Evolution Theories: Lamarck's Theory and Darwin's Theories

1. Evolution Theories and Evidence

2. Evolution • An orderly succession of changes. • Biological evolution is the change of populations of organisms over generations. • Came from a common ancestor

3. One of the first to propose a hypothesis of species modification. Lamarck’s Theory

4. Lamarck’s Theory • Proposed that species evolve over time. • Similar species descended from a common ancestor.

5. Lamarck’s Theory (cont’d) • Incorrectly hypothesized that species modification is the result of acquired traits and that these traits can be passed on to offspring. • Acquired traits: one not determined by genes, but arises during an organism’s lifetime as a result of the organism’s experience or behavior.

6. Lamarck’s Theory (cont’d) • Example: • Lamarck’s theory said that webbed feet of water birds resulted from repeated stretching of the membrane between the toes.

7. Lamarck’s Theory (cont’d) • Over time, this produced a broad webbed foot, at trait that would be preserved by reproduction (offspring of parents with webbed feet would have webbed feet as well).

8. Lamarck’s Theory (cont’d) • Another example: giraffes

9. Lamarck’s Theory (cont’d) • Lamarck’s hypothesis was widely attacked and was easily disproved.

10. Began his work on evolution when employed as a naturalist for a voyage of the H.M.S. Beagle. Darwin’s Theories50 years later (1809-1882)

11. Darwin’s Theories

12. Darwin’s Theories • Found evidence of species modification in both modern and extinct species.

13. Darwin’s Theories (cont’d) • His ideas about evolution and natural selection are summed up in two theories: • Descent with Modification • Modification by Natural Selection

14. Darwin’s Theories (cont’d) • Descent with Modification • Newer forms appearing in the fossil record are actually the modified descendents of older species. • Example: Galapagos finches (13 Species) • Each had a distinct bill for eating.

16. Darwin’s Theories (cont’d) • All species had descended from one or a few original types of life. • This explained the observation that organisms give rise to others similar to themselves. • “Origin of Species”

17. Darwin’s Theories (cont’d) • Modification by Natural Selection • Natural selection is the principal driving force behind evolution. • Environment may affect individual organisms in a population in different ways, because individuals of a species are not identical.

18. Darwin’s Theories (cont’d) • Some organisms have traits that make them better able to cope with their environment. • Organisms with a great number of favorable traits tend to leave more offspring than organisms with fewer beneficial traits. • Different degrees of successful reproduction: natural selection.

19. Darwin’s Theories (cont’d) • If a trait both increases the reproductive success of an organism and is inherited, then the trait will tend to be passed on to many offspring. • A population of organisms adapt to their environment as their proportion of genes for a favorable trait increases.

20. Darwin’s Theories (cont’d) • Resulting change in the genetic makeup of a population is evolution. • A single organism’s contribution to the next generation is termed fitness. • A favorable trait gives an organism that has it an adaptive advantage.

21. Darwin’s Theories (cont’d) • The environment “selects” the traits that will increase in a population. • Example: Peppered Moths

22. Peppered Moths

23. Darwin’s Theories (cont’d) • Selection conditions change as the demands of the environment change. • If change is too fast, populations may not adapt fast enough and will become extinct.

24. Evidence of Evolution • Evidence supporting evolution is found in the body structures of living organisms.

25. Evidence of Evolution (cont’d) • Homologous features: similar features that originated in a shared common ancestor.

26. Evidence of Evolution (cont’d) • Example: forelimbs in human, bat, penguin, and alligator • Look different • Vary in function • Very similar in skeletal structure • Derived from the same embryological structures

27. Forelimbs of Vertebrates

28. Evidence of Evolution (cont’d) • Analogous features: serve identical functions and look somewhat alike. • Very different embryological development • May be different in internal anatomy.

29. Evidence of Evolution (cont’d) • Example: wings in birds and insects. • Share a very remote ancestor • Wings evolved independently and differently in more recent ancestors.

31. Evidence of Evolution (cont’d) • Vestigial features: serve no useful function. • Examples: human appendix and tailbone • Were useful to an ancestor, but no longer usefulto modern organisms.

32. Evidence of Evolution (cont’d) • Evidence that the feature was functional in some ancestors of the modern organism. • Modern organism with such feature, probably shares common ancestry with an organism that has a functional version of that feature.

33. Evidence of Evolution (cont’d) • Similarities in Embryology • Similar embryological development among species indicates a common evolutionary history.

34. Early stages of different vertebrate embryos are very similar. Evidence of Evolution (cont’d)

35. Evidence of Evolution (cont’d) • Similarities in Macromolecules: • Similarity in DNA, RNA, and proteins indicates a common evolutionary history. • The more similar the macromolecules, the more closely related the species are thought to be.

36. Patterns of Evolution • Coevolution: two or more closely associated species change in response to each other. • Example: plants and their pollinators

37. Patterns of Evolution (cont’d) • Convergent Evolution: organisms that are not closely relatedresemble each other because they have responded to similar environments.

38. Example: sharks and porpoises appear very similar, but are not closely related. Environment selects similar phenotypes. Analogous features associated with convergent evolution. Patterns of Evolution (cont’d)

39. Patterns of Evolution (cont’d) • Divergent Evolution: related populations become less similar as they respond to different environments. • Can ultimately result in a new species.

40. Adaptive radiation:many related species evolve from a single ancestral species. Example: Galapagos finches Patterns of Evolution (cont’d)

41. Patterns of Evolution (cont’d) • Process can be sped up artificially through artificial selection. • Example: dog breeding.