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Evolutionary Basics

Evolutionary Basics. What was the view of the world and nature before Darwin?. Static Universe The universe didn ’ t change through time. Problem - Fossil Evidence. What was the view of the world and nature before Darwin?. Static Universe 2. Earth Centred Universe.

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Evolutionary Basics

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  1. Evolutionary Basics

  2. What was the view of the world and nature before Darwin? Static Universe The universe didn’t change through time Problem - Fossil Evidence

  3. What was the view of the world and nature before Darwin? Static Universe 2. Earth Centred Universe Galileo - showed that this was wrong

  4. What was the view of the world and nature before Darwin? Static Universe Earth Centred Universe Great Chain of Being Problem - how do you incorporate new species?

  5. What was the view of the world and nature before Darwin? Static Universe Earth Centred Universe Great Chain of Being Argument from Design Each species was designed for a specific purpose Problem:

  6. How did this ‘traditional’ view (or Natural Theology) apply to Biology? Argument from Design The design of all organisms showed that there was an intelligent and benevolent Creator BUT…. How do disease organisms fit into this scheme ? Ebola

  7. How did this ‘traditional’ view (or Natural Theology) apply to Biology? Argument from Design The design of all organisms showed that there was an intelligent and benevolent Creator OR…. Why did some species go extinct?

  8. How did this ‘traditional’ view (or Natural Theology) apply to Biology? Argument from Design William Paley (1743 – 1805)

  9. How did this ‘traditional’ view (or Natural Theology) apply to Biology? Argument from Design Relationship between Species (Great Chain of Being) BUT .. vulnerable to extinction

  10. How did this ‘traditional’ view (or Natural Theology) apply to Biology? Argument from Design Relationship between Species Fixed Species and Relationships How do you incorporate new species?

  11. General Summary: The world/universe was designed by a benevolent Creator to function perfectly and its form and function were fixed through all time.

  12. But Evolution is about change What were the pre-Darwinian ideas of change through time?

  13. Pre-Darwinian Ideas of Organic Change 1. Georges Louis Leclerc, Comte de Buffon (1707-1788) Species - a distinct group maintained by reproduction Local Conditions Different species Ancestor Time

  14. Pre-Darwinian Ideas of Organic Change Georges Louis Leclerc, Comte de Buffon (1707-1788) Jean-Baptiste Lamarck (1744-1829)

  15. Pre-Darwinian Ideas of Organic Change Georges Louis Leclerc, Comte de Buffon (1707-1788) Jean-Baptiste Lamarck (1744-1829) Lamarck’s ideas: 1. Spontaneous generation

  16. Pre-Darwinian Ideas of Organic Change Georges Louis Leclerc, Comte de Buffon (1707-1788) Jean-Baptiste Lamarck (1744-1829) Lamarck’s ideas: Spontaneous generation Ascent up the scale of nature Different species Complexity of the organism Time

  17. Pre-Darwinian Ideas of Organic Change Georges Louis Leclerc, Comte de Buffon (1707-1788) Jean-Baptiste Lamarck (1744-1829) Lamarck’s ideas: Spontaneous generation Ascent up the scale of nature Acquired characteristics

  18. Originators of Modern Theories of Natural Selection Alfred Russell Wallace Charles Darwin

  19. Voyage of HMS Beagle

  20. Darwin’s Finches - Geospiza Galapagos tortoise - Geochelone

  21. Contributing Elements to Darwin’s theory 1. Charles Lyell (1797 - 1875) Gradualism (Uniformitarianism) All change through time can be explained by processes at work today No need to invoke catastrophic events

  22. Contributing Elements to Darwin’s theory Charles Lyell (1797 - 1875) Thomas Malthus (1766 - 1834) Populations of organism will grow faster than their food supply Population Number Food supply Time

  23. Contributing Elements to Darwin’s theory Charles Lyell (1797 - 1875) Thomas Malthus (1766 - 1834) Plant and Animal Breeders • showed that the form of a species could be changed over time

  24. Logic of Darwin’s Theory of Natural Selection (or Descent with Modification) Observation Deduction All organic populations can exponentially. In spite of Obs. 1, they don’t. There is some kind of struggle for existence. This differential reproduction/survival is natural selection All members of a species are not the same. Differences in individuals are passed to their offspring. 2. Some members of a species are better equipped to survive and reproduce than others.

  25. Journal of the Proceedings of the Linnean Society of London. Zoology 3 (20 Aug.): 45-62

  26. Definition of Evolution Changes over time of the proportion of individuals differing genetically in one or more traits These changes can occur by: • Changes in frequency of alleles and/or phenotypes in a population • Changes in the proportion of different populations in a species • Changes in the number of species in a larger taxonomic group Evolution is the pattern of change over time.

  27. Changes over time of the proportion of individuals differing genetically in one or more traits **PATTERN** Natural Selection Differential success in the reproduction of different phenotypes resulting from the interaction of organisms with their environment. **PROCESS**

  28. How Natural Selection Works

  29. For any alleles of a trait: frequency of the dominant allele is ‘p’ and the frequency of the recessive allele is ‘q’ And p + q = 1 (p + qalways equals1) And if you mate two organisms, you can mathematically determine the expectedproportion of offspring of each type p + q p + q p2 + 2pq + q2

  30. In a simple organism, p = q = 0.5 and p2 + 2pq + q2 = (0.5)(0.5) + 2 (0.5)(0.5) + (0.5)(0.5) = .25 +.5 +.25 This is the familiar 1:2:1 genotypic ratio for a simple monohybrid cross p2 2pq q2

  31. This idea holds true for any value of p or q. For example: If p is very common - say 90% of the genes in the population Then p = .9 and q = .1 And p2 = .81 (the frequency of the AA genotype) 2pq = .18 (the frequency of the Aa genotype) q2 = .01 (the frequency of the aa genotype)

  32. In the early 1900’s, Hardy and Weinberg used this idea to establish a fundamental idea in the genetic basis of natural selection

  33. The Hardy-Weinberg Equilibrium Assume that p = .6 and q = 0.4 In Generation 1 p2 + 2pq + q2 = .36 + .48 + .16 In Generation 2 p2 + 2pq + q2 = .36 + .48 + .16 In Generation 3 p2 + 2pq + q2 = .36 + .48 + .16 In Generation 4 p2 + 2pq + q2 = .36 + .48 + .16 • • •

  34. In any population, allelic and genotypic frequencies will remain the same if Mendelian inheritance patterns are the only factors at work No gene flow No mutations Very large population size Hardy-Weinberg Equilibriumassumes: No natural selection Random mating

  35. The Hardy-Weinberg Equilibrium 1. Large population sizes What happens if the population isn’t ‘large’? Genetic Drift - a statistic consequence of small populations

  36. The Hardy-Weinberg Equilibrium 1. Large population sizes What happens if the population isn’t ‘large’? Genetic Drift Bottlenecks

  37. The Hardy-Weinberg Equilibrium 1. Large population sizes What happens if the population isn’t ‘large’? Genetic Drift Bottlenecks Founder effect

  38. The Hardy-Weinberg Equilibrium 1. Large population sizes 2. Mutations - source of all new genetic variation How do we model this? Frequency of aa Frequency of AA Frequency of Aa Imagine that ‘A’ mutates to ‘a’ at a rate of m per generation Frequency of A after one generation of mutation Frequency of A after a second generation of mutation

  39. Imagine that ‘A’ mutates to ‘a’ at a rate of m per generation Frequency of A after one generation of mutation Substitute Frequency of A after a second generation of mutation For any number of generations (x)

  40. The Hardy-Weinberg Equilibrium 1. Large population sizes 2. Mutations - source of all new genetic variation 3. Random mating This assumes no preferences in mates Humans: Preferences Height - we tend to mate with people closer to our own height

  41. The Hardy-Weinberg Equilibrium 1. Large population sizes 2. Mutations - source of all new genetic variation 3. Random mating 4. Natural Selection -depends on variability that is heritable -differences must be passed to the offspring Key idea : Fitness: The contribution an individual makes to the gene pool of the next generation relative to other individuals Higher fitness Lower fitness

  42. Types of Natural Selection Most traits have a normal (or bell curve distribution)

  43. Types of Natural Selection 1. STABILIZING SELECTION

  44. Types of Natural Selection 1. STABILIZING SELECTION Human birth weight

  45. Types of Natural Selection 2. DIRECTIONAL SELECTION

  46. Types of Natural Selection 2. DIRECTIONAL SELECTION Salmon fishing - largest fish are taken every year

  47. Types of Natural Selection 3. DISRUPTIVE SELECTION

  48. Types of Natural Selection 3. DISRUPTIVE SELECTION

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