COMPARATIVE PSYCHOLOGY Evolutionary explanations of human behaviour

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COMPARATIVE PSYCHOLOGYEvolutionary explanations
of human behaviour

• Four important points to recognize in relation to
  evolution
• Evolution is a fact. Living species have changed
  or evolved over time.
• Darwins theory of evolution is an attempt to
  explain the
• forces that cause such change.
• Natural selection is the basic process that
  drives evolution.
• Any trait that enhances reproduction will be
  naturally selected.

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COMPARATIVE PSYCHOLOGYEvolutionary explanations
of human behaviour

• HUMAN REPRODUCTIVE BEHAVIOUR

• THE NATURE OF SEXUAL SELECTION

• An important adaptive problem for both sexes is
• the selection of a suitable mate.
• Certain characteristics lead to lower
  reproductive
• success therefore are not selected.
• Low in re-productive capacity (e.g. older) is
  one
• characteristic.
  
• Cont

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COMPARATIVE PSYCHOLOGYEvolutionary explanations
of human behaviour

• HUMAN REPRODUCTIVE BEHAVIOUR

• THE NATURE OF SEXUAL SELECTION

• Males and females face different adaptive
• problems when selecting a mate.
• Since women have to make a greater investment
• in their offspring, through gestation and infant
  care,
• they are more choosy whom they will mate with.
• Males have to compete with each other
• (intrasexual competition) to be chosen.
  

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COMPARATIVE PSYCHOLOGYEvolutionary explanations
of human behaviour

• HUMAN REPRODUCTIVE BEHAVIOUR

• FORMS OF SEXUAL SELECTION

• Physical and behavioural indicators reveal
  traits that could
• be passed on to offspring (good genes) and
  information
• about the chances of the mate surviving to
  protect and support
• the offspring (selection for good parents).
• Indicators tend to be Conditional dependent -
  healthier
• individuals take better care and make better use
  of the indicators
• they have (better groomed and better displayed).
• Cont

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COMPARATIVE PSYCHOLOGYEvolutionary explanations
of human behaviour

• HUMAN REPRODUCTIVE BEHAVIOUR

• FORMS OF SEXUAL SELECTION

• Human beings are pre programmed to attend to
  displays
• of these important indicators, which in turn
  increases their
• Willingness to mate.
• Male humans have medium sized testicles by
  primate
• standards, suggesting that the norm for ancestral
  males
• was to be mildly competitive, so females must
  have had
• multiple partners (Bakers and Bellis, 1995).

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COMPARATIVE PSYCHOLOGYEvolutionary explanations
of human behaviour

• HUMAN REPRODUCTIVE BEHAVIOUR

• CONSEQUENCES OF SEXUAL SELECTION

• Dimorphism physical differences between sexes.
• Polygynous mating system one male and many
  females.
• The moderate size difference between human males
  and human female suggest that our species evolved
  under a polygynous mating system, with more
  intense sexual competition between
• males than females.
• Cont

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COMPARATIVE PSYCHOLOGYEvolutionary explanations
of human behaviour

• HUMAN REPRODUCTIVE BEHAVIOUR

• CONSEQUENCES OF SEXUAL SELECTION

• Females with (child like) facial features, such
  as large eyes and small noses are universally
  considered more attractive (Perrett et al.,
  1994), as are males faces with testosterone
  influenced features such as strong jaws and
  larger noses (Thornhill and Gangestad, 1993)
• Neophilia (the love of novelty) influences mate
  choice in many species. Creative behavioural
  courtship displays such as jokes, dance, music
  and art (Muller, 1998).

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COMPARATIVE PSYCHOLOGYEvolutionary explanations
of human behaviour

• PARENTAL INVESTMENT

• SEX DIFFERENCES

• Sexual selection occurs as a result of the
  different levels of parental investment between
  males and females, as well as between different
  individual men and females.
• In humans, it is the female who biologically
  invests more than the male.

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COMPARATIVE PSYCHOLOGYEvolutionary explanations
of human behaviour

• PARENTAL INVESTMENT

• SEX DIFFERENCES

• Why do human females invest more than males?
• Anisogamy females invest in producing
  relatively few, large, long lasting and energy
  rich gametes (ovum), while men produce many short
  lived and rapidly renewable gametes (sperm).
• Gestation and lactation females provide more
  resources by developing the zygote internally for
  nine months (gestation) and producing milk for
  offspring nutrition (lactation).
  

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COMPARATIVE PSYCHOLOGYEvolutionary explanations
of human behaviour

• PARENTAL INVESTMENT

• SEX DIFFERENCES

• Why do human females invest more than males?
• Parental certainty because of anisogamy and
  internal conception, the females always knows the
  offspring is hers unlike males (parental
  guarantee is not certain).
• Commitment to resources because of the
  previous factors and the helpless nature of
  babies, females are likely to continue care for
  the baby due to the already significant
  investment put in by the mother.
  

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COMPARATIVE PSYCHOLOGYEvolutionary explanations
of human behaviour

• PARENTAL INVESTMENT

• SEX DIFFERENCES

• Male investment!
• Male investment after conception is more
  uncertain due to lack of parental guarantee.

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COMPARATIVE PSYCHOLOGYEvolutionary explanations
of human behaviour

• PARENTAL INVESTMENT

• SEX DIFFERENCES

• Male investment!
• Further male investment depends on part 1
• 1 the number of females available.
• 2 a low female to male ratio.
• 3 a high degree of competition from other
  males.
• 4 a low appeal to other females (mate choice).
• All the above points will increase the investment
  in offspring.

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COMPARATIVE PSYCHOLOGYEvolutionary explanations
of human behaviour

• PARENTAL INVESTMENT

• SEX DIFFERENCES

• Male investment!
• Further male investment depends on part 2
• 1 The likelihood of infant survival.
• 2 Harsh climate.
• 3 Many predators.
• 4 Lack of food and social support.
• The helpless infants are less likely to survive
  with only the mothers care.