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Sources of Evidence for Evolution 1. Fossils • Sedimentary rock with fossils shows the kinds of species that were alive in past. • This history of life captured in rock is called the fossil record. Evidence from the Fossil Record • Fossils in young layers of rock are more similar to species alive today as opposed to fossils found in older layers of rock. (eg. evolution of the modern camel) • Fossils appear in chronological order in rock layers. • Not all organisms appear in the fossil record at the same time. (eg. fish are the 1st vertebrates that appear) Evidence from Transitional Fossils • These fossils show intermediary links between groups of organisms. • Have helped scientists the process • of evolution and relationships between groups of organisms. • Link the past with the present. • Allow scientists to identify vestigial structures (structures that are the reduced form of structures in an organism’s ancestors) • See Fig 8.7 on pg 335 2. Biogeography • Defined as the study of the past and present geographical distribution of organisms. Evidence • Geographically close environments are more likely to be populated with related species. • Animals found on islands often closely resemble organisms on the closest continent. • Fossils of the same species can be found on the coastlines of neighbouring continents. • Closely related species are almost never found in exactly the same location or habitat. 3. Anatomy • Homologous structures have similar structural elements and origin but may (or may not) have a different function. (eg. hair in mammals) • Organisms that share a common ancestor will show homologous structures. (see Fig 8.9) • Functional similarity in anatomy does not mean that those species are closely related. (eg. wings in insects, birds, bats and pterosaurs all serve the same function but show no structural similarities) Homologous Structures Analogous Structures – Analogous structures have similar functions even there the organisms do not share any common evolutionary origin – Some species of different origins have similar physical structures (convergent evolution) – Example1: the wings of bats and insects – Example 2: the eyes of vertebrates, molluscs (like squid and octopus) and insects 4. Embryology • The study of early pre-birth stages of an organsim’s development. • The similarities between embryos in related groups (eg. vertebrates) provide evidence for a common ancestral origin. • See Fig 338 5. DNA • Evolutionary relationships between species are reflected in their DNA. • Scientists can determine how related 2 organisms by comparing the similarities in their DNA. • Similar patterns in 2 organisms DNA must have been inherited from a common ancestor. • Gene sequences have determined that dogs are related to bears and that whales and dolphins are related to ungulates (i.e. cows and deer) Read pg 339 and answer the ? HW • pg 340 #1, 2, 5-7, 11, 15