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Why Are Humans
Altruistic?
Joel H. Benington, Ph.D.
Department of Biology
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What is Biological Altruism?
Ultimate altruism: An action that, on average,
decreases the lifetime direct fitness of an actor and
benefits one or more recipients Proximate altruism: An action
that, on average,
imposes costs on an actor and benefits one or
more recipients
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Worker bees reduce lifetime direct fitness
by not reproducing
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Kin Altruism
If cost to self is less than
(benefit to others) x (degree of relatedness)
then behavior increases inclusive fitness allele(s) causing
behavior become more
common in population
is/are selected for
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Reciprocal altruism
Sentries
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Reciprocal altruism
Alarmcalls
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Reciprocal altruism
Grooming
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Studying Altruism in Humans
Prisoners Dilemma games
Public Goods games
Ultimatum game
Players are anonymous in all games
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Public Goods Games
Like prisoners dilemma but 3+ players
Players keep stake or contribute to common pool
Each player gets half of what is in common pool All do better if
all cooperate
but cooperation decreases over time
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Public Goods Games
with Punishment After each round, players can punish
cheaters
$1 spent costs cheater $3 (altruistic punishment)
Humans do proportionally punish cheaters
Cooperation is maintained if there is punishment
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Ultimatum Game
Two players
One chooses how to divide a pot of money
Other either accepts or rejects offer If rejected, neither
player gets anything
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Ultimatum Game
with Third-Party Punishment Two players, one divides pot, as
before
Third player can reward/punish first
E.g., spend one dollar to cost cheapskate three
Rewards/punishments happen even in one-round
games
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Humans are notRational
Maximizers of Personal Utility Rejections in one-round ultimatum
game
Third-party rewards/punishments in one-round
ultimatum game
Egalitarian preference (by age 8 in children)
Other-regarding preferences (for and against)
Homo economicus has its limits
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Limitations of Games
Other players are anonymous abstractions
Only information is prior behavior
Other players neither kin nor in social group No lasting
reputational consequences
Deck stacked against altruism/cooperation
Yet it still happens!
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How Did Humans Get This
Way?
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Our Nearest Relations
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How Chimpanzees
Resemble Humans Highly intelligent, highly social
Kin altruism, reciprocal altruism
Food sharing
Cooperative hunting and defense of territory
Hierarchical behavior, with sophisticated
political calculations
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in Friedsam
Library
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Hypothesis 1
Increasing intelligence increasing instability in
dominance hierarchy (leader churning)
Systematic coalitions of underlings undermine leader(reverse
dominance hierarchy)
Schneider: All men seek to rule, but if they cannot
rule they prefer to remain equal.
Cultural evolution at first, followed by selection forgenetic
dispositions to fairness and equality
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Mental State Attribution
Idea that other people have experiences like yours
Develops in childhood
Aware of intentions by age 2 Aware of emotions by age 3
Aware of beliefs by age 4
Chimpanzees aware ofintentions and emotions
but not beliefs; other primates aware of even less
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How Altruistic Are Humans?
Kin altruism
Reciprocal altruism
Strong reciprocation (with reward/punishment) Egalitarian
(obsession with fairness)
Sincere psychological altruism
Limits to altruism: also quite self-regarding
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[email protected]
