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Evolution: An Idea in Three Parts. Part one:. The Organic Origins Debate and the “Darwin Wars”. Defining the Period. Simplification of the Victorian era: Prudish Sexist Racist Science vs. Revealed & Natural religion. Defining the Problem. Extinction Catastrophism vs. Uniformatism:

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part one

Part one:

The Organic Origins Debate and the “Darwin Wars”

defining the period
Defining the Period
  • Simplification of the Victorian era:
    • Prudish
    • Sexist
    • Racist
  • Science vs. Revealed & Natural religion
defining the problem
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
the argument from design 1
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
the argument from design 2
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...
the evolutionists
The Evolutionists
  • Erasmus Darwin
  • Etienne Geoffroy Saint-Hilaire
  • Jean Baptiste de Lamarck
  • Robert Chambers
  • Charles Lyell (?)
  • Joseph Dalton Hooker
the critics
The Critics
  • Georges Cuvier
  • John F. W. Herschel
  • William Whewell
  • Rev. Adam Sedgwick
  • Hugh Miller
  • St. George Jackson Mivart
charles robert darwin
Charles Robert Darwin
  • Well-off
  • Not originally a good student
  • Specialised in Geology
  • Researched in the Galápagos
alfred russell wallace
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
richard owen
Richard Owen
  • Comparative anatomist
  • Darwin & Huxley were originally indebted to him
  • Developed a theory of Archetypes and introduced the term Homology to biology
thomas henry huxley
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
social darwinism eugenics
Social Darwinism & Eugenics
  • Inspired by the works of Spencer & Galton
  • Committed several logical errors:
    • Naturalistic fallacy
    • Genetic determinism
    • Progression
  • Led to sterilizations, discrimination
fast forward sociobiology 1
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
fast forward sociobiology 2
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
part two

Part two:

Evolutionary Theory

lamarckian evolution 1
Lamarckian Evolution (1)
  • Acquired characteristics & satisfaction of needs
  • Saltationist
  • Scala Naturae:
    • Organisms move progressively up evolutionary scale, with irregularities
    • Multiple concurrent phylogenetic lines
lamarckian evolution 2
Lamarckian Evolution (2)

a

b

c

d

a’

b

c

Ø

a

a’

b

Ø

a

a’

Ø

a

Ø

Adapted from Ruse (1999)

lamarckian evolution 3
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)
darwinian evolution 1
Darwinian Evolution (1)
  • Influences:
    • Malthus and struggle for survival
    • Lyellian uniformitarianism
    • Animal breeding
    • Varieties & species of the Galápagos
darwinian evolution 2
Darwinian Evolution (2)
  • “Descent with modification”
  • Gradual adaptation to environment
  • Variation, inheritance, & differential reproduction
  • Common descent
darwinian evolution 3
Darwinian Evolution (3)

a

b

c

d

a’

Adapted from Ruse (1999)

Ø

darwinian evolution 4
Darwinian Evolution (4)
  • Types of selection:
    • Natural
    • Sexual
    • Artificial
  • Pangenesis model of inheritance:
    • Gemmules
    • Blended
    • Acquired
darwinian evolution 5
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)
mendelian genetics
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”
the modern synthesis
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
fitness
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
adaptation 1
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)
adaptation 2
Adaptation (2)
  • A slow process over many generations
  • Environmentally-specific
    • Adaptations may be out-of-date
  • Cumulative
natural selection
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
types of selection 1
Types of Selection (1)

μø

  • Stabilising:
    • Always taking place
    • Eliminates extreme individuals in a population

μn

types of selection 2
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

types of selection 3
Types of Selection (3)

μø

  • Directional:
    • Increases one extreme form at the expense of other forms in the population
    • Generally responsible for speciation

μn

types of selection 4
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
types of selection 5
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
sexual selection
Sexual Selection
  • Definition:
    • Differential rate of reproduction of different genotypes in a population in the context of mating
  • Types of mating contexts:
    • Intersexual
    • Intrasexual
part three

Part three:

The Philosophy of Evolutionary Theory

levels of causation
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
levels of selection 1
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
levels of selection 2
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
the calculus of selection
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)
the problem of fitness
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
ogod hypothesis
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
evolution and deism
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
the naturalistic fallacy 1
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

the naturalistic fallacy 2
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
progress foresight
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)
genetic determinism
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
the wrap up 1
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
the wrap up 2
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
the wrap up 3
The Wrap-Up (3)
  • 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
things to come
Things to Come
  • Human origins
  • Genetics:
    • Mathematics of inheritance
    • Structure and functioning of DNA
    • Sex chromosomes
    • Implications