The tree of life. It seems not many people know what it really means…Every living thing on this planet is related through millions of years of evolution

  ("What Is The Evidence For Evolution?")

By Oliver Small

The Theory of EvolutionIN recent history, the theory of evolution has been very controversial as it explains the origins of life differently to how the Bible explains it. Due to this, many people are still misinformed and uneducated on a theory that is widely accepted in all fields of science and so through this article I will attempt to explain, with evidence, the theory of evolution.

Definition of Biological EvolutionEvolution is the cornerstone of modern biology as it unites all fields and provides an explanation to how all species have arrived to the point they are at now. Simply put, biological evolution is “descent with modification” ("An Introduction To Evolution"). This means that as a species keeps creating offspring, the population as a whole and the gene pool changes to suit the environment. The theory of evolution also states that every living thing descended from one common ancestor. Usually the process of evolution is very slow - taking thousands of years - and is called Macroevolution but there are cases of drastic

change in short time periods called Microevolution. Within evolution there are mechanisms that drive it such as Natural Selection and Speciation. There are also ways to back up the theory such as palaeontology, genetics, geology and astronomy. We will cover these topics in the text to come.

Natural Selection – What is it and how does it relate to changes in a population?“Natural selection is the only mechanism of adaptive evolution” ("Natural Selection") and it means that over time the traits of a species change to become more resilient to their environment. This occurs because a certain trait is gained by some of the population by mutation, genetic diversity or other means and they end up living longer meaning that trait is favoured. Because the organisms with the favoured trait live longer, they create more offspring and therefore pass on that trait. Eventually, organisms without the favoured trait die out as they are more susceptible to the environment and don’t make as many offspring, thus, evolving the species.

A great example of this process is the Peppered Moth during the Industrial Revolution. At the beginning of the revolution most of the population were white and spotted except for 2%, which were dark coloured. The white moths could easily disguise into the white coloured trees and were seen less often by birds. Throughout the revolution, factories were built that spewed out massive amounts of soot into the air coincidentally covering a large amount of the previously white trees, turning them into a deep black colour. At this point the black moths had the advantage and blended in with the trees more, making the white moths stand out and eaten by birds at a younger age. This meant that the dark moths lived until they could have offspring, passing on the gene to the next generation and by 1895 black moths consisted of 95% of the population.

Natural selection is evident today and a big issue in the form of antibiotic resistant bacteria. Antibiotics were a huge development in the field of medicine when it was discovered because it kills bacteria and stops diseases that are associated with them. The issue is that some bacteria are no longer affected by it. This is caused by natural selection as some bacteria are left behind after taking the drug that gives them some resistance to it; they then multiply which passes the resistance on. The process repeats and the bacteria become more and more resistant until antibiotics have no effect at all. Obviously this is very

worrying because we heavily rely on antibiotics to kill off bacteria in order to treat sick people.

Speciation – What is it?

First of all, what is a species? Some might say it is a group of organisms that all look the same but in actual fact it has a very specific definition and for good reason. It is defined as a group of organisms that can interbreed and create fertile offspring. It is very important that they can make fertile offspring because members from two different species can breed but their offspring won’t be able to have children themselves, as they don’t require the genetic information to do so. An example of one of these hybrids is a liger – a cross between a lion and a tiger. Sometimes one species can split into two over time and this is called speciation. Allopatric (from the Greek ‘different countries’) speciation is where a physical barrier, such as a mountain or ocean, separates a species and through natural selection each group adapt to each of their environments. Eventually, over the course of thousands of years the two groups of organisms will become so different due to natural selection that they won’t be able to create fertile offspring together and by definition are two new species. Sympatric (from the Greek ‘same country’) speciation is similar to allopatric speciation except there is no physical barrier but instead a reproductive barrier. This is the rarer of the two but can occur if a subset of a population changes their behaviour for environmental reasons or other means which then start to, through natural selection, change into a new species.

How do genes and environmental factors interact to affect the survival of organisms in a population?The genetic traits of an organism are extremely important for it to survive. If a species can’t handle the environment that they live in then the species would either go extinct or evolve and adapt. When environmental factors change rapidly in an environment such as a drought, flood, deforestation, increase in predators etc. it is usually the case that the species will suffer from a loss of numbers because they can’t adapt quick enough. However, if any do survive then they will pass on traits that make the species as a whole be able to survive more significant and rapid changes.

The Fossil Record - How does it relate to the age of the earth and how does it relate to how long life on earth has been evolving?The fossil record is the collection of all fossils found and was one of the first clues given to lead to the theory of evolution as the findings suggest that different animals existed when

the earth was a lot older. The Oxford Dictionary defines a fossil as “The remains or impression of a prehistoric plant or animal embedded in rock and preserved in petrified form.” One thing that the fossil record shows is the gradual change of simple species to more complex ones we see today. We can do this by dating the fossils using techniques such as carbon dating and then relating it to other found fossils. The more recent the rock is the more the structure of the fossil looks like the organisms we observe today for example, in rocks 1 billion years old there are only fossils of single-celled organisms and at 230 million years ago mammals started appearing. Of course, the fossil record does not contain every organism to ever live but provides substantial evidence of the theory of evolution.

What dating methods do scientists use to interpret the fossil record and how do they work?Dating a rock is imperative in order to know the order of evolution that organisms went through so we can fill out the tree of life properly. Dating rocks is split into two categories – one more accurate than the other. First is relative dating, which is quite inaccurate, but it is free. It basically consists of eyeballing two different rocks, comparing them, and then deciding which one is older than the other. As you might be able to imagine, that technique is not very accurate and so this is where absolute dating comes in handy. Three ways this can be achieved is radiometric dating, dendrochronology and the molecular clock. Any radioactive material has a half life where half of any given amount of it will decay in a set period of time e.g. the half life of carbon-14 is 5730 years. This is the basis of radiometric dating where the atoms of a radioactive substance are counted in the rock and from that information its age is calculated. Similarly, the molecular clock uses biomolecules and their rate of mutation to compute how old it is and finally dendrochronology is the counting of rings in a tree stump to tell its age.

How do we know that evolutionary theory is accurate?The evidence for evolutionary theory is quite overwhelming that it is unbelievable that some people don’t accept it as fact. There are four fields of biology that contribute the most to this evidence; comparative anatomy, embryology, palaeontology and DNA comparisons. Comparative anatomy is where you look for similarities and differences between species and the more similar two species are to each other the more probable that they are closely related. For example you might compare how whales give live birth just like other mammals. Embryology is similar to comparative anatomy but it is studying the similarities and differences when the organism is still at the embryo stage. This is where seemingly farfetched similarities between species are discovered like how whales

have nostrils on the front when they start life but they it migrates to the top to create blowholes. Palaeontology is a fairly obvious one but it is the study of comparing fossils found from different time periods to the organisms we see today. Finally, with the recent advances in genetics it is possible to see exactly how similar the DNA of one species is to the DNA of another. This is the most accurate and can even date how long ago the common ancestor of both species existed. E.g. we share 98.6% identical DNA to chimps and our common ancestor existed around 13 million years ago.

A case study of evolution having occurredThrough the fields described above I will show you a study of the evolution from land mammals to whales, as we know them today.

Comparative anatomyWhales are mammals and is backed up by the fact that they give live birth, feed milk to their young, are warm blooded and they don’t have gills like fish but breath using lungs and blowholes on the tops of their heads. The blowholes on their heads are very interesting as in the skulls of all cetaceans there are two nasal passages, which is a sign that it could be a modified nose from a land mammal. They’re flippers also have all the same bones that would be found in the arms of land mammals and there are bone remnants where you would expect legs to be that resemble hip, thigh and shin bones.

EmbryologyWhen you put a whale and human embryo side-by-side you can see astonishing similarities such as arm and leg nubs. Another interesting thing is that with dolphins (another member of the cetacean family which whales are a part of) their nostrils are at the front of their head to start with and then slowly migrate to the top of their head to form a blowhole.

PalaeontologyMany things can be learnt from a Prozeuglodon’s fossils such as a blowhole that is halfway up the face showing and intermediate stage in the migration of the blowhole and suggesting evolution. Also, this species has very small but fully functioning hind legs. The Maiacetus Inuus was a species that existed 47.5 million years ago and is very had to tell that it is a whale by looking at it. It is classified as one because all of the fossils were found near other sea creatures and because they had flattened finger bones suggesting they were strong swimmers and had webbed feet. The hind limbs of this species are large enough to be able to support its weight suggesting it could roam both the water and land.

DNA ComparisonThe DNA of a whale has been examined against a variety of animals including the hippopotamus, which happens to be its closest relative genetically. This tells us that they both evolved from a common ancestor that lived around 54 million years ago. Although

being very different on the outside, there are similarities that were discovered that back up this find. An ancient whale ankle bone is similar to the ankle bone of a hippo and is very rare in other species, both whales and hippos have chambered stomachs which is common for herbivores but uncommon for carnivores and they both have internal testicles.

Hopefully by the end of this article you have a greater understanding of the most widely accepted reason to the origins of life and are able to see how compelling the evidence is.