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Biol 121 225 Freeman 484-490 Evolution 2- Ch. 24

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University of British Columbia
BIOL 121

Biol 121 225 Freeman 484-490 Mar 8, 10 Evolution 2- Ch. 24, Evidence for Evolution Main points of Darwin’s theory? 1. Evolution – “descent with modification” -all organisms have a common ancestor – Linnanean hierarchy, “tree of life” -two species in a family are more closely related than those in different families in the same class -the environment changes traits in a population over time/over generations (allele frequency changes in a population) 2. Natural selection – the mechanism of evolution Premises: -genetic variation exists -performance affects reproductive success  higher fitness -competition  differential survival -natural selection occurs through interaction between environment and existing genetic variation in a population -it causes a change in the population resulting in increase in those better suited for survival -variable population because of adaptation of population to environment variation + selection = adaptation Evidence for evolution -the fossil record 1) Evidence for change through -extinct species can be noticed in fossils containing shells, bones, leaves, bird tracks, time dung, etc a) Fossil record -this was used as evidence by Darwin who then said that species were not static, i) Extinctions immutable entities -his reasoning: since species have gone extinct, array of species living on Earth changes over time ii) Transitional forms -when a species evolves over generations, it may enter many transitional forms -transitional form = fossil species with traits that are intermediate b/t those of older and young spp. -was known as the “law of succession” when there were resemblances b/t fossils found in rocks underlying certain regions and the living spp. found in the same geographic area E.g.whales -Evolution of whales: Whales evolved from terrestrial mammals to the aquatic mammals of today -transitional forms had shorter legs with time, as well as a flatter body -eventually, legs disappeared and became small fins b) Changes in living organisms -a vestigial trait is a reduced or incompletely developed structure that has no function i) Vestigial trait or reduced function, but is clearly similar to functioning organs or structures in closely related species -for example, humans have tailbones (coccyx) but we don’t have tails -also, appendix in human is reduced version of cecum – digestive organ in other species ii) Artificial selection
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