Download Evolutionary Theory Nature and Nurture The 3 Premises of Natural

Evolutionary Theory
• Who are the two founders of evolutionary theory?
• Explain the logic of natural selection.
• What is the difference between genotype and phenotype?
• What are the three main categories of adaptive problems?
• What is the difference between proximate and ultimate
explanations? Are they alternatives or complementary?
• Give examples of Tinbergen’s four whys.
• What are the three types of natural selection?
• Explain the difference between adaptive behaviour and
behavioural adaptation.
• Why is the differential reproduction of organisms more
important than their differential survival?
• Compare sexual selection and natural selection.
The 3 Premises of Natural Selection
1.The Principle of Variation
Individuals in a population have variation in their physical
and behavioural traits (i.e., phenotype)
2.The Principle of Inheritance
Some of this variation is heritable (i.e., due to genotype)
3.The Principle of Adaptation
Variation can help individuals to compete
Nature and Nurture
Nobody really believes
that all of human
behaviour is innate (i.e.,
can be explained by
genes with no input from
the environment).
Similarly, nobody believes
that the environment
determines all behaviour
without constraints of
biology.
Adaptive Problems in Human Evolution
• Survival
• Finding, choosing, processing appropriate food
• Avoiding predators
• Combating pathogens
• Keeping warm
• Reproduction
• Choosing & wooing appropriate mates
• Competing with same-sex rivals
• Scheduling births
• Caring for children
• Sociality
• Helping relatives & allies, cooperating & co-ordinating
• Avoiding exploitation (selective allocation of help)
• Learning & teaching: sharing information & skills
• Political alliance & between-group conflicts
Charles Darwin
Alfred Russel Wallace
Levels of Explanation
• Proximate - How?
• How do the environment and the individual’s genetic
make-up interact to produce this behaviour?
• What body systems (nervous, hormonal, etc.) are
involved in this behaviour?
• Ultimate - Why?
• What is the function?
• How does/did this trait help individuals increase their
genetic representation in future generations?
• What environmental pressures selected for this trait?
• How has this behaviour changed over evolutionary
history?
Tinbergen’s Four Whys
1. Proximate or mechanistic cause
The baby was crying
Breasts were full of milk
2. Ontogenetic or developmental or cause
Mother learned to nurse by observation
Behaviours may be prepared by hormones
3. Phylogenetic or historical cause
All mammals produce milk to feed offspring
Explanations for how mammals evolved
4. Ultimate or functional cause
Nursing promotes the survival of offspring
Types of Natural Selection
Evolutionary adaptation is a special and
onerous concept that should not be used
unnecessarily, and an effect should not be
called a function unless it is clearly produced
by design and not by chance. When
recognized, adaptation should be attributed to
no higher a level of organization than is
demanded by the evidence.
George Williams
Evidence of Design
Evidence of Design
Gecko walking
upside down
on glass
Lamellae on
gecko toes
Magnified hairs
Gecko foot
Autumn et al. (2002) Proc Nat Acad Sci
Inferring Function from Structure
Functions of Pregnancy Sickness
miscarriages
fetal deaths
20%
15%
10%
5%
0%
NVP absent
Nausea Only
Vomiting
(Flaxman & Sherman 2000)
Does Adaptation = Adaptive?
NO.
Change in the environment is a
major reason why an adaptation
may not be currently adaptive.
Behaviour resulting in an adaptive outcome is
not necessarily the result of a psychological
adaptation.
This is why we need the criterion of complex
design to identify adaptations.
Basis of Sexual Selection
Survival of the Fittest?
Natural selection favours traits that help organisms to
increase their genetic representation in future generations.
Traits increasing reproduction will be favoured over traits
increasing survival if the two are in conflict. Survival is only
useful to an organism inasmuch as
it is correlated with increased
reproduction.
Sexual selection is often seen as
separate from natural selection
because it commonly results in
adaptations that reduce survival.
Types of Sexual Selection
Darwin noted that aggressive competition for mates is mainly a
male affair, whereas mate choice is exercised mainly by
females. But he had no explanation.
Intersexual Selection
Bateman (1948) was the first to recognize that males can often
gain fitness more or less linearly by mating with more females,
whereas females seldom profit similarly from extra mates.
Members of one sex
choose members of
the other sex
Williams (1966) and Trivers (1972)
expanded on Bateman’s argument,
noting that the sex difference in
parental investment is not solely a
matter of anisogamy.
Anisogamy: an ovum is much larger
than a sperm.
Reproductive Variance in Fruit Flies
Intrasexual Selection
Members of one sex
compete for access to
members of the other sex
Reproductive Variance in Humans
Lifetime reproduction for
birth cohorts of 100 !
Kung San of each sex,
living as traditional
hunter-gatherers in the
Kalahari desert
(Howell 1979)
Males have more offspring per additional mate, more mates,
and more variance in number of mates
(Bateman 1948)
Number of living children as a
function of number of wives /
co-wives for the Temne of
Sierra Leone
(Dorjahn 1958)
Human Mating Systems
Polygyny
Marriage system:
whether a culture allows
men and/or women to
have more than one
official mate
(708)
Effective mating system:
(4)
Polyandry
male fitness variance
female fitness variance
(137)
Monogamy
(Murdock 1967)
Vocabulary
• Adaptation
• Adaptive
• Alfred Russel Wallace
• Anisogamy
• Charles Darwin
• Directional Selection
• Disrupting Selection
• Effective mating system
• Fitness
• Genotype
• Heritable
• Innate
• Monogamy
• Natural Selection
• Naturalistic Fallacy
• Ontogenetic
• Operational Sex Ratio
• Phenotype
• Phylogenetic
• Polyandry
• Polygyny
• Proximate
• Reproductive Variance
• Sexual Dimorphism
• Sexual Selection
• SSSM
• Stabilising Selection
• Ultimate
Sexual Dimorphism