theviewpoint of their social and biologicalrelationships.

ArchaeologistScientist who studies human history based onthe objects humans have left behind, such asbuildings, ceramics, and weapons.

Artificial FertilizationTechnique for fertilizing ovules. It is usuallydone in vitro, after which the fertilized ovule isimplanted.

Artificial SelectionAs opposed to natural selection, humanintervention in the process of speciation;breeding animals or plants to improve theirtraits is an example.

BacteriaOne-celled organisms that are prokaryotic (theylack a nucleus bound by a membrane). Somecause illnesses, others are harmless, and stillothers are beneficial.

BacteriophageVirus that only infects bacteria; used as a vectorin genetic engineering.

BioballisticsRecombinant genetic technique that consists ofshooting small metal projectiles covered withDNA into a cell to penetrate the nucleus andrecombine the genes in the desired manner.

BiologistScientist who studies living beings.

BioprospectingThe taking of tissue samples from living beingsto find genes that can be patented to obtaineconomic benefits.

CellSmallest independent unit that forms part of aliving being.

Cell NucleusThe central part of a cell, it contains thechromosomes and regulates the cell's activity.In some cells it is well differentiated. Other cells,such as some bacteria and red blood cells, haveno nucleus.

Cellular MembraneFlexible covering of all living cells that containsthe cytoplasm. It is semipermeable andregulates the interchange of water and gaseswith the outside.

ChimeraIn Greek mythology, a monster with the head ofa lion, the body of a goat, and the tail of aserpent. In genetics, the hypothetical creation ofone being from the parts of others.

Chromosomal CrossoverA step during meiosis that corresponds to the

protein essential for the body's properfunctioning.

DiploidCell with two complete sets of chromosomes. Itis represented by the symbol 2n.

DNADeoxyribonucleic acid; molecule in the shape ofa double helix with codified genetic information.

DNA FootprintThe identification of a person by DNA; used inforensics.

DNA SequencingObtaining the structure of bases that make upDNA. The long DNA chain is often divided intosmaller fractions for study.

Dominant GeneGene that, when present in a pair of alleles, isalways manifested.

Double HelixShape of two spirals in geometric space. TheDNA chain has this shape.

DyslexiaDisorder, sometimes genetically based, thatcauses difficulties with reading, writing, andspeech.

EmbryoProduct of an ovule fertilized by a sperm cell. Itcan develop into an adult organism.

Endoplasmic ReticulumGroup of narrow channels that transportvarious types of substances and molecules fromone point to another inside a cell.

EnzymeProtein that helps regulate the chemicalprocesses in a cell.

Escherichia coli

Abundant bacteria often used in geneticexperiments.

EugenicsScience that seeks to improve humankind byselecting and controlling human genes. Itsobjectives are highly controversial.

EvolutionGradual change in a species or organism; notnecessarily an improvement. It was theorizedby Darwin in his famous book On the Origin of Species.

ExtinctionThe disappearance of all specimens of one ormore species.

FertilizationFusion of a male gamete with a female gamete,forming a zygote, which can develop into a newindividual.

Filler DNALong, repeated sequences of DNA that do not provide genetic information. Also calledjunk DNA.

ForensicsScientific discipline of the study of evidence of a crime.

FossilAll traces of past life, even those that have notbeen petrified.

GameteReproductive cell, also called sex cell, such assperm and eggs.

GeneUnit of information of a chromosome; sequenceof nucleotides in a DNA molecule that carriesout a specific function.

GenerationA “level” in the history of a family or species.There is one generation between parents andchildren.

Gene TherapyTreatment of certain diseases of genetic originby replacing the patient's defective gene(s) withthe correct gene(s) to cure the disease.

Genetic DiseaseDisease caused partially or wholly by a geneticdisorder.

Genetic EngineeringThe study of the application of genetics inrelation to technological uses.

GeneticistScientist who studies genetics.

Genetic MutationError in the copying of a cell's DNA. A fewmutations can be beneficial and intensify thecell's original qualities. Mutations are believed tohave generated the evolution of species. Mostgive rise to closed evolutionary lines.

GeneticsThe study of DNA and genes.

Genetic TraitPhysical trait transmitted to an organism'sdescendants, such as hair color and height.

interchange of genes between diploidchromosomes and causes the recombination ofgenes.

ChromosomeSequence of DNA coiled inside the nucleus of acell. One cell usually has more than onechromosome, and together they make up thegenetic inheritance of an individual.

CloneA living being that is identical to another. It alsorefers to parts, such as organs or fragments ofDNA, that are identical.

CloningAction of producing a clone.

CoevolutionWhen more than one species evolve together,and the changes in one cause the others toundergo modifications in mutual adaptation.

CytoplasmWatery or gelatinous substance that containsorganelles and makes up most of the interior ofthe cell, except for the nucleus.

CytosineOne of the four bases that make up the DNAmolecule.

DescendantFamily member belonging to later generations,such as a child, grandchild, or great-grandchild.

Designer BabyHuman baby selected as an embryo based on aset of genetic traits chosen before its birth.

DiabetesDisease that prevents the body fromsynthesizing the necessary amount of insulin, a

94 GLOSSARY EVOLUTION AND GENETICS 95

GenomeComplete set of genes of a species.

HaploidFrom the Greek term haplous, “one”; a cell withonly one set of chromosomes, unlike diploidcells. Gametes are haploid cells.

HelixGeometric spiral shape equivalent to a curvealong a cylindrical surface; the shape in whichthe DNA molecule is curled.

HemophiliaA group of hereditary diseases caused by thelack of a clotting factor (the most importantbeing Factors VIII and IX). Its most commonsymptom is spontaneous hemorrhaging.

HeredityIn genetics, all types of genetic material passedon by the parents to a descendant.

HormoneGlandular secretion with the function ofstimulating, inhibiting, or regulating the actionof other glands, systems, or organs of the body.

KaryotypeOrdering of the chromosomes of a cellaccording to shape, number, or size.

KeratinProtein found in skin, hair, and nails.

LigaseProtein used by geneticists to join sections of DNA.

LysosomePart of the cell that breaks down and reusesworn-out proteins.

MeiosisType of double cell division that forms fourdaughter cells out of one cell, each one withone-half the chromosomes of the original cell;typical in the formation of gametes.

MitochondriaCellular organelle that combines food andoxygen to produce energy for the cell.

Mitochondrial DNASmall amount of DNA contained in themitochondria of the cell.

MitosisCellular division that produces two geneticallyidentical daughter cells. The most common formof cell division.

MoleculeMinimum quantity into which a substance canbe divided without losing its chemicalproperties. The level immediately below it is theatom.

Monozygotic TwinsTwins who develop from a single zygote thatsplits in two, forming two genetically identicalindividuals.

MummyHuman corpse preserved by artificial methods,which can be preserved for long periods of time.The genetic study of mummies provides muchevidence about life in the past.

Natural SelectionProcess in which only the organisms that arebest adapted thrive and evolve. This selection iscarried out without human intervention.

Nitrogenous BaseType of chemical compound. Four distinct typesof bases in DNA make up the genetic code,according to their combinations.

Recessive GeneGene that, even though present, might or mightnot be manifested in a pair of alleles dependingon the presence of a dominant gene.

Recombinant DNASequence that contains a combinationoriginating from one or more organisms.

ReplicaExact or nearly exact copy of an original. A viruscreates replicas of itself after invading a cell.

RepressorProtein that binds to a DNA chain in order tostop the functioning of a gene.

ReproductionSexual or nonsexual creation of other organismsof the same species. The fertilization of gametesis sexual, whereas parthenogenesis is not.

Restriction EnzymeProtein in certain bacteria that can cut the DNAmolecule.

RibosomePart of a cell that reads the instructions of thegenes and synthesizes the correspondingproteins.

RNARibonucleic acid, similar to DNA but used totransport a copy of DNA code to the ribosome,where proteins are manufactured.

RNA PolymeraseEnzyme that serves as a catalyst for synthe-sizing an RNA molecule based on DNA code.

Selective BreedingThe production of plants or animals that displaythe results of artificial selection of their genetictraits. Agronomists, veterinarians, and

geneticists use selective breeding to improvecertain species and breeds or varieties toachieve, for example, greater productivity andcrop yields.

Sex CellsSpecial cells, also called gametes, with areproductive function. Some examples areovules, spermatozoa, and pollen.

SpeciationEvolutionary process in which a new species is formed, for various reasons, from anotherspecies.

SpeciesThe lowest unit of classification in evolution. Itwas originally defined according to thephenotype of each individual. The field ofgenetics has raised new questions about whatconstitutes a species.

Spermatozoon (Sperm)Male gamete or sex cell.

Stem CellCell with the ability to develop into a specifictype of cell or bodily tissue. Pluripotent stemcells can develop into any type of cell of the body.

TelomeraseProtein for repairing the telomere of achromosome. Found only in certain cells.

TelomereDNA sequence at the end of a chromosome, it isshortened every time the cell divides. Thenumber of times the cell can divide depends onthe length of the telomere.

ThymineOne of the four bases that make up DNA,combining in different sequences to form genes.

TranscriptionProcess of copying a strand of DNA onto acomplementary sequence of RNA with theenzyme RNA polymerase.

TransgenicDescribes plants or animals of one species thathave undergone genetic modifications using oneor more genes from another species.

VectorIn genetic engineering, the agent thatintroduces a new sequence of DNA into anorganism. Viruses and bacteria are often usedas vectors.

VirusOrganism composed of DNA or RNA enclosed ina capsid, or protein structure. A virus can invadecells and use them to create more viruses.

X ChromosomeOne of the chromosomes that determines aperson's sex.

Y ChromosomeChromosome that determines the male sex;passed on only from fathers to sons.

ZygoteThe first cell of a sexually reproduced organismformed from the union of gametes.

OrganelleAny organ of a cell, including mitochondria,ribosomes, and lysosomes. They carry outspecific functions.

OvuleFemale gamete, or sex cell.

PancreasOrgan that produces insulin, located below thestomach.

PCR (Polymerase Chain Reaction)Technique for multiplying fragments of DNAusing polymerase.

PhenotypeIn biology, the visible manifestation of agenotype in a certain environment.

PhylogeneticsThe study of evolutionary relationships betweenthe various species, reconstructing the history oftheir speciation.

Preimplantation Genetic DiagnosisMethod of in vitro selection of embryos basedon preferred genetic conditions. They are thenimplanted in the uterus for normal development.

ProteinNatural or synthetic compound of amino acids,which carries out important functions in anorganism.

RadioactivityEnergy given off by certain chemical elements; itcan cause genetic alterations or even diseasessuch as cancer.

96 INDEX EVOLUTION AND GENETICS 97

Index

AAcanthostega, 20, 29Adam and Eve, 9, 90, 91adaptation, 14, 16, 28, 42adenine, 60, 61, 85adenovirus, gene therapy, 82Africa

first hominids, 42-43genetic mutations, 91human evolution, 4, 48-49human migration, 45Pliocene epoch, 38-39religion, 8

African buffalo, 14agriculture, 53agrobacteria, 87Albertosaurus, 10allele, 66, 67allergy, hypoallergenic cats, 89Allosaurus, 31amniote, 36, 37amniotic egg, 29, 36amphibian, 20, 28-29, 36anaphase, 64, 65angiosperm (plant), 36 animal

beginnings, 23characteristics, 36-37classification, 37early forms, 21genetic modification, 88-89mass extinctions, 31number of species, 37See also types of animals, for example, fish;

mammal; reptileAnomalocaris, 26-27antibiotic, 70-71aquatic life

anaerobic respiration, 20Cambrian explosion, 26-27earliest, 24-25, 26-27See also fish

arachnid, tree of life, 37

archaea (microscopic organism), 36archaeology, 42-43, 45, 52art, 50-51, 52arthropod, 27

arachnid, 37crustacean, 37hermit crab, 14insect, 37moth, 12spider, 89tree of life, 37

asteroid, mass extinction theories, 32-33atmosphere, 20, 21, 22Australopithecus, 4, 40, 42-43Australopithecus afarensis, 21, 42, 43autosome, 74

Bbacteria, 37

aerobic, 23beginnings, 21, 22chromosome, 59genetic modification, 66, 70, 86, 87

Barosaurus, 21Baryonyx, 31Bible, 9binocular vision, 34biochip, 80-81BioSteel, 89bipedalism, 31, 40, 42bird

cattle egret, 14first appearance, 21, 31honeycreeper, 16tree of life, 37

blastocyst, 79bone, 29, 30, 41bony fish, tree of life, 37bottleneck effect, genetics, 13Brahma, 8brain

Cro-Magnon, 48

cladogenesis, 16cladogram, 36-37, 40-41climate, 52cloning, 78-79, 86cnidarian, 18, 25, 36coevolution, 14-15commensalism, 14competition, 15complimentary DNA (cDNA), 80, 81continent, present-day, 38continental drift, 20-21coral reef, 27corn, 86-87cow, cloning, 78-79crab, 14creation, 8Cretaceous Period, 21, 30, 31, 32Crick, Francis, 60, 66criminal investigation, 84-85crinoid fossil, 20Cro-Magnon, 5, 48-49crop, 86-87cross-pollination, 67crustacean, 37cult, 53culture, human, 50-51, 52-53cyclomedusa, 25cystic fibrosis, 82cytokinesis, 56, 65cytoplasm, 23, 65, 76cytosine, 60, 61, 85

DDarwin, Charles, 12Devonian Period, 28Dickinsonia, 25dinosaur, 30-31, 32-33

era of reptiles, 21fossils, 10-11heaviest, 21

disease, genetic, 74-75, 82-83DNA (deoxyribonucleic acid), 60-61

analysis: See DNA analysisappearance, 59biochips, 80cellular division, 54-55, 56-57chromosomes, 58-59 cloning, 78-79codons, 63complimentary DNA, 80, 81defined, 54discovery, 60, 66double helix, 60-61, 66duplication, 56early eukaryotes, 22engineered: See genetic engineeringextraction, 70, 84-85genes, 58gene therapy, 82-83genetic mutation, 13markers, 72-73meiosis, 54-55mitochondrial DNA, 11, 74, 79, 91mitosis, 54-55Neanderthals, 48nucleoplasm, 23nucleotides, 59, 61polymorphism, 73polypeptides, 63prokaryotes, 58-59recombinant DNA, 70-71replication, 60separation, 62-63tracing, 90transcription, 62-63, 82-83

DNA analysisbiochips, 80-81forensics, 84-85human genome, 74-75markers, 72-73microsatellites, 72-73mitochondria, 90uses, 68-69

dog, 17Dolly (sheep), cloning, 66, 78dolmen, 52dominant allele, genetics, 66

dorsal spine, 29, 42double helix: See DNADunkleosteus, 28

EEarth, 20-21, 22-23, 34Eden, 9Ediacaran fossil, 20, 24, 25eel, 27egg, 29, 36egret, 14Egypt, 9electrophoresis, 73, 75embryonic cell, 76endoplasmic reticulum, 23enzyme, 60eukaryote, 22, 23, 36, 58evolution

adaptation, 14, 16, 28, 42beginnings, 36bone, 29brain, 4, 41, 44Cambrian explosion, 26-27evidence, 10-11fins to limbs, 29genetic mutations, 10, 13, 16human: See human evolutionmolecular, 23multiregional, 49natural selection, 10, 12, 15origin of species, 16-17Paleozoic Era, 28-29phylogenetic tree, 36-37, 40-41processes, 12-13relationships between species, 14-15See also specific types of organisms, for

example, plant; primateextinction

dinosaurs, 31, 32-33mass extinction, 20-21, 32-33Neanderthals, 47

eye, genetics of eye color, 66

evolution, 4, 44human evolution, 40, 41Neanderthal, 46, 47

buffalo, 14Burgess Shale fossil bed, 26-27

CCambrian explosion, 18-19, 20, 24, 26-27Cambrian Period, 24, 25, 26-27Carboniferous Period, 29cartilaginous fish, 36cat, 10, 89Çatal Hüyük (Turkey), 52-53cattle egret, 14cave painting, 50-51cell

chromosome, 56, 57, 58-59, 64-65division: See cellular divisioneukaryotes, 22, 23, 36, 58nucleus, 23, 56, 65prokaryotes, 58-59replication, 60-61stem, 76-77transcription, 62-63types, 77

cellular division, 54-55, 56-57, 58-59, 64-65, 76, 83

Cenozoic Era, 21, 34centrifugation, 71centriole, 23centromere, 57, 58Charnia (fossil), 24Chicxulub (Mexico), meteorite, 33chimpanzee, 40, 41, 42chloroplast, 23chordate, 27Christianity, 9chromatid, 57, 58chromatin, 58chromosome, 56, 57, 58-59, 64-65, 74, 75city, 52-53cladistics (classification technique), 37

98 INDEX EVOLUTION AND GENETICS 99

Ffactor VIII, 88fertility, 53finger, 34, 35fire, 44, 45, 47fish

bony, 28, 37cartilaginous, 36Devonian Period, 28eels, 27evolution, 28first appearance, 20freshwater, 28Lepidotus, 20reproduction, 29, 36

fluorescence, genetically modified rats, 89food, genetic modification, 86-87forensic science, 84-85fossil

analysis, 10-11Burgess Shale fossil bed, 26importance, 20oldest, 18, 21, 24-25See also types of organisms, for example,

dinosaurfounding effect, 13France, cave painting, 51Franklin, Rosalind, 60fungus, 37

Ggender, 74, 90gene, 58, 64-65

cloning, 86DNA markers, 72-73engineering: See genetic engineeringheredity, 65, 66human genome, 74-75number, 75traits, 66

gene therapy, 5, 82-83Genesis, 9genetic code, transcription, 62

See also DNA; human genomegenetic disease, 82-83genetic drift, 13, 91genetic engineering

animals, 88-89antibiotics, 70-71biochips, 80-81BioSteel, 89cloning, 78-79, 86gene therapy, 82-83insulin, 66, 70-71pharmaceuticals, 70-71, 88-89plants, 86-87recombination, 70-71stem cells, 76-77

genetic flow, 13genetic microarray, 80genetic mutation, 10, 12, 13, 16, 90-91genetic recombination, 70-71genetic variation, 12genetically modified food, 86-87genetics, 64-65, 66-67

chromosomes, 56, 57human genome, 5, 74-75, 90Mendelian laws of inheritance, 67tracing, 90

genome: See human genomegenome sequencing, 75geometric moth, 12-13Giganotosaurus carolinii, 21, 31giraffe, 12glaciation, 21golden rice, genetically modified food, 87golden thread spider, 89golgi body, 23Gondwana, 21gorilla, 40, 42gray wolf, 16guanine, 60, 61, 85Gurdon, Sir John, 74gymnosperm (plant), 36

genome: See human genomemigration, 45muscle, 41origins, 4, 21, 48-49phylogenetic tree, 40-41primates, 34-35: See also primateskulls, 4speech, 40-41

human evolutionagriculture, 53analysis, 11archaeological findings, 42-43, 45art, 50-51beginnings, 4, 38-39bipedalism, 42brain, 40, 44building, 51cities, 52-53culture and society, 50-51, 52-53dorsal spine, 42environmental adaptation, 42fire, 44, 45, 47hominins, 40Homo erectus, 45hunting, 46-47Ice Age, 47migration, 44, 49Neanderthals, 46-47phylogenetic tree, 40-41religion, 52skeletal structure, 42speech, 40-41, 50tool use, 44, 46-47, 51tracing, 90weapons, 51writing, 53

human genomedefined, 74diseases, 74-75importance, 5, 74, 90Sanger Method, 75

Human Genome Project, 66hunting, 46-47hybridization, 16hypoallergenic cat, 89

IIce Age, 47India, 8inheritance, 64-65, 67

See also genetics; heredityinquilinism, 14insect, 37insulin, 70-71invertebrate, 24

Burgess Shale fossils, 26-27mollusk, 36sponge, 26worm, 14, 86-87See also arthropod

Islam, 9

JJeffreys, Sir Alec, 84jellyfish, genetically modified rats, 89Judaism, 9Jurassic Period, 21, 31

KK-T boundary, 32karyotype, 58Kimberella, 25kudu (mammal), 15

Llanguage, 40-41, 50Laurasia, 20lava, 20law of independent assortment, 67law of segregation, 67

laws of inheritance, Mendelian, 67Lepidotus, 20life

origins, 20, 22, 36tree of life, 36-37

lion, 15lizard, 37Lucy, early hominins, 43lysosome, 23

Mmammal

buffalo, 14cat, 89characteristics, 37chimpanzee, 42cow, 78-79dog, 17earliest mammals, 21, 30evolution, 34-35giraffe, 12gorilla, 42gray wolf, 16kudu, 15marsupial, 34, 37monkey, 34, 35, 42number of species, 37pig, 88-89rat, 89reproduction, 36sheep, 66, 78skeletal design, 10Triassic Period, 30wolf, 17zebra, 15

mammaliaformes, 34Marella, 27marsupial, 34, 37mass extinction, 20-21, 32-33mawsonite, 25Meganuera, 28medicine

biochips, 80-81

HHallucigenia, 27haplogroup, 91hemophilia, 88-89Hennig, Willi, 37heredity, 54-55, 65, 66-67hermit crab, 14herpesvirus, gene therapy, 82Hinduism, 8Hipparion, 19hominin, 42-43

beginnings, 21, 40evolution: See human evolutionmigration, 42, 45

Homo erectus, 40-41, 44, 45, 49Homo habilis, 21, 40, 44, 45Homo heidelbergensis, 46, 47Homo neanderthalensis (Neanderthal), 21, 39,

41, 46-47, 48Homo sapiens, 38-39

builders, 51Cro-Magnon, 48-49earliest, 91evolution, 41: See also human evolutionmigration, 49Neanderthals, 21, 41, 46-47, 48skeletal structure, 42See also human

Homo sapiens sapiens, 50, 51See also human

honeycreeper (bird), 16human

ancestors, 34-35, 48-49, 90bones, 41brain, 4chromosomes, 56classification, 37creation, 8-9culture, 50-51, 52-53defined, 8earliest, 42, 48, 91environmental adaptation, 42evolution: See human evolution

100 INDEX

gene therapy, 82-83stem cells, 76-77

meiosis, 54-55, 64, 65men, 74, 90Mendel, Gregor, 64, 65, 66-67Mendelian laws of inheritance, 67, 72Mesopotamia, 53Mesozoic Era, 21, 30-31, 34messenger RNA (mRNA), 58, 62-63metabiosis, 14Metaldetes, 20metaphase, 64, 65meteorite, Chicxulub, 32-33microevolution, 12microsatellite, 72Miescher, Johann Friedrich, 66Milky Way, 33mitochondria, 23, 90mitochondrial DNA, 11, 74, 79, 91Mitochondrial Eve, 49, 90mitosis, 54-55, 56, 58, 76molecular evolution, 22molecular genetics, 66mollusk, 21, 36monkey, 8, 34, 35, 42

See also primatemonotreme, 37Morgan, Thomas Hunt, 57, 64, 65, 66Morganucodon, 34moth, pollution and adaptation, 12Mullis, Kary, 75multicellular organism, 24-25, 26-27multiregional evolution, 49muscle, 41muscular dystrophy, 82mutation: See genetic mutationmutualism, 14myriapod, 37myth, 8, 9

Nnatural selection, 10, 12, 15Neanderthal (Homo neanderthalensis), 21, 39,

41, 46-47, 48nematode, 75Neogene Period, 34Neolithic Period, 5, 52nucleic acid, 23

See also DNAnucleoplasm, 23nucleosome, 59nucleotide, 60, 61nucleus (cell), 23, 56-57, 64-65, 76, 78

OOlduvai (Tanzania), fossil skull, 45opposable thumb, 34orangutan, 40Ordovician period, 28ovule, 78, 90oxygen, 20, 21, 26

Ppainting, cave, 50-51Paleogene Period, 32, 34Paleolithic art, 50-51Paleozoic Era, 20, 28-29Pangaea, 20, 30, 31Paranthropus, first hominids, 43parasitism, 14pea, Mendelian genetics, 66Permian Period, 29, 30petrified fossil, 10-11pharmaceutical, 88-89phoresy, 14phylogenetic tree, 36-37, 40-41phylogenetics, 91

pig, genetic engineering, 88-89Pikaia, 27placental mammal, 34, 36, 37plant

beginnings, 23Cenozoic Era, 34classification, 37defined, 36evolution, 35pollen, 29reproduction, 32Silurian Period, 20terrestrial adaptation, 28, 29transgenic, 86types, 36water transport, 29

plasmid, 70, 86, 87Plateosaurus, 30Pliocene Epoch, 38-39pollen, 29polymerase chain reaction (PCR), 72, 75, 85polymorphism, 73polypeptide, 63population, genetic flow, 13power of exclusion (PE), forensics, 85prairie, 21Precambrian Era, 20, 24-25predation, coevolution, 15prehensile thumb, 34priapulid (worm), 26primate

chimpanzee, 42earliest, 34-35evolution, 40gorilla, 42humans, 37: See also humanspeech, 40tail, 35See also monkey

prokaryote, 22, 23, 24, 58-59prophase, 64, 65protista, tree of life, 37

RRanunculus (plant), 35rat, 89recessive allele, genetics, 66recombinant DNA, 70-71regional continuity, 49religion, 8, 9, 52reproduction, 36reptile

dinosaur: See dinosaurearliest, 28-29Jurassic Period, 31prominence, 21types, 37

restriction enzyme, 86ribonucleic acid: See RNAribosome, 23, 62, 63rice, golden, 87RNA (ribonucleic acid), 58, 62-63, 83rodent, 34, 89rosette, 58, 59

SSanger, Frederick, 75Sanger Method, human genome, 75selective breeding, 17sex chromosome, 74sex-linked inheritance, 64-65sexual reproduction, 36sight, 34Silurian Period, 20, 28-29single-celled organism, 20, 23, 36, 58

See also bacteriaSistine Chapel, 9skeleton, 10skull

Australopithecus, 4Cro-Magnon, 5, 48human, 4Neanderthal, 47

Tuang, 42snake, 37society, 52-53somatic-cell nuclear transfer, 78-79Spain, cave painting, 51speciation, 16-17species

chromosomal number, 57coevolution, 14-15mass extinctions, 20-21, 32-33number of animals, 37speciation, 16-17

speech, 40-41, 50spermatozoon, 90spider, recombinant silk, 89spine, 42sponge, 26Stegosaurus, 31stem cell, 76-77stromatolite, 19, 20, 24symbiosis, 22

Ttail, 35Taung, skull of, 42telophase, 65tetrapod, 36Thylacosmilus, 21thymine, 60, 61Titanis, 19, 21tool

Cro-Magnons, 48 earliest creation and use, 44Homo sapiens sapiens, 51Neanderthals, 46

transfer RNA (tRNA), 62-63transgenesis, 88-89transgenic animal, 88-89transgenic bacteria, 87transgenic food, 86-87transgenic plant, 86Triassic Period, 21, 30

tribrachidium, 25Turkana Boy, hominin remains, 45Turkey, 52turtle, 37

Vvacuole, 23Venus of Willendorf, 51vertebrate, 36vision, 34volcanic eruption, mass extinction theories, 33

W-ZWalcott, Charles, 26Waldeyer, Wilhelm von, 66Watson, James, 60, 66weapon, 51wolf, 17women, 74, 90worm, 14, 86-87writing, 53X chromosome, 74Y chromosome, 74, 90Yoruba mask, 8zebra, 15


Bisl 05 evolution and genetics

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