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Transcript
Darwin’s Theory of Evolution 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’) Pre-Darwin • Lamarck (early 1800s) • Buffon • Inheritance of Acquired Characteristics 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” Who was Darwin? • Surgeon in training • Minister • Recruited by captain of HMS Beagle • Set sail in 1831 at the age of 22 Not just the Galapagos… Not just finches… 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. 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) • Darwin called these conclusions “Descent with Modification” • We call it “Natural Selection” Important!! • What is ‘favorable’ in one environment may not be in another environment. • The environment determines what is favorable and unfavorable. 4 Take-home Points about Natural Selection • 1. Individuals DO NOT evolve. Evolution refers to generation-togeneration changes in a population. • 2. Natural selection can only amplify or diminish traits that are inheritable. 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. 4 Take-home Points about Natural Selection • 4. Evolution is about compromise. It’s all about timing… • Darwin formulated his idea of natural selection in the early 1840s. • He did not publish them until 1858. Alfred Wallace What Data did Darwin collect? (i.e., what is the evidence for evolution?) • • • • • 1. 2. 3. 4. 5. Fossil Record Biogeography Comparative Embryology Comparative Anatomy Molecular Biology 1. The Fossil Record B Ammonite casts A Skull of Homo erectus D Fossilized organic matter of a leaf C Dinosaur tracks E Insect in amber F “Ice Man” Pakicetus (terrestrial) Rhodocetus (predominantly aquatic) Pelvis and Dorudon (fully aquatic) hind limb Pelvis and hind limb Balaena (recent whale ancestor) 2. Biogeography North America Asia Europe Africa South America Australia = Living lungfishes = Fossilized lungfishes Cenozoic Present Eurasia Africa India South America Madagascar 65.5 135 251 Mesozoic Laurasia Paleozoic Millions of years ago Antarctica 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” 3. Comparative Embryology Pharyngeal pouches Post-anal tail Chick embryo Human embryo 4. Comparative Anatomy Homologous Structures = Divergent Evolution Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat 4. Comparative Anatomy Pelvis and hind limb Dorudon (fully aquatic) Pelvis and hind limb Balaena (recent whale ancestor) Vestigial Structures: What are left of homologous structures Dorudon Balaena Modern-Day Humpback Whale Homologous Analogous Structures = Convergent Evolution Analogous 5. Molecular Biology Comparison of DNA sequences from different organisms is very helpful in determining relationships. Molecular analysis is best done together with other types of analyses. http://evolution.berkeley.edu/evosite/evo101/IIE1cMolecularclocks.sht ml http://www.geneticorigins.org/mito/media2.html