ESSAY ON PARENTAL INVESTMENT

1
ESSAY ON PARENTAL INVESTMENT

• This essay is similar to the one on reproductive
  behaviour, but must only address issues which
  concern the outcome of number of offspring

2
Defining parental investment

• Any investment by a parent which increases the
  offsprings survival at the expense of the
  parents ability to invest in other offspring
• TRIVERS proposed the Parental Investment Theory
• Female investment is far greater than males.
  Female gametes are less numerous. Females can
  only have a limited number of offspring, males
  can have an unlimited number

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PARENTAL INVESTMENT THEORY

• This can be linked to sexual selection and mating
  behaviour
• Males gain from polygamy
• Females gain from monogamy.
• What does this mean in terms of number of
  offspring produced?

4
EVALUATION

• Resources and mating success in western societies
  is lowest amongst wealthier people.
• This could be because of contraception, wealthier
  males can have sex more frequently without
  incurring a cost.

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COST OF CHILDBIRTH

• As brain size increased due to adaptive
  pressures, childbirth became more difficult.
• To compensate, humans are born prematurely.
• This extends the period of childcare.
• So cost to human mothers is very high

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EVALUATION

• High maternal investment led to females choosing
  males who were good providers
• Females also wanted to ensure that they had good
  quality offspring, so efforts are not wasted.
• BAKER AND BELL supported this by discovering
  that misattributed fatherhood is 9, because
  females may sneak copulate

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MALE INVESTMENT

• Males devote much time and effort at the
  courtship and mating stage.
• They are under pressure to protect themselves
  from cuckoldry if they stay to rear their young
• Evidence for this comes from sexual jealousy.
  Females are more likely to suffer from emotional
  jealousy. Explain this

8
EVALUATION

• BUSS found that males value chastity more than
  women in 62 of cultures
• BUSS also found that males value chastity more
  than women do.
• Females are more concerned with emotional
  fidelity, because they need the man to stay
  around to help with the rearing of the offspring

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PATERNAL INVESTMENT

• This is more variable than maternal investment.
• If a man suspects a child is not his, i.e. low
  paternal confidence, he is less likely to invest
  in his offspring
• HOWEVER, joint parental investment is desirable
  in humans because parental care is extended and
  it increases the chances of the offsprings
  survival.
• This could explain why males also are choosy in
  terms of female attractiveness. They also gain
  from restricting their reproductive opportunities.

10
EVALUATIONS

• Evolutionary theory can only provide partial
  explanations of parental investment
• Cultural factors also play a part in parental
  investment patterns
• Evolutionary theory can be accused of alpha bias,
  i.e. exaggerating sex differences in parental
  investment
• Evolutionary theory is retrospective and so we
  cannot rely on empirical evidence