4.3.5 evidence for natural selection

term used to explain how features of the environment apply a selective force on the reproduction of individuals in a population

• naturalist • spent much of life studying & observing living organisms • proposed mechanism for evolution = natural selection • theories developed during 5-year trip on HMS beagle • visited galapagos islands where many species on each island were similar but had clear variation eg. wide variety of bird species was actually closely related finches • published ‘the origin of species’

• naturalist • independently came to same conclusions as darwin • collections in south east asia & amazon • darwin & wallace first publication = joint papers together on subject of evolution by natural selection

• offspring generally appear similar to their parents • no 2 individuals are identical • organisms have ability to produce large numbers of offspring • populations in nature tend to remain fairly stable size

• there’s a struggle to survive • better-adapted individuals survive & pass on characteristics • over time, a number of changes may give rise to new species

• fossil evidence • biological molecules

• in the past, the world was inhabited by species different from those today • old species have died out & new species have arisen • the new species that have appeared are often similar to older ones found in same place

• certain molecules are found throughout living world –> if 1 species gave rise to another, both are likely to have same biological molecules which suggests all species arose from 1 original ancestor • 2 closely related species will have separated only relatively recently –> their bio molecules likely to be identical/very similar • in species which took separate evolutionary paths a while ago, the biological molecules are likely to differ more • evidence from molecules eg. cytochrome c & other proteins (show pattern of changes)

• 1.2% of coding sequence different from chimpanzees • 1.6% different from gorillas • 6.6% different from baboons