Descent With Modification: A Darwinian View of Life

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

2. What Evolution Is • Descent with modification • Change in genetic frequencies over time • Change with inheritance From http://evolution.berkeley.edu/evosite/evo101/IIntro.shtml

3. What Evolution Isn’t • It is not a theory that says humans came from apes!

4. Historical Context of Evolution People have always wondered about the origin of diverse life forms on Earth.

5. Aristotle and Scala Naturae • Aristotle believed that there was a Divine Creator at the top of a ladder, and everything else descended from that being. From http://www.ivirgil.it/set/Darwin/creazionismo.htm

6. Carolus Linnaeus • Created a system of taxonomy that did not show relationships between organisms.

7. Georges Cuvier • Observed changes in fossil layers of rock • Surmised that layers were different due to catastrophes (floods, ice ages)

8. Lamarckian View of Evolution

9. What Lamarck Observed • More modern fossils were found in upper layers of rock • This led to the formation of more modern species

10. Use and Disuse • Body parts used to get along in the environment get stronger and larger • Those that aren’t used, deteriorate.

11. Inheritance of Acquired Characteristics • Modifications acquired during an organism’s lifetime could be passed on to their offspring.

12. Dispelling the myths • Neither of these things were possible because they were missing a very important component…

13. Darwinian View of Evolution

14. Darwin backgrounder • Grew up very wealthy, educated • Was a med student, then a divinity student • Served as a naturalist for British government on the HMS Beagle

15. Where Darwin Went

16. Development of Theory of Natural Selection • Darwin observed 12 species of finches • Noted differences in beaks and how that correlated to food choice

17. What Darwin noticed • Organisms on the South American continent looked like those on the Galapagos but didn’t live anywhere else • Was influenced by Lyell (Principia Geologica)

18. Descent with Modification • Supposed that all organisms were related to an ancient ancestor

19. Natural Selection After studying specimens he collected, analyzing data and reading an essay by Thomas Malthus, Darwin formulated a theory that explained how different species originated.

20. Tenet #1 • Variation exists among members of a species.

21. Tenet #2 • This variation is inherited.

22. Tenet #3 • There are limited resources in the environment. There is a struggle for survival.

23. Tenet #4 • Organisms with favorable traits are more fit, thus they leave behind more offspring than those who are less fit.

24. Tenet #5 • These favorable traits persist in the population and will become more frequent.

25. Result: • Differential reproductive success leads to change in favorable traits among generations

26. In sum… • Natural selection occurs as a result of interactions between the environment and the genetic variability demonstrated in living organisms. • It is the result of differential reproductive success.

27. Artificial Selection • Organisms with certain traits are bred repeatedly until population has only that trait • Dog breeds are another good example

28. Other Evidence for Evolution • There is other evidence that evolution has occurred: • Anatomical • Molecular • Fossil Record • Biogeography Fossil of Archaeopteryx, ancient bird

29. Homologous Structures

30. Vestigial Structures • Structures which are smaller or reduced in size because they are no longer used/needed • Whale pelvis • Vestigial legs on snakes • Human appendix

31. Embryological Similarities • Presence of post-anal tail, pharyngeal gill slits indicates common ancestry • What else does it indicate?

32. Molecular homologies • Amino acid sequences among vertebrates have similarities • What else is similar?

33. Fossil Record • Transitional forms show the change from simpler forms to more complex forms

34. Biogeography • Geographic distribution of species • Similar species live in the same area