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Transcript
Monday, February 13th Proofs of Evolution Chapter 21 Darwin’s Theory of Evolution • Darwin studied Finches on the Galápagos Islands. • Each bird had seemed to perfectly match the specifics of the island it was on Modern Day Research Humans Influence Evolution Intro to Fossils, Types • • • • Specimens preserved in amber Siberian permafrost fossils Dry cave fossils Your typical rock fossil Quick overview of Rock Fossils • First, the organism is buried in sediment • Secondly, calcium is mineralized • Lastly, the surrounding sediment hardens to form rock 2 Ways to Date Fossils • People in Darwin’s time used relative dating – dated rocks by their position with respect to one another (which layer was on top of which other layers?) 2 Ways to Date Fossils • Today we can use radioactive decay and use absolute dating to determine the age. • Half-Life – amount of time needed for onehalf of the original amount to be transformed • Once a rock is formed, no radioactive isotopes can be added, so we can compare the daughter isotope to the original, determine how many times it has halved, and date the sample. How are Fossils used as Evidence for Evolution? • Once the fossils are lined up from oldest to youngest, they show evidence of successive evolutionary change. • Prokaryotic (no nucleus) eukaryotic fishes land dwelling organisms dinosaurs humans The Gaps in the Fossil Record • As previously stated, fossils rarely form. Because of this, when we line up all the fossils by age, there are still large gaps between one organism and the next. • There are still enough intermediate forms of organisms available to show the major transitions of evolution on Earth To this Day we still find Transition Fossils • For a while we didn’t have any fossils that showed the transition from hoofed land animals to modern day whales • But we were able to find some that helped show the transition Evolution of the Horse • • • • Evidence from fossils show the horse’s: a. Change in body size b. Decrease in toes c. Change in teeth to accommodate browsers to grazers Homologous Structures • As vertebrates have evolved, the same bones have sometimes been put to different uses • Homologous Structures – structures with different appearances and functions that all derived from the same body part in a common ancestor • Natural selection has modified the same initial starting blocks to serve very different purposes. Embryonic Development • Comparing how organisms develop also shows strong evidence supporting evolution • http://www.youtube.com/watch?v=h3Lkac89 0c0 Vestigial Structures • Vestigial Structures – structures that have no apparent function, but resemble structures their ancestors possessed. • Example: Humans have muscles to “wiggle” our ears • These muscles allow other mammals to move their ears to pinpoint sounds.. but for us… these muscles don’t have much use Vestigial Structures • Boa Constrictors have hip bones and rudimentary hind legs • Whales have bones that resemble pelvic bones of other mammals, but are weakly developed and have no apparent function Vestigial Structures • These structures were helpful or useful to an organism’s ancestor, but not for them. This is used to prove descent with modification, or evolution Convergent Evolution and Biogeographical Record • Biogeography – study of the geographic distribution of species • Reveals that different geographical areas sometimes exhibit organisms of strikingly similar appearance even though the organisms may only be distantly related • Why do some organisms that don’t live near each other, and aren’t closely related, sometimes have similar body structures or forms? – Convergent Evolution Convergent Evolution • Convergent Evolution – selection can tend to favor parallel evolutionary adaptations in similar environments