Evolutionary Psychology
Lecture 1 - Introduction
Standard explanations for human behaviour
Standard Social Science Model (SSSM)
1.
Animals are rigidly controlled by their biology, human
behaviour determined by culture.
2.
Human infants born with nothing apart from a few reflexes
and an ability to learn.
3.
Learning is a general purpose process used in all domains of
knowledge
4.
Children learn how to behave in their culture through
imitation, reward, and punishment.
Evolutionary Psychology
• Evolutionary Biology + Cognitive Psychology
• Goal is to understand the human mind/brain from an
evolutionary perspective
• The design of the mind must have been shaped by natural
selection (including sexual selection)
• Our mental lives and behavior reflect the evolutionary history
of our species, particularly the adaptive problems that had to
be solved
• The Pleistocene period: the “environment of evolutionary
adaptedness” or EEA (2 million – 10,000 years ago).
Characteristics of the EEA
The EEA probably consisted of:
• Hunter/gather/scavenging subsistence
• Nomadic or semi-nomadic
• Low population density
• Small kin-based groupings
• Simple technology
• High infant mortality and low life expectancy
• Vulnerability (e.g. predators, disease)
• Few lifestyle options.
• 10,000 years ago: development of agriculture => living in
large anonymous towns and cities.
What is evolution?
Evolutionary theory consists of several simple assumptions:
1.
Within a species there is heritable variability.
2.
Some variations result in more offspring (natural selection),
who will themselves possess these beneficial differences.
3.
Classical fitness = a measure of an individual’s direct
reproductive success
Inclusive fitness = a measure of an individual’s indirect
reproductive success (Hamilton 1964)
Sexual Selection
Evolution can be driven by mate preferences
Imagine some females prefer longer than average tails.
Their offspring will have larger than average tails and their
female offspring will fancy long tails.
The sons can have more than average offspring; and the
daughters will have sons similarly blessed.
 Positive feedback leading to runaway growth in tail length.
WHY should females prefer any particular trait (like long tails)?
Traits can be genetic fitness indicators – if a male can survive
despite a long tail, he must be better than average in other
respects.
Sexual selection produces
1. Rapid evolutionary change
2. Excessive and extravagant adaptations
3. Individual differences that are not eliminated by selection
4. Traits that make one a desirable partner
5. Traits rarely produced by convergent evolution
Miller (2000, the Mating Mind): All characteristics of
everything that makes us distinctively human! Our
intelligence, language, wit, art, creativity, and morality.
Our extravagant cognitive abilities evolved so we can chat
people up?
Adaptive Problems
• Our minds were designed by natural and sexual selection to
solve adaptive problems faced by our hunter-gatherer
ancestors.
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avoiding predators
eating the right food
attracting mates
forming alliances
“reading others people’s minds”
• All of these things are crucial for
passing on your genes. We
therefore expect selection to
have designed mental mechanisms to
solve these problems.
Adaptations
Evolution produces adaptations that on average increase
inclusive fitness.
We do not do those things that maximize fitness; we execute
those adaptations that in the past increased fitness.
WHY does a certain trait exist?
ULTIMATE CAUSE – the reason why it increased fitness in
the evolutionary past
PROXIMATE CAUSE – the immediate psychological,
physiological, biochemical, and environmental reasons
E.g. we eat because we are hungry, have sex because we
desire it, help people because we feel compassion,
withdraw because we feel sad – we do not calculate the
effect of our behaviour on inclusive fitness! (We do not
need to be aware of ultimate reasons to behave adaptively.)
Are all behaviours adaptive?
Evolutionary psycholgists habitiually look first to adaptive explanations.
E.g. Rape - most social scientists try to explain this behaviour as “maladaptive”
but evolutionary psychologists indicate possible adaptive benefits.
•
Homosexuality – bisexuality is selected for, and a side effect is some
people being 100% homosexual?
It is not always possible to explain behaviours as “adaptive” and we must take
into account the following:
1.
In some cases the environment may change more rapidly than the organism
can evolve.
2.
An adaptation is not always adaptive in every circumstance.
“Naïve adaptationism” (Gould and Lewontin, 1979)
It is easy to invent “just so” stories to explain why
something evolved. But:
- not all characteristics of an evolved structure are
adaptive per se (e.g. the redness of blood, two nipples
rather one?) and some features will arise because of
physical constraints (hexagonal honeycombs), or as
side effects.
- when postulating an ultimate (adaptive) explanation,
draw predictions and seek to test them
Some people take Gould and Lewontin too strongly.
Adaptation produced by selection is the only means
for producing increasingly complex structures.
Adaptive thinking can be insightful (for which organism is fever
adaptive?)
Questions Asked
1.
What selection pressures are most relevant to
understanding the adaptive problem under consideration?
2.
What psychological mechanisms have evolved to solve
that adaptive problem?
3.
What is the relationship b/w the structure of these
psychological mechanisms and human culture?
Insights From Evolutionary Psychology
1. Our mind consists of a set of domain specific information
processing modules; e.g. language, theory of mind,
perception.
2. Food preferences: Strong desire for fat was once very
adaptive, no longer so.
(Speculation: An environment in which food is only
periodically available – e.g. by dieting - means it is adaptive
to switch on more fat storage)
3. Reasoning: We are good at reasoning about problems relevant
to the EEA: cheater detection (Cosmides & Tooby, 1992)
4. Perception: Our colour vision is adapted to seeing ripe/unripe
fruits against background foliage
5. Memory: Our forgetting rates are adaptive (Roland)
6. Mood: Evolution has no interest in maximizing happiness!
Anxiety: Makes us cautious about actions we should be cautious
about
Sadness: Makes us withdraw from situations in which we might
suffer further loss
Anger and kindness: Produce the effective tit for tat style of
negotiation
7. Mental disorders
Phobias : fear of snakes vs. fear of guns
Depression: Should withdraw from a major life endeavour and
start a new one?
(http://www-personal.umich.edu/~nesse/publications.htm)
8. Men and women’s mate preferences and sexual strategies
Moral reactions against evolutionary psychology:
Aren’t evolutionary psychologists Daily-Mail-reading
crypto-conservatives opposed to social change?
The Naturalist Fallacy: You cannot derive an “ought” from
an “is”. (Just because we have genetic tendencies to have
affairs, that does not mean we should. Just because there
are differences between the genders, that does not mean it
is right to be sexist.)
Further, you cannot derive an “is” from an “ought”: The
outcome of scientific research cannot be determined by
what you think it morally should be.
We are not slaves to our genes:
Natural selection operates on units other than genes.
Evolution occurs when there are more or less faithful “replicators”
(carried in vehicles) subject to selective pressures.
The replicators can be memes rather than genes: An element of
culture that can be passed on by imitation (Dawkins, 1976).
There is competition by memes to be housed in our limited brains;
those memes good at replication can invade many brains.
Blackmore, S. (1999) “The meme machine”:
Why can’t we stop thinking? We are we altruistic? Why does
language exist? What attracts us to our mates? Why is religion so
universal? What is a self?