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Chapter 3

Chapter 3. Postulates of Natural Selection. Two important terms. Fitness Survival and reproduction Adaptation A relative increase in fitness. Natural Selection. What it is and What is NOT. Q1. Evolution deals with changes in genotypes but Natural selection acts on phenotypes. True

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Chapter 3

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  1. Chapter 3

  2. Postulates of Natural Selection

  3. Two important terms Fitness Survival and reproduction Adaptation A relative increase in fitness

  4. Natural Selection What it is and What is NOT

  5. Q1. Evolution deals with changes in genotypes but Natural selection acts on phenotypes. • True • False

  6. Q2. Selection acts on populations of organisms • True • False

  7. 1. Selection acts on individuals but its consequences occur in populations

  8. 2. Natural selection acts on phenotypes but Evolution consists of changes in allele frequencies (genotypes).

  9. 3. Natural Selection is NOT forward looking

  10. 4. New Traits can evolve, even though natural selection acts only on existing traits in the current generation.

  11. Q3. The ultimate result of Natural selection is to perfectly fit an organism for its environment. • True • False

  12. 5. Natural Selection does not lead to perfection

  13. 6. Natural Selection is Nonrandom, but it is not progressive. • Increase in complexity, organization or specialization may occur • No specific end goal in mind, however • There is no trend toward more advanced forms, could just as easily go in reverse (oscillating selection).

  14. 7. Fitness is NOT circular • The following claim is often made: • “Of course individuals with favorable variations are the ones that survive and reproduce because the theory defines favorable as the ability to survive and reproduce.” • What is wrong with this argument?

  15. Q4 Selection acts for the good of the species and does not work on lone individuals. • True • False

  16. 8. Selection acts on individuals and not for the good of the species.

  17. Difficulties that Darwin dealt with • Where does variation come from? • How are traits inherited from parents?

  18. Evolutionary Synthesis Mayr article discussion

  19. Q5. After viewing the following list of traits choose the group they belong to. • Studied biodiversity and origin of new taxa • Macroevlolution • Properties in individuals are objects of selection • Speciation is a gradual accumulation of changes • Geneticists • Naturalists

  20. 1. What were the two widely divergent fields in evolutionary biology in the early 1900’s?

  21. Genetics • Based on small changes within populations • Microevolution • Gene is the object of selection • Mutations lead to saltational speciation • Naturalists • Studied biodiversity and origin of new taxa • Macroevlolution • Properties in individuals are objects of selection • Speciation is a gradual accumulation of changes

  22. 2. What parts of Darwin's theory were hardest for scientists to accept?

  23. First what was well accepted? • Change in organisms occurs over time • The branching theory implying common descent • What had difficulty being accepted? • That evolution was a gradual process • That species multiplied (increase in diversity) • That natural selection was the means

  24. 3. Why was the synthesis of geneticists and naturalists delayed?

  25. Scientists worked in isolation in different countries. Beliefs in each country were dictated by the most powerful scientists. • Scientists in different branches of biology had different prevailing ideas • Each group thought that the other group had no flexibility in their beliefs.

  26. 4. What were the major ideas in each group’s thinking?

  27. Geneticists • Worked in labs and studied the processes in single populations • Only examined changes within a population-microevolution • Believed each mutation led to a new species • Believed speciation was saltational • Gene is the object of selection

  28. Hugo DeVries • Developed mutation theory • Any new variation caused by mutation was actually a new species • Emphasized random genetic variation (no guidance by selection) • Speciation abrupt and spontaneous

  29. Naturalists • Studied biodiversity and the origin of new species and higher taxa - macroevolution • Changes occur gradually as Darwin said • Individual is object of selection not the gene • New species are formed by geographic isolation

  30. Q6 Was Ernst Mayr a naturalist or a geneticist? • Naturalist • Geneticist

  31. 5. Who were the major proponents of each school?

  32. Geneticists also called mutationists • William Bateson and HugoDeVries • Other geneticists who also believed evolution was gradual were not as well known to naturalists. • Edward East and Sergei Chetverikov.

  33. Naturalists • Moritz Wagner • Karl Jordan • Edward Poulton • Sergei Chetverikov • Erwin Stresemann • Ernst Mayr and • Julian Huxley

  34. Problem – how can the changes in the genes of an individual result in the selection for a trait in a population?

  35. Q7. According to Ernst Mayr, who brought the two sides together • Thomas Hunt Morgan • Theodosius Dobzhansky • Ledyard Stebbins • Ernst Mayr • R. A. Fisher

  36. 6. Who brought the two sides together?

  37. Thomas Hunt Morgan – his research was a key factor in the synthesis • He showed (working with Drosophila) that • mutations occurred in every generation and • that the resulting populations were reproductively isolated and were not new species. • Mutations simply increased the variability of a population. • Theodosius Dobzhansky – was a naturalist in Russia, came to US and worked in Morgan’s lab • He saw how they were complimentary to each other. • Mutations provide the new alleles that increases variation in populations. • Geographically separated populations can then respond to different environments • gradually, become separate species. • Over more time new higher taxa can emerge.

  38. 7. What is the actual object of selection?

  39. Selection acts on individuals but has its effects in populations.

  40. 8. How well has the Darwinian theory withstood the test of time?

  41. Some major players since the synthesis? • Population genetics and microevolution. • R.A. Fisher – mathematician showed variability in populations could be explained using Mendel’s laws • Genetical Theory of Natural Selection • Believed selection was favored in large populations because variability remains high due to mutation and genetic recombination • Selection acts uniformly and slowly • J.B.S. Haldane • Same basic understanding as Fisher but he emphasized the use of practical examples for his models ( e.g industrial melanism and moths) Sewall Wright • Mathematical techniques to show that evolution could proceed in isolated groups • Developed the ideas of genetic drift. (based on the work of William Castle)

  42. Others cont. • John Maynard Smith • Extended the Darwinian theory to explanation of animal behavior • Ledyard Stebbins – • did for plant evolution what Dobzhansky with his fruit flies had done for animal evolution • George Gaylord Simpson • Reinterpreted the fossil record • Major responsibility for paleontologists embracing Darwin's ideas.

  43. EVIDENCE OF CHANGE THROUGH TIME

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