Evidence for Evolution Evidence for evolution overview

Scientists have discovered a heap of evidence concerning the evolution of a species. The evidence comes in many forms; from old techniques such as fossils and studying similarities between related living organisms to more modern day techniques such as DNA testing.

FOSSILS Fossils are preserved remains or impressions left by organisms in the past.

Most fossils are found in sedimentary rock, which form strata (bands of rock) containing fossils embedded in sediment. Watch the video and take notes Fossil formation

Fossils provide a unique view into the history of life by showing the forms and features of life in the past. They tell us how species have changed across long periods of the Earth’s history. Evolution of the whale

Transitional fossils = fossils than show transitions in evolution

COMPARATIVE ANATOMY Homologous structures The image below shows that there is a remarkable resemblance between the limbs of a variety of animals, despite the fact that they are all used very differently. This is because they all have a common ancestor and this is known as homology. They have homologous structures. (Divergent evolution) The pentadactyl limb

This provides evidence for evolution because it shows us they have all come from a common ancestor. Homologous structures are evidence for evolution because it wouldn’t make sense for all of their basic bone structures to be the same when they all have such different functions, would it?! Homologous structures = same structures + different functions

Don’t get homologous structures confused with analogous structures Don’t get homologous structures confused with analogous structures! Analagous structures are those that have the same function, but they are not derived from a common ancestor and have undergone different forms of development. (Convergent evolution)

An example of analogous structures are the wings of a butterfly compared to the wings of a bird and the wings of a bat. The function of the wings is to enable both these animals to fly. The structure of them is what sets the two apart. There are no bones underlying the wing of the butterfly. Analogous structures = same function + different development patterns

MOLECULAR BIOLOGY DNA-DNA hybridisation is a technique used to see how closely related different species are. This is a molecular biology technique that measures the degree of genetic similarity between polls of DNA sequences. It involves splitting DNA, using heat, and merging strands from different species (form a ‘hybrid’) to look for differences in the chains. The more closely matched the strands the base pairs are, the stronger the binding in the strands. Also, the lower the temperature at which hybrid DNA strands separate as compared to the original species, the less similar the two species are.

Mitochondrial DNA (mtDNA) analysis provides evidence for how closely related the organisms/groups are and their times of divergence. mtDNA is found only in the mitochondria of cells (and not the nucleus of cells). Therefore, it is not subject to the processes of meiosis and crossing over. Mitochondria are strictly maternally inherited, with no recombination of alleles. Mitochondria remain in the cytoplasm of egg cells so are passed on when the egg is fertilised.

Once a mitochondrial mutation occurs in the germ cell of the female, the mutation is transmitted to all of her offspring; maternal lineages can be traced back in time and can allow of identification of a common ancestor, and likely times of divergence of individuals/groups.

Overview of Evidence for Evolution