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)

Ø

Ø

Ø

Ø

a b c d

a

a

a

a’

a’

a’

b

b

c

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)

Ø

a b c d

a’

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