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Evolutionary Theories: From Darwin to Modern Synthesis

Explore the evolution of evolutionary theories from Darwin's time to the Modern Synthesis era, including key developments in population genetics and post-Darwinian advancements by influential figures like Goldschmidt, Haldane, Dobzhansky, Mayr, and Eldridge. Delve into the Mutationist School, the Modern Synthesis period, Mayr's contributions, and Eldridge and Gould's Punctuated Equilibrium theory. Understand the genetic underpinnings, selection forces, species concepts, and speciation processes that shape evolutionary change in populations. Discover how mutation, selection, drift, and other factors interact to drive the diversity of life on Earth.

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Evolutionary Theories: From Darwin to Modern Synthesis

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

  2. III. Post-Darwinian Theory A. Mutationist School (1900-1930) Richard Goldschmidt T. 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 Variation Agents of Change Mutation N.S.**** Recombination Drift**** - crossing over Migration - independent assortment Mutation 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 1. Consider a large, well-adapted population VARIATION TIME

  19. - 1972 - Eldridge and Gould - Punctuated Equilibrium 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 VARIATION TIME

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

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

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

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

  24. - 1972 - Eldridge and Gould - Punctuated Equilibrium 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 VARIATION X X TIME

  25. - 1972 - Eldridge and Gould - Punctuated Equilibrium 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 VARIATION X X TIME

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

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

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

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

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

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

  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.

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