Transcript Lecture 2 - Organic Origins Debate

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:
 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)

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)

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
Erasmus Darwin
 Etienne Geoffroy Saint-Hilaire
 Jean Baptiste de Lamarck
 Robert Chambers
 Charles Lyell (?)
 Joseph Dalton Hooker

The Critics
Georges Cuvier
 John F. W. Herschel
 William Whewell
 Rev. Adam Sedgwick
 Hugh Miller
 St. George Jackson Mivart

Charles Robert Darwin

Well-off

Not originally a good student

Specialised in Geology

Researched in the Galápagos
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

Comparative anatomist

Darwin & Huxley were originally indebted
to him

Developed a theory of Archetypes and
introduced the term Homology to biology
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

Inspired by the works of Spencer & Galton

Committed several logical errors:
 Naturalistic fallacy
 Genetic determinism
 Progression

Led to sterilizations, discrimination
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)
Vitriolic reaction
 Criticisms of sociobiological analyses:
 genetic determinism
 racism
 sexism
 The question remains whether these
criticisms actually hold up to scrutiny

Part two:
Evolutionary Theory
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)
a
b
Ø
c
d
a’
b
c
a
a’
b
a
a’
Ø
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Adapted from Ruse (1999)
a
Ø
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)

Influences:
 Malthus and struggle for survival
 Lyellian uniformitarianism
 Animal breeding
 Varieties & species of the Galápagos
Darwinian Evolution (2)

“Descent with modification”

Gradual adaptation to environment

Variation, inheritance, & differential
reproduction

Common descent
Darwinian Evolution (3)
a
b
c
d
a’
Adapted from Ruse (1999)
Ø
Darwinian Evolution (4)
Types of selection:
 Natural
 Sexual
 Artificial
 Pangenesis model of inheritance:
 Gemmules
 Blended
 Acquired

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
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
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
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)

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)

A slow process over many generations

Environmentally-specific
 Adaptations may be out-of-date

Cumulative
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)

μø
Stabilising:
 Always taking place
 Eliminates extreme
individuals in a population
μn
Types of Selection (2)

Disruptive:
 Increases extreme forms
in a population at the
expense of intermediate
ones
 Responsible for “group”
differences (e.g., males
vs. females)
μø
μn
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)

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)*

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
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:
The Philosophy of
Evolutionary Theory
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)

“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)
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

Selection operates on the basis of costs &

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)
benefits
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

“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
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)

“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 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
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
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)

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)

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)

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
Human origins
 Genetics:
 Mathematics of inheritance
 Structure and functioning of DNA
 Sex chromosomes
 Implications
