1. Chapter 22 Descent with Modification: A Darwinian View of Life

2. Question? u How did the diversity of life originate? u Through the process of Evolution.

3. Evolution u The processes that have transformed life on earth from its beginnings to today's diversity. u “Nothing in Biology Makes Sense Except in the Light of Evolution”- Theodosius Dobzhansky

4. u Note: Evolution does NOT say anything about how life originated u It DOES describe how life changes through time.

5. Early Ideas on Life’s Diversity 1. Plato - Organisms are already perfectly adapted to their environments. 2. Aristotle - Organisms arranged on a “scale of life” from simple to complex.

6. Result u No evolution. u Life is already perfect and doesn’t need to change. All the rungs on life's "ladder" are already occupied.

7. Carolus Linnaeus u (1707-1778) u Classified life according to genus and species. u Thought the diversity in life was fixed from life’s origins u Each lifeform was perfectly designed from the beginning for its role u Still use his classification system today

8. Catastrophism u Georges Cuvier (1769-1832). u Attempted to relate fossils to current life.

9. Theory u Fossils were the remains of species lost due to catastrophe. u No new species originated; species could only be lost over time. u Result - No evolution.

10. James Hutton u 1795 - Gradualism u Profound change is the cumulative product of slow, but continuous processes.

11. Result u Changes on the earth were gradual, not catastrophic.

12. Charles Lyell u 1797 - 1875. u Incorporated Hutton’s gradualism into a theory called Uniformitarianism.

13. Uniformitarianism u Geological processes have operated at the same rate over the Earth’s history.

14. The lower the stratum, the more dissimilar life is to today’s life

15. Result u The Earth must be VERY old. (much older than 6000 years of the fixed species concept). u Idea that slow and subtle processes can cause substantial change.

16. Jean Baptiste Lamarck u Published theory in 1809. u Theory - Life changed from simple to complex over time.

17. Lamark u Fossils were the remains of past life forms. u Evolution did occur. u First to propose a mechanism for evolution

18. Mechanisms 1. Use and Disuse - u Body parts used to survive become larger and stronger. u Body parts not used to survive deteriorate.

19. Mechanisms 2. Acquired Characteristics u Modifications acquired by use/disuse were passed on to offspring.

21. Problem u No knowledge of genetics. u Acquired traits are not transmitted offspring.

22. Lamarck’s Credits u Did suggest correctly the role of fossils in evolution. u Did suggest that adaptation to the environment is a primary product of evolution.

23. Thomas Malthus u Essay on human population growth in 1798. u Disease, famine, homelessness, and war are inescapable because human populations grow faster than food supplies. u Darwin read Malthus.

24. Charles Darwin u Father of the modern theory of evolution. u Theory - Descent with Modification.

25. Darwin's Background u Trained as a Naturalist (after trying religion and medicine).

26. Voyage of the Beagle

27. Result u Darwin's training and travel opportunities allowed him to formulate and support his ideas on Natural Selection. u On twitter: @cdarwin

29. Darwin - 1859 u Publication of "The Origin of Species”

30. Comment u Darwin best remembered for the theory because of his overwhelming evidence and because he published.

31. Darwinian View u History of life is like a tree with branches over time from a common source. u Current diversity of life is caused by the forks from common ancestors.

33. Example

34. “The Origin of Species” u Documented the occurrence of evolution. u Suggested that the mechanism for evolution was Natural Selection.

35. Observations: Observation 1 – Members of a population often vary greatly in their traits..

36. Observation 2 u Traits are inherited from parents to offspring.

37. Observation 3 All species are capable of producing more offspring than their environment can support.

38. Observation 4 u Owing to lack of food or other resources, many of these offspring do not survive.

39. Inference 1 u Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals.

40. Inference 2 u This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

41. Nature u Determines which characteristics are favorable. u Determines who survives. u Result - “Natural Selection”

42. Natural Selection in action

43. Artificial Selection u When man determines the characteristics that survive and reproduce. u Result - the various breeds of animals and plants we’ve developed. u https://www.youtube.com/watch ?v=0jFGNQScRNY https://www.youtube.com/watch ?v=0jFGNQScRNY

45. Evolution Success Measured By u Survival u Reproduction u Whoever lives long enough and has kids is the “winner” in evolution.

46. Subtleties of Evolution 1. Populations are the units of Evolution. 2. Only inherited characteristics can evolve.

47. Comment u Acquired characteristics may allow a species to evolve "outside" of Natural Selection. u Ex: culture, learning

48. Evidences for Evolution u Direct observation of evolutionary changes. u Fossils u Homology u Convergent Evolution u Biogeography u Molecular

49. Direct Observations u Drug resistant HIV u Beak size in Birds u Many Others

50. HIV Drug Resistance u Drug resistance strains selected for by treatments u Result – resistant strains became 100% dominant in 4-5 weeks.

52. Beak Size u Field Study – measured the beak size of all birds in a population over several years. u Result – drought and food competition changed beak size.

54. Fossils u Relics or impressions of organisms from the past. u Problem: u Show changes over time from simple to complex. u Many fossils don't have descendants.

55. Evolution Viewpoint u Life has changed over time. u Many species failed to survive and became extinct.

56. Comments 1. Fossilization is a rare event. 2. Only hard parts fossilize well. 3. Problem in finding fossils. 4. Interpretation. 5. Missing Links.

57. Homology Homology- similarities resulting from common ancestors Mammal forelimbs

58. Homology in Embryos u Problem - closely related organisms go through similar stages in their embryonic development. u Ex: Gill pouches in vertebrates

60. Evolution Viewpoint u Ontogeny is a replay of Phylogeny. (Development reflects descent) u Development reflects inheritance of common control genes.

61. Problems Vestigial Organs - Rudimentary structures of marginal, if any, use. Whale Legs

62. Human Example

63. Evolution Viewpoint u Remodeling of ancestral structures as their functions or adaptations changed.

64. Convergent Evolution u Unrelated organisms show similar adaptations. u Cause – lived in a similar environment with similar selection pressures.

65. Analogous Structures-similar function, but the structures are NOT from a common ancestor

66. Biogeography u The geographical distribution of species. u Problem: u Species mixtures on islands u Marsupials in Australia

67. Evolution Viewpoint u Biogeographical patterns reflect descent from the ancestors that colonized that area.

69. Molecular Biology u Study of Evolution at the DNA or protein levels. u Related species have similar DNA sequences.

71. Evolution Viewpoint u Related species share a common ancestrial DNA. The closer the relationship, the more similar the DNA sequences should be.

72. Summary u Darwin's ideas now a "Theory”. u Predictions of a Theory are tested by experiments and observations. u Be familiar with the pre-Darwin views of evolution.

73. Summary u Know Darwin’s “observations” and “inferences”. u Be able to discuss the various evidences of Darwinian evolution.