Evolutionary Psychology

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					      Evolutionary Psychology

Modern skulls house a
  stone age mind
       Basics of Evolutionary
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
• 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
• It can be shown that humans have evolved
  physiological traits in response to adaptive
• 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
• We can see the cumulative effects of
  selective pressures when we observe human
     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
• 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
• EPM’s are not rigid instincts, they
  depend upon modulation by the
  – 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.
• 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)   Body structure (e.g. hands, kidneys, eyes) has
has evolved                                  evolved
There are several types of scientific        All science is a single coherent entity consisting of
Endeavour e.g. natural sciences (biology,    many disciplines e.g. physics, biology, psychology,
botany, zoology etc.); social sciences       sociology etc. - all characterized by adoption of the
(sociology, psychology, politics etc.)       scientific method.

Psychology is a social science. Social       Biology is a natural science. Biology is built upon the
sciences are concerned with how culture      rock of evolutionary theory. Psychology is a branch
and experience produce wide variation in     of biology.
human behavior. Therefore social sciences
do not need to consider the role of
evolution in the development of behavioral

Animal behavior is controlled by their       Animal and human behavior are biological
biology. Human behavior is determined by     phenomena that have evolved.
culture and experience. Animal behavior is   Ignorance of evolutionary theory can lead some
more appropriately studied by biologists.    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 human mind consists of specialized
the ability to learn. Essentially we are      modules that are innate and have
'empty computers' or 'blank slates' at        evolved via natural and sexual selection
birth, written on by the hand of culture      to cope with adaptive problems. Modules
and experience.                               resemble debugged computer programs
Fodor (1998) expresses this idea as           designed for a particular process e.g.
follows:                                      word processor, spreadsheet, database.
"Most cognitive scientists still work in a    Fodor (1998) writes that evolutionary
tradition of empiricism and                   psychologists view
associationism whose main tenets              "..the mind as computational system; the
haven't changed much since Locke and          mind is massively modular; a lot of
Hume. The human mind is a blank slate         mental structure, including a lot of
at birth. Experience writes on the slate,     cognitive structure, is innate; a lot of
and association extracts and                  mental structure, including a lot of
extrapolates whatever trends there are in     cognitive structure, is an evolutionary
the record that experience leaves. The        adaptation - in particular, the function of
structure of the mind is thus an image,       a creature's nervous system is to abet
made a posteriori, of the statistical         the propagation of its genome (its selfish
regularities in the world in which it finds   gene, as one says)."
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."
Human behavior is controlled by a       Modules are specialized to solve
general purpose systems which rely      particular adaptive problems: For
on imitation, general intelligence,     example, mate selection, language,
culture, reward and punishment. These   social co-operation.
systems are content-independent or

Human behavior is acquired during the   Modules are inherited from ancestors
lifetime of the individual.             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

We can arrive at a conscious decision   Many of the reasons for our behavior are
about the best solution to many         unconscious
everyday problems.
Problems Faced by Ancestral
• 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
• 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            • Dependent
  –   Walking            –   Driving
  –   Language (1st)     –   Reading
  –   Attachment         –   Chess
  –   Love               –   Algebra
  –   Sex                –   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
  – 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
           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
 Common Fears and Phobias
• The majority of reported fears and phobias
  –   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
      The Case of Language
Operant learning


Inborn Universal Grammar
     The Case of Language
•Skinner – like rats
  –Associate, imitate, repeat
  –Trial and error learning
  –Taught how to speak
  –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
    •rarely exposed to correctly formed
    •adults are inconsistent
    The Case of Language
•Children apply logical
 grammatical rules
    •General rules for plural forms of
     nouns, past tense of verbs
    •Impose regular forms on irregular
     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
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
 Transformational Grammar
 –deep structure - meaning
 –surface structure - exact wording
 –sentences may differ in SS but
 convey the same DS, or vice
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
            • Different species
              have different sets
              of tools.

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