Transcript Partners - UCSB Economics

Some Evolutionary Economics of
Family Partnerships
Ted Bergstrom, UCSB
An Arboreal Allegory
• Alice and Bob live on fruit and berries.
• They get cold at night.
• Alice is a skilled fire-builder. Bob is not.
Primitive cooperation
• Alice divides her time between gathering
food and building fire.
• Bob doesn’t try building fires. He spends
all of his time gathering food and he
huddles next to Alice’s
• And wishes she would build a bigger fire.
• Bob leaves some food by the fire for Alice.
• He benefits because Alice makes a bigger
fire. (income effect of food Bob leaves)
Too Little Fire
• No love or altruism is involved. Both
benefit from Bob’s gifts to Alice.
• But there is still an undersupply of fire.
• Alice accounts only for her own benefit
when deciding how much fire to build.
• A scheme where Bob pays Alice a wage
that depends on how much wood she
gathers would make both better off.
• But this requires monitoring that may not
be possible.
Case of common interests
• Suppose that all that Alice and Bob really care
about is the size of the fire.
• They want food only because it gives them
strength to do their work.
• Then Alice and Bob have dominant strategies.
• Bob eats enough to maximize the amount that
he can give to Alice.
• Alice eats enough to maximize the size of fire
that she can build.
• Both agree about what each should do.
Outcome is efficient.
How are children like fire?
• Suppose the household good is children,
who share genes of two parents.
• Evolutionary theory predicts selection for
behavior that maximizes surviving
descendants.
• Consumption of goods not an end in itself,
but an instrument for reproductive
success.
Monogamy
• Lifelong monogamous couples share
identical reproductive goal.
• Each is a perfectly motivated agent of the
other’s reproductive success.
• Common interest may be evolutionary
foundation of conjugal love.
Snakes in Eden
• In-law problem and the theory of kinselection
• Adultery
• Divorce
• Death and remarriage
The Mystery of the Demographic
Transition
• Rise of real wages and decline of net
reproduction rate.
– Western Europe 1870 to present
– Late 20th century much of Asia and Latin
America
• Puzzling to zoologists. How could natural
selection produce a creature that reduces
fertility when resources are abundant?
Economists’ Explanations
• Price effects. Children are labor intensive
goods. As wages rise, their cost rises.
– Requires price elasticity of demand for children to
exceed income elasticity
– Hard to reconcile with cross sectional data
• Technology has increased payoff to human
capital, making it more desirable to have fewer,
but better-educated children.
– But historians claim skill premiums actually fell from
18th century to present. (G. Clark)
Evolutionary explanations?
• If joint reproductive success is ultimate
motivation of couples, reproduction must
eventually rise with wages.
• No evidence that this is happening.
• Perhaps conditions are so different from
historic evolutionary environment that our
actions result of misreading cues.
Another explanation
• Humans evolved with less than complete
monogamy.
• Conflict of interest between males and
females.
• An additional child is more costly to female
than to male.
– She may die in childbirth
– Siblings suffer: They are surely hers not so
surely his.
Household Conflict
• Empirical studies show pattern of
household expenditures depends on which
household member has the earnings.
• If wife has larger share of household
income, more is spent on child health,
food, and education.
• Theory that shares of income influence
bargaining power in family decisions.
Tug of War
• If males prefer shorter birth intervals than
females, outcome will be result of a tug of
war between conflicting interests.
• Evolution might favor females who prefer
birth rates lower than their true genetic
interest and males prefer rates that are
higher than their preferred rates.
• Differences in birth rates might reflect
shifts I power between the sexes.
Power Shift Theory
A contributing factor to the demographic transition
may be that:
1) Mechanization has made the skills of females
more valuable relative to the brute strengh of
males.
2) Power and influence has shifted from males to
females.
3) With their increased influence, females have
shifted family decisions to lower fertility