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Evolution by Natural Selection

Evolution by Natural Selection. How did life originate? Why are all the species we see on earth in existence? 3 main ideas. Creationism. Seeding theory. Evolution by natural selection.

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Evolution by Natural Selection

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  1. Evolution by Natural Selection

  2. How did life originate? Why are all the species we see on earth in existence? 3 main ideas

  3. Creationism

  4. Seeding theory

  5. Evolution by natural selection

  6. In the distant future . . . Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. --Charles Darwin, 1859

  7. Landmarks in the History of Evolutionary Thinking

  8. Evolution Before Darwin • Change over time in organic structures (evolution) • Characteristics seemed to have a purpose (porcupines, turtles, skunks)

  9. Jean Pierre Antoine de Monet de Lamarck (1744-1829) Two causes of species change: 1. Progress toward a higher form 2. Inheritance of acquired characteristics

  10. Darwin’s Theory of Natural Selection • The explanatory challenge: 1. why change takes place 2. how new species emerge 3. what the functions are of parts

  11. One clue: Malthus: more organisms produced than survive and reproduce,leading to “a struggle for existence”

  12. More individuals produced than can possibly survive

  13. Struggle for Survival

  14. Natural Selection • Variation • Inheritance • Differential Reproduction

  15. The key to natural selection: Differential reproductive success because of heritable variants; everyone has ancestors, but not everyone leaves descendants

  16. Natural selection provided 3 key answers • Explained change over time (descent with modification) • Explained apparent purposive quality of component parts • United all species into one grand tree of descent (including humans)

  17. Problems That Troubled Darwin 1. Phenomena that seemed inexplicable on the theory of “survival selection” 2. The existence of sex differences.

  18. Objections to Natural Selection • No theory of inheritance at the time • Hard to imagine utility of intermediate stages, and natural selection requires each step to benefit • Beliefs at the time that species were unchanging

  19. Three Products of Evolutionary Processes • 1. Adaptations • 2. Byproducts • 3. Noise

  20. Adaptations • 1. inherited characteristics • 2. reliably developing in most or all species members • 3. produced by natural or sexual selection… • 4. because they solved an adaptive problem—functionality • 5. must have contributed to reproductive success, directly or indirectly • 6. need not be present at birth (teeth, breasts, beards, desires, etc.)

  21. One Example of Adaptation: Umbilical Cord

  22. Byproducts • Characteristics that do not solve adaptive problems • Do not have functional design • Are “carried along” with characteristics that do have functional design

  23. Examples of Byproducts: belly button

  24. More Examples of Byproducts • belly button • heat from light bulb • white color of bones • Attributing intentionality to objects that do not have intentionality (sun, clouds)

  25. Noise: random effects due to mutations or perturbations during developmentExamples: shape of belly button;perturbation in roundness of glass bulb

  26. Adaptations are the primary products of natural and sexual selection

  27. Sexual Selection • Intrasexual Competition • Intersexual Selection

  28. “The sight of the peacock gives me nightmares” – Charles Darwin

  29. Intrasexual Competition • competition among members of the same sex for mating

  30. Thought experiment: Examples in humans of intrasexual competition?

  31. Intersexual Selection:Preferential Mate Choice a form of sexual selection in which members of one sex are differentially attracted to members of the opposite sex

  32. Intersexual Selection:Preferential Mate Choice

  33. Two Kinds Of Causal Questions • Proximate: HOW a mechanism develops and operates • Ultimate: WHY a mechanism evolved—evolutionary forces that led to the creation of the mechanism; the adaptive problem it evolved to solve.

  34. Causal Question Why are men taller than women on average?

  35. Proximate and Ultimate Answers to Questions • Why are men taller than women on average? • Why do people grow calluses? • Why do people like to eat pizza? • Why do people get jealous?

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