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QUESTIONS: 1) How do changes in DNA affect the organism they occur in? 2) What are the major mechanisms that drive evolution? 3) What is speciation and how does it occur? EVIDENCE OF EVOLUTION “They’ll laugh as they watch us fall, The lucky don’t care at all, No chance for fate, It’s unnatural selection, I want the truth” Muse, Unnatural Selection GENETIC EVIDENCE Organisms which are more closely related share more of the same genes Therefore, it is most likely that these organisms arose from a common ancestor possessing those genes, and thus acquired them from a common source It is unlikely that these genes would have arisen independently in various organisms MOLECULAR EVIDENCE Similarly, structural elements that make up related organisms are conserved, as from a common ancestor The structure of proteins within the cell will tend to remain the same, unless a mutation produces a more favourable variant This means that organisms are related not only on a physical level, but on a molecular level. MATHEMATICAL INTERLUDE Take a small protein, 50 amino acids long Each amino acid is coded by 3 nitrogenous bases Each base needs to be a specific one in order to generate the proper amino acid (mostly, there is some flexibility), and has a ¼ probability of being that amino acid Thus, there are 4^(3x50) possible combinations = 2.0 x 1090 4.9 x 10-91% chance of occurring at random That is a 0.000000000000000000000000000000000000000 00000000000000000000000000000000000000000 000000000049% chance Repeat this for every protein that is conserved, many of which are MUCH larger than 50 amino acids long ANATOMICAL EVIDENCE There are many physical structures which have clear descent from a common ancestor These are called homologous structures, and tend to be common in organisms which are related If the similarity is not apparent in the adult versions of an organism, then it may be necessary to observe the embryonic structure FOSSIL EVIDENCE You can trace an organisms evolution by following its progress through the fossil record Fossils will occur in sequences of increasing complexity and diversity, indicating that organisms were evolving to become more adapted to their surroundings Key fossils especially include those known as “missing links”, which provide bridges between ancient ancestors and more modern creatures