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Evolution: An Idea in Three Parts. Part one: The Organic Origins Debate and the “Darwin Wars”

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Presentation on theme: "Evolution: An Idea in Three Parts. Part one: The Organic Origins Debate and the “Darwin Wars”"— Presentation transcript:

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

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) Ø Ø Ø Ø abc d a a a a’ b b c Adapted from Ruse (1999)

19 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) Lamarckian Evolution (3)

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

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

22 Darwinian Evolution (3) Ø abc d a’ Adapted from Ruse (1999)

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

24 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) Darwinian Evolution (5)

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 A slow process over many generations Environmentally-specific  Adaptations may be out-of-date Cumulative Adaptation (2)

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 Stabilising:  Always taking place  Eliminates extreme individuals in a population Types of Selection (1) μøμø μnμn

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

33 Directional:  Increases one extreme form at the expense of other forms in the population  Generally responsible for speciation Types of Selection (3) μøμø μnμn

34 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 Types of Selection (4)

35 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 both survival and reproduction, SS is now seen as a fifth type of NS Types of Selection (5)*

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

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 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 Levels of Selection (2)

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 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 The Naturalistic Fallacy (2)

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

51 Part three: Philosophy of Evolution  Ultimate vs. Proximate causation  Levels of selection  Costs & benefits  Problems & fallacies: Survival of the fittest, OGOD, evolution vs. deism, progress & foresight, genetic determinism The Wrap-Up (3)

52 Things to Come Human origins Genetics:  Mathematics of inheritance  Structure and functioning of DNA  Sex chromosomes  Implications

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