Evolution and Human Behavior

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Evolution and Human Behavior

• Sociobiology The New Synthesis (1975) by E. O.
  Wilson
• A total of 26 chapters, the last one on human
  beings
• Controversy followed Culture vs Biology

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Edward O. Wilson
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Misunderstandings About Sociobiology

• Human beings are not concerned about inclusive
  fitness We often dont know what motivates us,
  like food preferences and mate preferences
• Much of human behavior is not adaptive The
  concept of the Environment of Evolutionary
  Adaptation (EEA)
• Sociobiology is a justification of racism and
  elitism Confuse what is with what should be

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Evolutionary Psychology

• Assume the mind is modular made up of
  specialized circuits
• Designed to solve re-occurring problems from the
  EEA
• Domain specific
• Analogy to a Swiss Army knife

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Wason Selection Task

• You are the new file clerk at the local high
  school. You must verify that documents conform to
  a certain rule. The rule is
• If a person has a D rating, then his documents
  must be marked code 3.
• Which of the following do you need to see
  additional information? 1. D 2. F 3. 3
  4. 7

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Wason Selection Task

• You are the bouncer at a bar. You need to be
  sure that the law is not being broken. If a
  person is drinking beer, the he must be over 21
  years old. Which of the following do you need to
  see additional information?
• 1. drinking beer 2. drinking coke 3. 25 years
  old 4. 16 years old

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Logical Structure is the same

• If P then Q.
• Logically the rule for testing the truth involves
  P and not-Q.
• The content makes it easy for the beer drinking
  example, much harder for the file clerk example
• The brain is specialized to detect cheaters in
  social interactions.

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Arbitrary Culture Theory

• In opposition to evolutionary explanations of
  human behavior
• Claims that most behavior is a reflection of
  traditions and unique customs of a particular
  people
• Example High rates of adoption in the islands in
  the central Pacific ocean

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Evolutionary Explanation of Adoption

• Adoption should be frequent when adopted children
  are related to the adopting parents

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Proximate Mechanisms for Adoption

• Parental instincts are aroused for childless
  couples
• Inability to have children is most frequently
  given reason for seeking adoption
• In the EEA infertile women would likely be living
  with close relatives making adoption adaptive
• Many childless women and couple treat pets
  (usually dogs) like children

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What Do We Want in a Mate?

• From the standpoint of fitness, we want
  successful offspring
• Males want a female who will become pregnant and
  have a healthy baby
• Women want men who will help raise the offspring

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Male Mate Preferences

• Youth Females maximum fecundity is at about 26
  years old
• Waste-to-hip ratio of .7 Also an honest marker
  of fertility and health
• Narrow waist, large breasts Also correlated with
  fertility

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Roger Rabbits Wife
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WHR Predicts Cognitive Ability in Offspring
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Mate Preferences and Ovulatory Cycle

• Humans females are supposed to be Concealed
  Ovulaters giving no sign of their fertile period
• Tee shirt studies show that males prefer the
  smell of ovulating women over non-ovulating
• Males rate faces of ovulating women as being
  more attractive

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More on Ovulation Cycle

• Women show more skin and touch men more during
  their fertile period
• Women prefer a masculinized male face during
  their fertile period and non-masculinized
  otherwise
• Paradoxically, women rate their own
  attractiveness lower during their fertile period

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Female Mate Preferences

• Men who have resources Professional, good job,
  educated
• Men who are older
• Men who are high in status
• Men who are athletic
• Men who have masculine faces (testosterone
  correlated)

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Masculine Faces

• Testosterone levels during development correlate
  with masculinized face
• High testosterone may also signal a strong immune
  system
• Testosterone has a pleitropic effect High levels
  early in life may shorten life span
• Increasing masculinity from left to right in next
  slide

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Income and Earning Power

• Data from surveys show females rate earning
  potential much higher than males, across 37
  countries (David Buss)
• Data from Man seeking woman and Woman seeking
  man ads also confirm the difference

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Mate Preferences for Both Sexes

• Kind and Considerate
• Good sense of humor
• Symmetry of face and body A marker of good
  developmental homeostasis

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Conditional Mate Preferences

• Self rated attractiveness is positively
  correlated with preference for attractiveness in
  a mate

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Conditional Preferences

• Minimum acceptable intelligence for different
  levels of involvement (50 means at the middle of
  the intelligence scale for the population

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Clark and Hatfield Study

• Had an attractive male or female experimenter
  approach a member of the opposite sex
• Experimenter ask the stranger, would you like to
  go out with me?, or would you like to come to my
  apartment tonight? Or would you sleep with me
  tonight?
• Females 50, 10, 0 said yes
• Males 50, 60, 65 said yes

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Number of Partners

• Males desire more partners in their lifetime than
  do females
• Males would engage in sex sooner in the
  relationship than females

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Jealousy

• Males are concerned with paternity of offspring
• Females are concerned with help raising offspring
• Threats to these characteristics give rise to
  jealousybecoming upset

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Which is more upsetting?

• Imagine yourself in a committed relationship and
  your partner becomes involved with another
  person. Which is more upsetting?
• You partner has a passionate sexual relationship
  with that person
• Your partner has formed a deep emotional bond
  with that person

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Which is more upsetting?

• Imagine the same committed relationship, but now
  your partner becomes involved with a person of
  the same sex as your partner. Which is more
  upsetting?
• You partner has a passionate sexual relationship
  with that person
• Your partner has formed a deep emotional bond
  with that person

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Results

• Heterosexual relationship Males say sex 60,
  females say sex 30
• Homosexual relationship Males say sex 50,
  females say sex 80
• Cross-cultural research CroatiaMales say sex
  50, females say sex 85 for hetero, and males
  say sex 50, females say sex 65 for homosex.

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Sex Differences in Spatial Abilities

• Division of labor Hunters and gatherers
• To be a good hunter must be able to keep track of
  where the prey is, where home is and how to get
  there Spatial rotation task.
• To be a good gatherer must remember where food
  was located Plants dont move around. Spatial
  memory task

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Human Conditional Mating Strategies

• Recall conditional strategy of the scorpionfly
  guard insect, produce saliva, forced copulation
• Is human rape a conditional mating strategy? Or
  is it males way for controlling females by fear?

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Characteristics of Rape

• Females are more likely to become pregnant by
  rape than by consensual sex
• If rape is an adaptation, then most fertile women
  should be most often raped
• If rape is male intimidation, then it should be
  most frequent in women who are in powerful
  positions, and should be comparable to murder

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Rape as a maladaptive side effect

• Males motivation for many sexual partners and
  quick sexual arousal lead to over-expression of
  sexual behavior
• Predicts that rapists should have more consensual
  sex than average, which is supported by some data
• Final explanation of why rape occurs is not done

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Parental Care

• Certainty of parenthood affects amount of
  parental (grand parent) investment
• How much support have you received from your
  grandparents?
• Mothers mother has greatest certainty of
  parenthood, fathers father the least certainty,
  and fathers mother and mothers farther are
  intermediate

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Students ranking each grandparent as most
invested
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Parental Resource Allocation

• Males must often compete for limited number of
  females
• Bridewealth is male giving resources to females
  family
• Dowry is female giving resources to males family
• Bridewealth is much more common, particularly in
  polygynous cultures

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Inheritance

• Sons receive more inheritance from parents that
  daughters, particularly in polygynous cultures
• In monogamous cultures, sons are favored 58 of
  the time
• In polygynous cultures, sons are favored 80 to
  97 of the time

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A Sons Inheritance

• Increased wealth increases the proportion of
  inheritance given to sons
• High levels of wealth increase a males chances of
  successful reproduction
• Data from Canada

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Biological vs. Non-Biological Parents

• Step children are usually not given as much
  parental investment as biological children
• Giving a child money to help attend college

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Stepchildren

• Step children are more at risk for child abuse
  than biological children
• Daly and Wilson data show that step child is 100
  times more likely to be killed than biological
  child
• Child abused is also higher in stepchildren,
  especially young ones

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Stone-age Mind in a Modern Society

• Many problems with todays world may have been
  adaptations that were successful in our
  evolutionary past
• Eating sweet and calorically rich foodsobesity
• Opportunistically using resources
  deforestation, over-farming, over-fishing
• Producing tools and artifacts quickly and
  efficiently pollution

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• Cooperation in hunting and other tasks
  in-groupout-group mentality
• My group is good, the other groups I meet are not
• Ability to acquire information from experience
  bad information is as easy to acquire as good.
• Chimps hunt in groups and return home after the
  hunt

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The Future

• E. O. Wilson claimed in his book, Sociobiology
  The New Synthesis in 1975 that evolutionary
  theory would transform the social and behavioral
  sciences
• Was he right?