Evolution: An Idea in Three Parts

1. Evolution: An Idea in Three Parts

2. Part one: The Organic Origins Debate and the “Darwin Wars”

3. Defining the Period • Simplification of the Victorian era: • Prudish • Sexist • Racist • Science vs. Revealed & Natural religion

4. Defining the Problem • Extinction • Catastrophism vs. Uniformatism: • Earth was created by a series of rapid, catastrophic events • Earth was created through slow, naturally occurring processes • Introduction of new species in foreign environments

5. The Argument from Design (1) • Many things in this world do not appear to be accidents, but seem “designed” • A discovered watch demonstrates design • To be designed, there must be a Designer

6. The Argument from Design (2) • David Hume: • Scathing critique of the argument from design by extending the argument to its logical conclusions • Infinite regress of intelligent designers, intelligence as a “superior” function • Nonetheless, design still prevailed...

7. The Evolutionists • Erasmus Darwin • Etienne Geoffroy Saint-Hilaire • Jean Baptiste de Lamarck • Robert Chambers • Charles Lyell (?) • Joseph Dalton Hooker

8. The Critics • Georges Cuvier • John F. W. Herschel • William Whewell • Rev. Adam Sedgwick • Hugh Miller • St. George Jackson Mivart

9. Charles Robert Darwin • Well-off • Not originally a good student • Specialised in Geology • Researched in the Galápagos

10. Alfred Russell Wallace • Humble beginnings • Amateur collector of specimens • Lost virtually all of his collection in a fire • He may have been an evolutionist because he was not an academic

11. Richard Owen • Comparative anatomist • Darwin & Huxley were originally indebted to him • Developed a theory of Archetypes and introduced the term Homology to biology

12. Thomas Henry Huxley • Modest family background, supported by scholarship in medical school • “Darwin’s Bulldog,” vicious critic of others • Persuaded by evolutionary thinking • Destroyed Owen’s Archetypal theory

13. Social Darwinism & Eugenics • Inspired by the works of Spencer & Galton • Committed several logical errors: • Naturalistic fallacy • Genetic determinism • Progression • Led to sterilizations, discrimination

14. Fast-Forward: Sociobiology (1) • In the 1960s and 1970s • Attempted to apply selectionist thinking to animal behaviour • E.O. Wilson and Sociobiology: The New Synthesis, final chapter on humans

15. Fast-Forward: Sociobiology (2) • Vitriolic reaction • Criticisms of sociobiological analyses: • genetic determinism • racism • sexism • The question remains whether these criticisms actually hold up to scrutiny

16. Part two: Evolutionary Theory

17. Lamarckian Evolution (1) • Acquired characteristics & satisfaction of needs • Saltationist • Scala Naturae: • Organisms move progressively up evolutionary scale, with irregularities • Multiple concurrent phylogenetic lines

18. Lamarckian Evolution (2) a b c d a’ b c Ø a a’ b Ø a a’ Ø a Ø Adapted from Ruse (1999)

19. Lamarckian Evolution (3) • Problems: • Poor mechanism for speciation • Lacking a model of inheritance • No evidence of spontaneous generation • No evidence of spontaneous speciation • Does not follow the fossil record (though he never claimed it did)

20. Darwinian Evolution (1) • Influences: • Malthus and struggle for survival • Lyellian uniformitarianism • Animal breeding • Varieties & species of the Galápagos

21. Darwinian Evolution (2) • “Descent with modification” • Gradual adaptation to environment • Variation, inheritance, & differential reproduction • Common descent

22. Darwinian Evolution (3) a b c d a’ Adapted from Ruse (1999) Ø

23. Darwinian Evolution (4) • Types of selection: • Natural • Sexual • Artificial • Pangenesis model of inheritance: • Gemmules • Blended • Acquired

24. Darwinian Evolution (5) • Problems: • Blended inheritance • Acquired characteristics • Geological time scale for selection (lack of scientific knowledge of the time) • Mate choice and sexual selection (not well accepted at the time)

25. Mendelian Genetics • Gregor Mendel, an Austrian monk, was the discoverer of the basis of heredity • Ignored in Darwin’s time (and by Darwin himself!) • Solved the problem of inheritance by demonstrating that it was particulate in nature, not “blended”

26. The Modern Synthesis • Until the 1930s, Lamarckianism was the most commonly accepted theory • The foundations of the modern synthesis, based on Darwin’s model, were laid by several key biologists: • Ronald Fisher • Sewall Wright • J.B.S. Haldane

27. Fitness • The relative number of surviving offspring • More particularly: • the extent to which copies of an individual’s genotype are present in succeeding generations, relative to other genotypes • Does not refer to physical well-being or degree of adaptation to the environment

28. Adaptation (1) • An idiosyncrasy of structure, physiology, or behaviour that aids an organism in its environment • Environments are both physical (e.g., ecosystem) and biological (other organisms)

29. Adaptation (2) • A slow process over many generations • Environmentally-specific • Adaptations may be out-of-date • Cumulative

30. Natural Selection • Differential rate of reproduction and survival of different genotypes in a population • Responsible for adaptation to environment by selecting complete phenotypes • Selects & maintains adaptations

31. Types of Selection (1) μø • Stabilising: • Always taking place • Eliminates extreme individuals in a population μn

32. Types of Selection (2) μø • Disruptive: • Increases extreme forms in a population at the expense of intermediate ones • Responsible for “group” differences (e.g., males vs. females) μn

33. Types of Selection (3) μø • Directional: • Increases one extreme form at the expense of other forms in the population • Generally responsible for speciation μn

34. Types of Selection (4) • Frequency-dependent: • Acts on multiple phenotypes in a population • Works by decreasing more common types and increasing less common types, due to intra-typical competition • This continues until an equilibrium of sorts is reached

35. Types of Selection (5)* • Sexual Selection: • Darwin originally conceived of Sexual Selection as a mechanism separate from, but complementary to, NS: • Referred to selection through competition for reproduction • However, since NS now encompasses bothsurvival and reproduction, SS is now seen as a fifth type of NS

36. Sexual Selection • Definition: • Differential rate of reproduction of different genotypes in a population in the context of mating • Types of mating contexts: • Intersexual • Intrasexual

37. Part three: The Philosophy of Evolutionary Theory

38. Levels of Causation • Proximate causation: • “How?” questions • Explains how a mechanism works • Ultimate causation: • “Why?” questions • Explains why a mechanism exists and what function it serves

39. Levels of Selection (1) • “Good of the species” thinking is outdated • Inclusive Fitness (Kin Selection) theory: • Fitness is based on the adaptiveness of a gene in an organism and copies of that gene in related organisms

40. Levels of Selection (2) • The Price Equation (equivalence principle): • Mathematical formulation for evolutionary change • Allows one to solve complex evolutionary problems using different levels of selection • Arguments are now being made to utilise multi-level selectionist thinking

41. The Calculus of Selection • Selection operates on the basis of costs & benefits • r-K selection: • r = rapid and large production of offspring, short lifespan • K = slow and small production of offspring, long lifespan • Predicted by stability of environment (.e.g, safety of offspring)

42. The Problem of Fitness • Spencer’s quote, “survival of the fittest,” is misleading • Survival is important only insofar that it helps to increase fitness • Fitness is measured only in reproductive terms: • relative number of copies of a genotype in succeeding populations

43. OGOD Hypothesis • “One Gene, One Disorder” thinking is also outdated • Although the phenomenon of OGOD does take place in certain circumstances, most behaviour is multiply-caused

44. Evolution and Deism • Evolutionary theory does not discredit belief in God, per se • It does, however, counter literal readings of any major religious text • Science is a philosophical model that does not subscribe to supernatural circumstances in order to explain phenomena

45. The Naturalistic Fallacy (1) • “It is demonstrated… that things cannot be otherwise: for, since everything was made for a purpose, everything is necessarily for the best purpose. Note that noses were made to wear spectacles; we therefore have spectacles.” -Dr. Pangloss, from Voltaire’s Candide

46. The Naturalistic Fallacy (2) • The confusion of an “is” statement with an “ought” statement • Scientific descriptions of the natural world cannot tell us what ought to be, only what is • We, as a people, are responsible for defining out morals and ethical practices, regardless of our ancestral heritage

47. Progress & Foresight • Lamarck incorrectly envisioned evolution as a ladder, with humans on top • Selection works on short-term consequences • Selection has no foresight • As Darwin said, “It is absurd to talk of one animal being higher than another” (Species Notebook B)

48. Genetic Determinism • The idea that genes alone are necessary and sufficient causes for all behaviour • A major criticism of evolutionary research applied to humans: • Fueled the “nature-nurture” debate • However, very little modern-day evolutionary research is genetically deterministic

49. The Wrap-Up (1) • Part one: History • The problem of organic origins • The flaws of the Argument from Design • The evolutionists and their critics • Social Darwinism & Eugenics • The “Darwin Wars” and Sociobiology

50. The Wrap-Up (2) • Part two: Evolutionary theory • Lamarckian vs. Darwinian theory • Mendelian genetics and particulate inheritance • The Modern Synthesis: • Adaptation • Fitness • Five types of Natural Selection