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Evidences for Evolution The earth is about 4,600 million (or 4.6 billion) years old. The first signs of life appeared about 3,800 million years ago. We can see evidence of evolution all around us. We can observe: Similarites in all living things that suggest descent from a common ancestor Differences between living things in the same family that suggest change over time (evolution) 1. Fossils – the remains of living things, found in sedimentary rocks, are simpler the older (deeper) they are. Fossil species are similar to but differ from today’s species. The evolution of many modern day species can be traced very fully e.g. elephant, horse. New fossil types mark a change in the environment. Transitional forms link past and present. 2. Biogeography – the study of the distribution of species shows animals on islands resemble species from the nearest mainland. 3. Comparative Anatomy – comparing body structures of different species shows homology (similar construction due to a common ancestor). E.g. pentadactyl limb of mammals and birds. Vestigial organs show remnants of once useful parts e.g. kiwi’s wing. 4. Comparative Embryology –shows related animals (e.g. vertebrates) often have similar stages in their embryonic development. 5. Molecular Biology – All species share a common genetic code, suggesting all forms of life are related to some extent through branching evolution from the earliest organisms. Similarity in DNA sequences and amino acid sequences in proteins such as cytochrome and haemoglobin also suggest common ancestry. 6. Artificial Selection – As farmers selected the best plants and animals to breed from they have changed their form over time, getting bigger and better suited to the environment they are living in. 7. Contemporary Examples – evolution of antibiotic-resistant bacteria, DDT-resistant insects, mutants of HIV resistant to new drugs etc. Evolution is not a theory, it is a fact. Evolutionary theory is about the mechanism by which this change occurs.