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Darwin’s Theory of Evolution
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Historical Context (early 1800s) Aristotle, Judeo-Christian culture, book of Genesis… – The earth is only 6000 years old – All living species are “static” (put here ‘as is’)
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Pre-Darwin Lamarck (early 1800s) Buffon Inheritance of Acquired Characteristics
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Inheritance of Acquired Characteristics Why do giraffes have long necks? Because they stretch them during their lifetime, then their offspring have long necks The theory of “Use & Disuse”
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Who was Darwin? Surgeon in training Minister Recruited by captain of HMS Beagle Set sail in 1831 at the age of 22
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Not just the Galapagos…
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Not just finches…
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Darwin made 3 main observations… 1. Members of a population vary in their physical traits. 2. Many physical traits are inherited from parent to offspring. 3. All species are capable of reproducing more offspring than the environment can support.
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And drew 2 conclusions: 1. Individuals who inherit traits that give them a better chance of surviving tend to leave more offspring than other individuals 2. This unequal reproduction of offspring causes ‘favorable’ traits to accumulate in a population over generations. (“survival of the fittest; struggle for existence)
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Darwin called these conclusions “Descent with Modification” We call it “Natural Selection”
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Important!! What is ‘favorable’ in one environment may not be in another environment. The environment determines what is favorable and unfavorable.
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4 Take-home Points about Natural Selection 1. Individuals DO NOT evolve. Evolution refers to generation-to- generation changes in a population. 2. Natural selection can only amplify or diminish traits that are inheritable.
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4 Take-home Points about Natural Selection 3. Evolution is NOT goal-directed. No notion of “perfect species.” Environmental factors vary in place & time…’favorable’ traits will also vary.
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4 Take-home Points about Natural Selection 4. Evolution is about compromise.
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It’s all about timing… Darwin formulated his idea of natural selection in the early 1840s. He did not publish them until 1858. Conflict! Alfred Wallace
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What Data did Darwin collect? (i.e., what is the evidence for evolution?) 1. Fossil Record 2. Biogeography 3. Comparative Embryology 4. Comparative Anatomy 5. Molecular Biology
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A Skull of Homo erectus B Ammonite castsC Dinosaur tracks Fossilized organic matter of a leaf E Insect in amber F “Ice Man” D 1. The Fossil Record
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Pelvis and hind limb Rhodocetus (predominantly aquatic) Pakicetus (terrestrial) Dorudon (fully aquatic) Balaena (recent whale ancestor) Pelvis and hind limb
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North America = Living lungfishes Australia Africa Asia Europe South America = Fossilized lungfishes 2. Biogeography
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Present Eurasia Millions of years ago 65.5 135 251 Mesozoic Cenozoic Paleozoic Madagascar India Australia Africa Antarctica South America North America Laurasia Gondwana Pangaea
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2. Biogeography All the species of finches on the Galapagos Islands look like finches native to the West Coast of South America—but not exactly the same “Adaptive Radiation”
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Pharyngeal pouches Post-anal tail Chick embryo Human embryo 3. Comparative Embryology
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Humerus Radius Ulna Carpals Metacarpals Phalanges HumanCatWhaleBat 4. Comparative Anatomy Homologous Structures = Divergent Evolution
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Pelvis and hind limb Dorudon (fully aquatic) Balaena (recent whale ancestor) Pelvis and hind limb 4. Comparative Anatomy Vestigial Structures: What are left of homologous structures
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Dorudon Balaena
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Modern-Day Humpback Whale
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Analogous Structures = Convergent Evolution Homologous Analogous
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5. Molecular Biology http://www.geneticorigins.org/mito/media2.html http://evolution.berkeley.edu/evosite/evo101/IIE1cMolecularclocks.sht ml Comparison of DNA sequences from different organisms is very helpful in determining relationships. Molecular analysis is best done together with other types of analyses.
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