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Evolutionary Psychology
Modern skulls house a
stone age mind
Basics of Evolutionary
Psychology
1. Evolutionary Psychologists argue that
natural selection designed our minds
to deal with problems that we faced on
the African savannahs.
– The savannah was our Environment of
Evolutionary Adaptedness (EEA).
Environment of Evolutionary
Adaptedness (EEA)
•
Therefore our mind consists of a collection of
adaptations. Each individual adaptation has
evolved to meet challenges faced in our EEA.
•
"a characteristic that has arisen through and been
shaped by natural and or sexual selection. It
regularly develops in members of the same species
because it helped to solve problems of survival and
reproduction in the evolutionary ancestry of the
organism. Consequently it can be expected to have
a genetic basis ensuring that the adaptation is
passed through the generations." (Williams, 1966)
The three products of
evolution
• Adaptations: Inherited and reliably developing
characteristics that came into existence through
natural selection because they aided in solving
problems related to survival and/or reproduction.
• Example: umbilical cord
• By-products: Characteristics that do not solve
adaptive problems and do not have functional design.
They are coupled to adaptations.
• Example: belly button
• Noise:Random effects produced by genetic drift and
chance mutations that do not affect survival and/or
reproductive success.
Behavioral tendencies as
adaptations
• It can be shown that humans have evolved
physiological traits in response to adaptive
pressures.
• The brain is the basis of all behavior, and the
brain is a physiological structure that has
evolved over time.
• Therefore, the product of the brain, human
behavior, has evolved certain characteristics
as well to better meet the demands of the
environment.
• We can see the cumulative effects of
selective pressures when we observe human
behavior.
Evolved Psychological
Mechanisms (Modules)
• An evolved psychological mechanism EPM
exists in the form that is does because it
solved a specific adaptive problem.
• EPM’s respond to a narrow range of stimuli.
• Input of an EPM orients the organism to the
adaptive problem it is facing.
• Example: pizza smell vs. snake
• Input to an EPM is subject to decision rules
before producing output.
– Decision rules: if-then statements based upon
experience
EPM’s
• Output can be either physiological activity,
cognitive processing or behavior.
• Output is directed towards solving the
adaptive problem.
• Important Point: EPM’s that led to effective
solutions in the past may no longer be
effective now (vestigial).
– Example: piloerrection (I.e. goose bumps)
EPM’s lead to behavioral
flexibility
• EPM’s are not rigid instincts, they
depend upon modulation by the
environment.
– E.g., Language.
• Decision rules create response options.
• EPM’s cut down on learning time and
constrain behaviors into a range that
inhibits behaviors that are maladaptive.
Example
• Imagine a population of omnivores that lacked the
capability to digest rancid meat.
– The byproducts of bacterial activity in rancid meat are
therefore toxic to this species.
• Imagine that this species had no EPM to stimulate
avoidance of rancid meat.
• Each individual would have to learn through trial and
error what smells, tastes etc… signaled that meat
was not fit for consumption.
• Now imagine that certain individuals were born with
an aversion to the smell of rancid meat.
• Which individuals would have a higher fitness?
The Standard Social Science
Model (SSSM) and Evolutionary
Psychology (EP)
• SSSM is the prevailing orthodoxy in
anthropology, sociology, and has dominated
psychology since the 1940's.
• The SSSM is under challenge from
Evolutionary Psychology (EP) which has
mounted a critique of contemporary
psychology because it has largely ignored the
role of evolution in shaping human behavior.
According to the SSSM:
According to EP:
Body structure (e.g. hands, kidneys, eyes)
has evolved
Body structure (e.g. hands, kidneys, eyes) has
evolved
There are several types of scientific
Endeavour e.g. natural sciences (biology,
botany, zoology etc.); social sciences
(sociology, psychology, politics etc.)
All science is a single coherent entity consisting of
many disciplines e.g. physics, biology, psychology,
sociology etc. - all characterized by adoption of the
scientific method.
Psychology is a social science. Social
sciences are concerned with how culture
and experience produce wide variation in
human behavior. Therefore social sciences
do not need to consider the role of
evolution in the development of behavioral
variability.
Biology is a natural science. Biology is built upon the
rock of evolutionary theory. Psychology is a branch
of biology.
Animal behavior is controlled by their
biology. Human behavior is determined by
culture and experience. Animal behavior is
more appropriately studied by biologists.
Animal and human behavior are biological
phenomena that have evolved.
Ignorance of evolutionary theory can lead some
psychologists to appear to view humans as having
progressed to be above apes and other 'lower'
animals on a 'scale of nature' or scala naturae.
Humans are born with a few reflexes and
the ability to learn. Essentially we are
'empty computers' or 'blank slates' at
birth, written on by the hand of culture
and experience.
Fodor (1998) expresses this idea as
follows:
"Most cognitive scientists still work in a
tradition of empiricism and
associationism whose main tenets
haven't changed much since Locke and
Hume. The human mind is a blank slate
at birth. Experience writes on the slate,
and association extracts and
extrapolates whatever trends there are in
the record that experience leaves. The
structure of the mind is thus an image,
made a posteriori, of the statistical
regularities in the world in which it finds
itself. I would guess that quite a
substantial majority of cognitive
scientists believe something of this sort;
so deeply, indeed, that many hardly
notice that they do."
The human mind consists of specialized
modules that are innate and have
evolved via natural and sexual selection
to cope with adaptive problems. Modules
resemble debugged computer programs
designed for a particular process e.g.
word processor, spreadsheet, database.
Fodor (1998) writes that evolutionary
psychologists view
"..the mind as computational system; the
mind is massively modular; a lot of
mental structure, including a lot of
cognitive structure, is innate; a lot of
mental structure, including a lot of
cognitive structure, is an evolutionary
adaptation - in particular, the function of
a creature's nervous system is to abet
the propagation of its genome (its selfish
gene, as one says)."
Human behavior is controlled by a
general purpose systems which rely
on imitation, general intelligence,
culture, reward and punishment. These
systems are content-independent or
domain-general.
Modules are specialized to solve
particular adaptive problems: For
example, mate selection, language,
social co-operation.
Human behavior is acquired during the
lifetime of the individual.
Modules are inherited from ancestors
who adapted to the EEA. The individual's
internal and external environment plays a
role in the expression of modules. Rather
like setting the preferences for a
computer program.
Culture determines what is learnt.
Culture is a product of specialized
modules. For example a page of text is
the product of a word processing
program.
We can arrive at a conscious decision
about the best solution to many
everyday problems.
Many of the reasons for our behavior are
unconscious
Problems Faced by Ancestral
Humans
• Problems of Survival: Getting the organism to
a point where it is capable of reproducing.
• Problems of Mating: Selecting, attracting and
retaining a mate long enough to reproduce.
• Problems of Parenting: Helping offspring
survive long enough that they are capable of
reproducing.
• Problems of aiding genetic relatives: Tasks
relevant to assisting non-descendent kin.
Human Survival Problems
• Food selection: The most general problem in
food selection is how to obtain adequate
amounts of calories and essential vitamins.
– However, we must also avoid poisoning ourselves.
• Plants have adapted toxins that help reduce
the odds that the plant will be eaten.
• Hypothesis: humans have evolved taste
preferences to avoid toxic materials.
• How do we test this?
Taste Aversions
• Evidence suggests that the materials that
smell and taste bad to humans are also the
materials that are potentially harmful to us.
– Broccoli and brussel sprouts contain
allylisothiocynate which can be toxic in children
(Nesse & Williams 1994)
• We have adaptive mechanisms for removing
harmful materials from our body.
– Vomiting.
Morning Sickness
• The percentage of women who experience morning
sickness has been reported to be anywhere from 75 –
89%. However, estimates suggest that the actual %
is near 100.
• Hypothesis: Morning sickness is an adaptation to
avoid consuming teratogens during the critical period
in the development of the fetus.
– Evidence: The foods that pregnant women report to be most
nauseating are correlated with high levels of toxins.
– Evidence: Morning sickness occurs at the same time that the
fetus is most vulnerable to toxins.
– Evidence: Morning sickness decrease around the same time
that the period critical for fetal development has passed.
Morning Sickness
• Remember, an adaptation must confer an
increase in fitness.
• Hypothesis: Women who do not experience
morning sickness will be more likely to have
problems during their pregnancy.
– Evidence: Women who do not experience M.S.
are 3 times more likely to experience a
spontaneous abortion (Profet, 1992)
Stimulus Expectant vs.
Stimulus Dependent
• Expectant
–
–
–
–
–
Walking
Language (1st)
Attachment
Love
Sex
• Dependent
–
–
–
–
–
Driving
Reading
Chess
Algebra
Language (2nd)
Prepared Learning
• In the 60’s John Garcia conducted a series of
studies on taste aversion in rats.
– Rats could quickly associate a novel taste with
sickness even if the sickness did not occur until
hours after experiencing the novel taste.
– Rats could not associate a novel color or texture
with sickness without repeated exposure.
• Harlow (1971) experiments with infant
monkeys.
– Infant monkeys prefer soft terry cloth surrogate
mothers to wire mesh mothers even if only the
wire mesh mothers feed the infants.
Prepared Learning
• There appears to be adaptive predispositions
to quickly acquire specific associations.
• That is, learning is biologically constrained.
• Organisms can quickly form associations
between stimuli and responses that are (or
were) relevant to their survival in normal
situations.
Human Fears
• Fear can be viewed as an adaptive
response to avoid situations that may
lead to injury or death.
• Have humans evolved adaptive fear
responses to specific stimuli? Or do
humans learn fear responses through
conditioning?
Common Fears and Phobias
• The majority of reported fears and phobias
involve:
–
–
–
–
Spatial stimuli: heights, confined spaces
Specific animals: snakes, bats, spiders
The dark
Public speaking
• There have been very few reported phobias
of electricity, cars, busses, power tools, wood
stoves, lawn mowers, mountain bikes, X-ray
machines, cell phones etc…
Prepared Fears
• Mineka (1983) observed that rhesus monkeys
raised in captivity did not show a fear
response when confronted with a snake.
• If these monkeys were shown videos of other
monkeys displaying fear in the presence of a
snake the subject monkeys quickly acquired
the same fear response. (same for crocodile)
• If captive raised monkeys were shown a
video of monkeys displaying fear in the
presence of a pot of flowers the subject
monkeys did not acquire a fear response to
flower pots. (same for rabbit)
Prepared Fears in Humans
• Human subjects more quickly form
associations between images of snakes or
spiders and a mild electric shock than
between images of electrical cords or
mushrooms and a mild electric shock.
• They also report that the shocks that occur
after images of snakes and spiders are more
painful!
The Case of Language
Skinner:
Operant learning
(empiricist)
Vs.
Chomsky:
Inborn Universal Grammar
(nativist)
The Case of Language
•Skinner – like rats
–Associate, imitate, repeat
–Trial and error learning
–Taught how to speak
•Chomsky
–Hard-wired for language acquisition
–Endowed with core rules and ability to
apply those rules
The Case of Language
•children do learn language used in
their environment, but:
•rate at which this happens can’t be
explained by learning principles
•children generate all sorts of novel
sentences
•rarely exposed to correctly formed
language
•adults are inconsistent
The Case of Language
•Children apply logical
grammatical rules
–Overgeneralizations
•General rules for plural forms of
nouns, past tense of verbs
•Impose regular forms on irregular
nouns/verbs
The Case of Language
There are 3,628,000 ways to
arrange this sentence’s 10 words.
•Language (even sign) just happens.
•Our 5000 languages are dialects of the
universal grammar pre-wired in human
brains.
Language Acquisition Device
•LA is like a box - LAD - in which
grammar switches are thrown as
children experience their language.
–English-speaking children learn to put
object last (“She ate an apple.”)
–Japanese-speaking children learn to
put object before verb (“She an apple
ate.”)
Transformational Grammar
•Chomsky
–deep structure - meaning
–surface structure - exact wording
–sentences may differ in SS but
convey the same DS, or vice
versa
Transformational Grammar
“John kicked the ball.”
“The ball was kicked by John.”
“Visiting relatives can be a nuisance.”
Mind as Swiss Army Knife
• The human mind is
the Swiss Army
Knife that has all the
tools.
• Different species
have different sets
of tools.