Topics

2. Topics • The historical context of evolutionary theory • Darwin’s five theories of evolution • Evidence for evolution • Mechanisms of evolutionary change • Origins of diversity

3. The historical context of evolutionary theory • with the Copernican Revolution practitioners of science (Western) began to seek explanations for phenomena in the world • common view at this time was of a world that was constant and of short duration (based on calculations from the bible) • 17th and 18th century discoveries in geology (including fossils) seemed to indicate the great age of the earth • perhaps the earth was not so constant….

4. The historical context of evolutionary theory • Cuvier – catastrophism – earth was constant except for periodic massive changes • Jean-Baptiste de Lemarck – developed full-fledged evolutionary theory • Lyell – uniformitarianism – geological features are the result of natural laws slowly and constantly shaping the surface of the earth over vast stretches of time • Darwin – Can natural laws operating constantly over a log period of time explain the diversity of life on earth as well?

5. Who was Darwin • Born in 1809 son of a physician • interested in nature from a young age • studied medicine, but gave it up • Obtained a degree in theology at Cambridge • Joined a survey voyage of South America aboard the HMS Beagle as a naturalist – mostly as a companion for Captain Fitzroy

6. Questions that Darwin asked • Why is island fauna so different from mainland? • How do species originate? • Why are fossils of Patagonia so similar to extant species? • Why does each island in a chain seem to have similar but unique species?

7. Darwin’s five theories • Nonconstancy of species (Evolution) • Common descent • Gradualness of evolution • Multiplication of species by branching • Natural selection

8. Evidence – fossil record geological sediments occur in strata (layers) older layers are under newer layers fossils found in newer layers are more similar to extant species “missing links” and transitional forms are common – especially given the low probability of fossilization

9. Evidence – taxonomy • Swedish botanist Carolus Linnaeus developed system of classification based on similarity of structures • Found species could generally be placed in a hierarchy (Linnaean hierarchy) • Kingdom-Phylum-Class-Order-Family-Genus-Species • Consistent with common descent and branching evolution

10. Evidence – Homology Similar structures, in the same relative position, same embryological origin, yet they serve different purposes

11. Evidence – Embryology FISH REPTILE BIRD (chicken) MAMMAL (human) indicates common early developmental pathways

12. Evidence – Vestigial structures cave crayfish are blind, but they have “eyes”

13. Evidence – Biogeography • Fauna of North America and Europe are very similar – why? • Continental drift • Camels are found in Asia and Africa, their close relatives, llamas in South America. How could this happen? • Tertiary period fossils of camels found in North America

14. Evidence – Molecular • Organisms that are more similar (putatively related) have more similar DNA and protein sequences • By comparing sequences we can infer an evolutionary tree of relatedness that often matches trees built on other data (e.g. morphology)

15. Evidence – Natural selection in the wild • Antibiotic resistance in bacteria • Drug resistance in HIV (evolution within an individual human) • Beaks of finches in Galapagos • Peter and Rosemary Grant have measured evolution of beaks and correlated changes with drought • Guppies in Trinidad • John Endler has shown that predators cause evolution of drab coloration among fishes, removing predators causes fish to become more colorful (sexual selection)

16. Mechanisms of Evolution • Natural selection • Sexual selection • Genetic drift • Mutation • Gene flow Doni Kendig

17. Apes Common ancestor Speciation What is wrong with this statement…If humans evolved from apes, why are there still apes around? Humans

18. Speciation What happens here?

19. Split into two species • But what is a species? • Biological species concept • Species are groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups • Doesn’t always work well – other concepts exist • What is your definition of a species?

20. Speciation • The key: barriers to gene flow • Why is this important? • Reproductive isolation evolves as a by-product of genetic changes that occur for other reasons

21. Mechanisms of divergence • Natural selection • Different environments • Genetic drift • Random chance – differences occur because populations are independent

22. Divergence allows emergence of reproductive isolating mechanisms • Premating isolating mechanisms • Mates do not meet • Potential mates are behaviorally incompatible • No transfer of sperm – mechanical incompatibility • Egg is not fertilized – gametic incompatibility

23. Divergence allows emergence of reproductive isolating mechanisms • Post-mating isolating mechanisms • Zygote dies • Reduced hybrid viability • Hybrid sterility

24. Mechanisms of Evolution • Consider a species of snails in the genus Conus, living on patch reefs in Hawaii. • Imagine that these snails are found on several different reefs with different degrees of isolation. • Draw pictures of the variation, within and among reefs from several islands (draw map). Explain why the differences arose (include as many mechanisms of evolution as you can).

25. http://www.pbs.org/wgbh/evolution/library/11/2/e_s_6.html http://www.pbs.org/wgbh/evolution/library/10/4/l_104_01.html

26. Systematics • Evolutionary systematics • concerned with identifying evolutionary relationships among species • identifying patterns of diversity over time • how is this different from taxonomy?

27. How can we determine these relationships? • fossil record • geological record • comparative embryology • homologous structures • comparative biochemistry

28. Species Phylogenies • Cladistic analysis (cladograms) • groups placed together based on shared-derived characteristics • species closer together on a tree share a more recent common ancestor

29. turtle cat gorilla human lungfish tail (loss) trout hair lamprey limbs lungs jaws conflicts often arise - why? Convergent evolution

30. Aloe Agave Convergent Evolution

32. Evolution of HIVfrom Papathanosopoulos et al. 2003 • UN program of HIV/AIDS • 2000 – 36 million infected • as of 2002, 65 million infected, 24 million dead • 95% of infections in developing countries • in sub-Saharan Africa, 29.4 million with HIV

33. National Institutes of Health HIV is a retrovirus – an RNA virus

34. HIV primarily attacks CD4+ T cells an important signaling cell in the immune system done by reverse transcriptase AZT works by interfering non-infectious virus requires processing of proteins by viral protease to mature protease inhibitors interfere here

35. Why is HIV so variable? • retrovirus (no proofreading) • high reproductive rate (1010 virions/day) • recombination

36. Exploiting the variability…

37. Evolution of HIVfrom Papathanosopoulos et al. 2003 • Where did HIV come from? • similar viruses • HIV-2 similar to SIVsm from sooty mangabey monkey • causes similar, slightly milder disease in West Africa • HIV-1 similar to SIVcpz from common chimpanzee • cause of worldwide pandemic

38. How did HIV make the leap to humans? Bushmeat hunting • leap to humans has probably happened several times for both major strains • HIV-1 contains three large groups that resulted from independent cross-species transmissions since early 1900’s