Demographic Transition II

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Lecture 24

• Demographic Transition II

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Overview

• Psychological mechanisms do not determine
  optimum number of children, only appropriate
  times to reproduce
• Improvements in medical technology have
  drastically decreased mortality rates
• This allows for long periods of investment to pay
  off (if mortality was high, then many would die
  before investment could bring returns)
• Payoff for education increased as number of jobs
  for skilled, educated workers increased
• Parents realized increased investment needed to
  be successful, for themselves and for their
  children
• Maximization of fitness did not evolve, only a
  sensitivity to conditions that determine when it
  is beneficial to reproduce

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Shift to Below Replacement Fertility

• Payoffs to education increased
• As birth control became more effective, and
  families became smaller, payoff to women working
  in the home decreased
• Women invested more in education and expected to
  invest more in childrens education
• Men and women switch from complimentary
  investments to substitutable (equal) investments
  and divorce rates rose as parents became less
  dependent upon each other

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Shift to Below Replacement Fertility (contd)

• Men and women became more selective when looking
  for spouses to decrease possibility of divorce,
  which also postponed marriage and reproduction
• Many couples are unable to have desired number of
  children because they waited too long
• All of these factorsincreased investment in
  individuals education (postponing
  marriage/reproduction), increased selectivity for
  spouse (again postponing marriage/reproduction),
  and decrease in desired fertility to allow
  increased investment in childrens
  educationresults in below replacement fertility

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Summary and Conclusions

• As a result of human evolutionary history, human
  parents invest heavily in the embodied or human
  capital of offspring. The large human brain, the
  long period of juvenile dependence, long lifespan
  and male support of reproduction are the
  co-evolutionary result of a niche based on
  skill-intensive techniques of resource accrual.
  Parents adjust investment in offspring depending
  upon the returns to skill.
• The regulation of fertility under traditional
  conditions is based upon a co-evolved psychology
  and physiology. When all wealth is somatic, the
  hormonal system controlling ovulation and
  implantation translates income into genetic
  descendants. When some wealth is extra-somatic
  there can be a conflict between consciously
  desired fertility and the fertility output of the
  hormonal system, leading to the practice of birth
  control.
• Increased payoffs to investment in skills and
  education in the context of competitive labor
  markets interacted with increased survival rates
  to favor increased investment in own and in
  childrens embodied capital, dramatically
  lowering fertility rates and increasing the
  demand for effective birth control.

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Summary and Conclusions

• Education is an increasingly important
  determinant of wage rates, fertility behavior and
  parental investment.
• Increased investment in own and offspring
  embodied capital also leads to increased
  selectivity in choosing a marriage partner and
  the timing of reproduction.
• Delays in reproduction due to investments in
  education, on-the-job training, and selectivity
  in mating result in target fertility not being
  reached among many individuals with there being a
  mismatch between social maturity and
  physiological maturity.

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Summary and Conclusions

• Below replacement fertility may be the result of
  an increase in individuals involuntarily falling
  short of their ideal due to excessive delay and a
  decrease in those involuntarily exceeding their
  ideal due to failed birth control.
• A four-step process was employed to develop a
  theory of modern fertility 1) model the effects
  of natural selection on fertility behavior 2)
  apply it to the ecology of hunter-gatherers 3)
  specify the proximate psychological mechanisms
  that evolved to respond to ecological variation
  among hunter-gatherers 4) develop and test a
  model of how modern conditions might interact
  with those mechanisms to produce observed
  behavior.