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Darwin’s Theory of Evolution Chapter 16-3 Image from: Biology by Miller and Levine; Prentice Hall Publishing©2006 A.Darwin Presents His Case • In 1859, On the Origin of Species presented evidence and proposed a mechanism for evolution that he called NATURAL SELECTION http://www.loc.gov/exhibits/world/images/s125.jpg B. HIS CONCLUSIONS 1. GENETIC VARIATION (differences) is found naturally in all populations http://www3.nationalgeographic.com/animals/images/primary/zebra-herd.jpg 2. Any inherited characteristic that increases an organism’s chance of survival = ADAPTATION http://www.wildlife-traps.com/skunks.html http://www.atomtigerzoo.com/photos/images/20060421233733_duckfeet.jpg http://www.3kitty.org/travelrama/Photos/123-21-4x6.jpg GALAPAGOS FINCHES http://images.encarta.msn.com/xrefmedia/aencmed/targets/illus/ilt/T014608A.gif The _____ beaks of Galapagos finches have adapted ______ to eating a variety _____ of foods _____. 3. STRUGGLE FOR EXISTENCE means members of each species must compete for food, space, and other resources. http://www.wasatchcomputers.net/gallery/elk_fight.jpg 4. SURVIVAL OF THE FITTEST organisms which are better adapted to the environment will survive and reproduce, passing on their genes. http://www.poster.net/bedard/bed202.jpg http://www.cartoonstock.com/newscartoons/cartoonists/cga/lowres/cgan170l.jpg 5. Ability of an individual to survive and reproduce in its specific environment fitness = ___________ C. DARWIN’S THEORY Over time, NATURAL SELECTION results in variation in inherited characteristics of a population. These changes increase a species’ fitness in its environment. How Does Evolution Really Work? DESCENT WITH MODIFICATION - suggests that each species has descended, with changes, from other species over time. - this idea suggests that all living species are related to each other and share a common ancestor. D. Evidence of Evolution HOMOLOGOUS Structures 1._____________________ Similar features that originated in a shared common ancestor Image from: http://www.angelfire.com/ab7/evolution12/evolutionclues.html Ex: limbs of vertebrates, look very different, but are made from the same bones because they are made from the same clump of embryonic cells. EMBRYOS OF DIFFERENT VERTEBRATES Image from: http://www.angelfire.com/ab7/evolution12/evolutionclues.html 2. VESTIGIAL Structures Some homologous structures are vestigial & have no useful function even though they are still present. Ex: like hipbones in whales http://www.txtwriter.com/backgrounders/Evolution/EVpage12.html Ex: In humans, the cecum is shrunken and unused. In ancestors used to digest plants. It is our appendix. http://www.medicalgeo.com/images/appendix.gif 3. ANALAGOUS Structures serve identical functions and look somewhat alike ex: wings of bird & insect Differ greatly in anatomy Can infer wings evolved independently & share a very remote ancestor http://www.suite101.com/files/topics/6234/files/tail_HumanTail.gif PBS EVOLUTION VIDEO CLIPS Isn’t Evolution Just a Theory? QuickTime Who was Charles Darwin? QuickTime How Do we Know Evolution Happens? QuickTime How Does Evolution Really Work? QuickTime | Why Does Evolution Matter Now? QuickTime Why is Evolution Controversial Anyway? QuickTime 4. Molecular Biology -Similarities in DNA sequences provide evidence of common descent -Universal genetic code Image from: BIOLOGY AP EDITION by Campbell and Reece; Prentice Hall Publishing©2005 Human- 46 chromosomes Chimpanzee- 48 chromosomes -Similar karyotypes suggest an evolutionary relationship. • Homologous Proteins – share structural & chemical (amino acid) similarities between species