1. Modern Evolutionary Theory I. Post-Darwinian Facts II. Population Genetics III. Post-Darwinian Theory

2. A. Mutationist School (1900-1930) Richard GoldschmidtT. H. Morgan large mutations are the major agent of evolutionary change

3. III. Post-Darwinian Theory A. Mutationist School (1900-1930) B. The Modern Synthesis (1940)

4. Post Darwinian Developments I. Genetics C. Population Genetics 1. 1908-10: Hardy - Weinberg - (Castle)

5. Post Darwinian Developments I. Genetics C. Population Genetics 1. 1908-10: Hardy - Weinberg - (Castle) after one generation of random mating, and equilibrium is reached in genotypic frequencies.

6. Post Darwinian Developments I. Genetics C. Population Genetics 1. 1908-10: Hardy - Weinberg - (Castle) 2. 1912-1988: Sewall Wright

7. Post Darwinian Developments I. Genetics C. Population Genetics 1. 1908-10: Hardy - Weinberg - (Castle) 2. 1912-1988: Sewall Wright - plant and animal breeding - statistical modelling of evolution - Drift - 'Wright' Effect

8. Post Darwinian Developments I. Genetics C. Population Genetics 1. 1908-10: Hardy - Weinberg - (Castle) 2. 1912-1988: Sewall Wright 3. 1930 - R. A. Fisher - statistician - ANOVA - The Genetical Theory of Natural Selection

9. Post Darwinian Developments I. Genetics C. Population Genetics 1. 1908-10: Hardy - Weinberg - (Castle) 2. 1912-1988: Sewall Wright 3. 1930 - R. A. Fisher 4. 1932 - J. B. S. Haldane - The Causes of Evolution - Stressed the importance of selection over mutation

10. Post Darwinian Developments I. Genetics C. Population Genetics 1. 1908-10: Hardy - Weinberg - (Castle) 2. 1912-1988: Sewall Wright 3. 1930 - R. A. Fisher 4. 1932 - J. B. S. Haldane 5. 1937 - T. Dobzhansky - pop gen of D. psuedoobscura inversions - Genetics and the Origin of Species - 'isolating mechanisms'

11. Post Darwinian Developments I. Genetics C. Population Genetics 1. 1908-10: Hardy - Weinberg - (Castle) 2. 1912-1988: Sewall Wright 3. 1930 - R. A. Fisher 4. 1932 - J. B. S. Haldane 5. 1937 - T. Dobzhansky 6. 1942 - Ernst Mayr - naturalist, not geneticist - influenced Dobzhansky's interpretations - Systematics and the Origin of Species - biological species concept

12. Post Darwinian Developments I. Genetics C. Population Genetics 1. 1908-10: Hardy - Weinberg - (Castle) 2. 1912-1988: Sewall Wright 3. 1930 - R. A. Fisher 4. 1932 - J. B. S. Haldane 5. 1937 - T. Dobzhansky 6. 1942 - Ernst Mayr 7. 1942 - 1950: Huxley, Stebbins, Simpson

13. Post Darwinian Developments I. Genetics C. Population Genetics D. 1940's: The Modern Synthetic Theory of Evolution Sources of VariationAgents of Change MutationN.S.**** RecombinationDrift**** - crossing overMigration - independent assortmentMutation Non-random Mating VARIATION look familiar?

14. III. Post-Darwinian Theory A. Mutationist School (1900-1930) B. The Modern Synthesis (1940) C. Mayr's Contributions

15. III. Post-Darwinian Theory A. Mutationist School (1900-1930) B. The Modern Synthesis (1940) C. Mayr's contributions 1. The Biological Species Concept a. Mayr - Biological species concept - defined species as "groups of potentially reproducing organisms separated from other such groups".

16. III. Post-Darwinian Theory A. Mutationist School (1900-1930) B. The Modern Synthesis (1940) C. Mayr's contributions 1. The Biological Species Concept 2. Peripatric Speciation Evolutionary change should be most dramatic when the two most powerful agents (drift and selection) are at work: - when small groups of colonists settle a new habitat

17. III. Post-Darwinian Theory A. Mutationist School (1900-1930) B. The Modern Synthesis (1940) C. Mayr's contributions D. Eldridge and Gould - 1972 - Punctuated Equilibrium

18. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 1. Consider a large, well-adapted population

19. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 1. Consider a large, well-adapted population Effects of Selection and Drift are small - (it's already "well adapted" and it is large....) little change over time

20. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 2. There are always small sub-populations "budding off" along the periphery of a species range...(Peripatric speciation...)

21. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 2. Most will go extinct, but some may survive... X X X

22. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 2. These surviving populations will initially be small, and in a new environment...so the effects of Selection and Drift should be strong... X X X

23. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 3. These populations will change rapidly in response... X X X

24. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 3. These populations will change rapidly in response... and as they adapt (in response to selection), their populations should increase in size (because of increasing reproductive success, by definition). X X X

25. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 3. As population increases in size, effects of drift decline... and as a population becomes better adapted, the effects of selection decline... so the rate of evolutionary change declines... X X X

26. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 4. And we have large, well-adapted populations that will remain static as long as the environment is stable... X X X

27. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 5. Since small, short-lived populations are less likely to leave a fossil, the fossil record can appear 'discontinuous' or 'imperfect' X X X

28. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 5. Large pop's may leave a fossil.... X X X

29. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 5. Small, short-lived populations probably won't... X X X

30. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 6. So, the discontinuity in the fossil record is an expected result of our modern understanding of how evolution and speciation occur... X X X

31. - 1972 - Eldridge and Gould - Punctuated Equilibrium TIME VARIATION 6. both in time (as we see), and in SPACE (as changing populations are probably NOT in same place as ancestral species). X X X

32. Modern Evolutionary Theory I. Post-Darwinian Facts II. Population Genetics III. Post-Darwinian Theory A. Mutationist School (1900-1930) B. The Modern Synthesis (1940) C. Mayr's Contributions D. Punctuated Equilibrium (1972 - Eldridge and Gould) So, our modern evolutionary theory PREDICTS that transitional fossils should be rare, because most evolutionary change is occurring in small, isolated populations in new environments. This solves Darwin's remaining dilemma regarding the 'incompleteness' of the fossil record, and explains why we don't have intermediates for every possible lineage.