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Evolution: Evolution:
An Idea in Three An Idea in Three PartsParts
Part one:Part one:The Organic Origins
Debate and the “Darwin Wars”
Defining the PeriodDefining the Period
Simplification of the Victorian era:PrudishSexistRacist
Science vs. Revealed & Natural religion
Defining the ProblemDefining the Problem
ExtinctionCatastrophism 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 The Argument from Design (1)(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 The Argument from Design (2)(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 EvolutionistsThe Evolutionists
Erasmus DarwinEtienne Geoffroy Saint-HilaireJean Baptiste de LamarckRobert ChambersCharles Lyell (?)Joseph Dalton Hooker
The CriticsThe Critics
Georges CuvierJohn F. W. HerschelWilliam WhewellRev. Adam SedgwickHugh MillerSt. George Jackson Mivart
Charles Robert DarwinCharles Robert Darwin
Well-off
Not originally a good student
Specialised in Geology
Researched in the Galápagos
Alfred Russell WallaceAlfred 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 OwenRichard Owen
Comparative anatomist
Darwin & Huxley were originally indebted to him
Developed a theory of Archetypes and introduced the term Homology to biology
Thomas Henry HuxleyThomas 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 & EugenicsSocial 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 Fast-Forward: Sociobiology (1)(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
Vitriolic reactionCriticisms of sociobiological analyses:
genetic determinism racismsexism
The question remains whether these criticisms actually hold up to scrutiny
Fast-Forward: Sociobiology Fast-Forward: Sociobiology (2)(2)
Part two:Part two:
Evolutionary Theory
Lamarckian Evolution (1)Lamarckian Evolution (1)
Acquired characteristics & satisfaction of needs
SaltationistScala Naturae:
Organisms move progressively up evolutionary scale, with irregularities
Multiple concurrent phylogenetic lines
Lamarckian Evolution (2) Lamarckian Evolution (2)
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a b c d
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a
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a’
a’
b
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Adapted from Ruse (1999)
Problems:Poor mechanism for speciationLacking a model of inheritanceNo evidence of spontaneous
generationNo evidence of spontaneous
speciationDoes not follow the fossil record
(though he never claimed it did)
Lamarckian Evolution (3) Lamarckian Evolution (3)
Darwinian Evolution (1)Darwinian Evolution (1)
Influences:Malthus and struggle for survivalLyellian uniformitarianismAnimal breedingVarieties & species of the
Galápagos
“Descent with modification”
Gradual adaptation to environment
Variation, inheritance, & differential reproduction
Common descent
Darwinian Evolution (2)Darwinian Evolution (2)
Darwinian Evolution (3)Darwinian Evolution (3)
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Adapted from Ruse (1999)
Types of selection:NaturalSexualArtificial
Pangenesis model of inheritance:GemmulesBlendedAcquired
Darwinian Evolution (4)Darwinian Evolution (4)
Problems:Blended inheritanceAcquired characteristicsGeological 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)Darwinian Evolution (5)
Mendelian GeneticsMendelian 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 SynthesisThe 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 FisherSewall Wright J.B.S. Haldane
FitnessFitness
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)
A slow process over many generations
Environmentally-specificAdaptations may be out-of-date
Cumulative
Adaptation (2)Adaptation (2)
Natural SelectionNatural 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
Stabilising:Always taking placeEliminates extreme individuals in a population
Types of Selection (1)Types of Selection (1) μø
μn
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)Types of Selection (2) μø
μn
Directional: Increases one extreme
form at the expense of other forms in the population
Generally responsible for speciation
Types of Selection (3)Types of Selection (3) μø
μn
Frequency-dependent:Acts on multiple phenotypes in a
populationWorks 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)Types of Selection (4)
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)*Types of Selection (5)*
Definition:Differential rate of reproduction of
different genotypes in a population in the context of mating
Types of mating contexts: Intersexual Intrasexual
Sexual SelectionSexual Selection
Part three:Part three:
The Philosophy of Evolutionary Theory
Levels of CausationLevels of Causation
Proximate causation:“How?” questionsExplains how a mechanism works
Ultimate causation:“Why?” questionsExplains 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
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)Levels of Selection (2)
The Calculus of SelectionThe 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 FitnessThe 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 HypothesisOGOD 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 DeismEvolution 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 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)The Naturalistic Fallacy (2)
Progress & ForesightProgress & Foresight
Lamarck incorrectly envisioned evolution as a ladder, with humans on top
Selection works on short-term consequences
Selection has no foresightAs Darwin said, “It is absurd to talk of
one animal being higher than another” (Species Notebook B)
Genetic DeterminismGenetic 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: HistoryThe problem of organic originsThe flaws of the Argument from
DesignThe evolutionists and their criticsSocial Darwinism & EugenicsThe “Darwin Wars” and
Sociobiology
Part two: Evolutionary theoryLamarckian vs. Darwinian theoryMendelian genetics and particulate
inheritanceThe Modern Synthesis:
AdaptationFitnessFive types of Natural Selection
The Wrap-Up (2)The Wrap-Up (2)
Part three: Philosophy of EvolutionUltimate vs. Proximate causationLevels of selectionCosts & benefitsProblems & fallacies:
Survival of the fittest, OGOD, evolution vs. deism, progress & foresight, genetic determinism
The Wrap-Up (3)The Wrap-Up (3)
Things to ComeThings to Come
Human originsGenetics:
Mathematics of inheritanceStructure and functioning of DNASex chromosomes Implications
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