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Chapter 0

PSYCH 3F03 Chapter Notes - Chapter 0: Reciprocal Altruism, Exaptation, Senescence

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David Feinberg

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Costly Punishment Across Human Societies
By: Henrich et al.
For thousands of years human societies maintained cooperation in many
domains including hunting, trade, and warfare
o The scale of this cooperation is a puzzle as neither kin selection nor
reciprocity explains altruism in large groups of unrelated individuals
Reputation can support altruism in large groups but some other mechanism
is needed to explain why reciprocity should be linked to prosociality not
selfish or neutral behavior
Cooperation can evolve in situations with no reputation or repeat interaction
if cooperators also engage in costly punishment of non-cooperators
o Costly punishment exists, it is effective in sustaining cooperation and
there is a willingness by uninvolved third parties to punish in
anonymous situations
o Is suggested that societies in which costly punishment is common will
exhibit stronger norms of fairness and prosociality as punishment
keeps these norms stable
Findings revealed some consistent patterns of punishment in all populations
(diverse populations from 5 continents) but substantial variation across
populations in their willingness to punish
o Punishment correlates with altruism across populations in a manner
consistent with coevolutionary theories
Experiment 1
Ultimatum game (UG): two anonymous players are allotted a sum of real
money in a one-shot interaction
o Player 1 can offer a portion of sum to player 2 and player 2 before
hearing the amount offered by player 1 must decide whether to accept
or reject each of the possible offers
o If player 2 accepts actual offer he receives amount offered and player
1 recieves the rest
o If player 2 rejects actual offer both players receive zero
o If motivated by purely self-interest player 2 will always accept any
positive offer and player 1 should offer the smallest nonzero amount
o Player ’s willingness to reject is a measure of costly punishment
known as second-party punishment
Experiment 2
Third part punishment game: two players are allotted a sum of real money
and a third player gets one-half of this amount (of total sum of money)
o Player 1 must decide how much of the money to give to player 2 (who
makes no decision) and player 3 before hearing amount offered has to
decide whether to pay 10% of the their money to punish player 1,
causing a deduction of 30% of the money player 1 keeps
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o Player ’s punishment strategy is elicited for all possible offers by
player 1
o In a purely self-interested situation player 3 would never pay to
punish player 1 and player 1 should always offer zero to player 2
o )ndividual’s willingness to pay to punish provides a direct measure of
the person’s taste for a second type of costly punishment, third-party
Dictator game (DG)
Used as a behavioral measure of altruism not linked to kinship, reciprocity,
reputation, or the immediate threat of punishment
Same as UG except that player 2 cannot reject
Player 1 merely dictates the portions of the money received by them and
player 2
A purely self-interested individual would offer zero
Stake sum of money was  day’s wage in the local economy to guarantee
motivation and attention
Punishment Results
Both types of costly punishment showed a universal pattern, with an
increasing proportion of individuals from every society choosing t punish as
offers approach zero
There was substantial differences across populations in their overall
willingness to punish unequal offers
Ultimatum game results
For every population probability of rejection decreased as offers increase
from 0% to 50%
At the lowest offer for which punishment is costly (10% offers), 56.5% of
players rejected overall
o Magnitude of this effect varied across groups
Income-maximizing offer: offer that maximizes player ’s income given the
observed rejection probability
o IMO varied from 10% (little punishment) in eight populations to 50%
(strong punishment) in two
Minimum acceptable offer: the lowest offer between 0-50% that a player
would accept
o Used as dependent variable to see if punishment variation caused by
demographic and economic differences in populations
o 7% of variance is explained by sex, age, education, household size, and
o substantial portion cannot be explained by the above predictors
6 of 14 populations display a willingness to reject increasingly unequal UG
offers as they rise from 50% to 100%
o half of sample reject offers of 100% in two populations
o willingness to reject hyperfair offers (offers over 50%) is widespread
mild versions of this have been detected in the US and Europe
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maximum acceptable offer: highest offer above 50% a player will accept
o used as regression
o 17% of MXAO variation is between populations
o very little variation among populations can be explained by measured
differences in economic and demographic variables
Third person punishment game results
similar to those seen in the UG, with all societies showing a decreasing
frequency of punishment as offers increase to 50% as well as substantial
differences between populations
/ of player ’s were willing to pay % of their money to punish player 
for allocating zero to player 2
again differences between-populations is not explained by economic and
demographic differences
costly punishment is present across a highly diverse range of human
populations and emerges in a pattered fashion
o less-equal offers were punished more frequently
there is substantial variation among populations, with some societies
showing very little overall willingness to punish and others revealing a
willingness to punish offers that are too generous or too stingy
o suggests that the same institutional forms may function differently in
different populations
o different cultural equilibria
at the population level, this willingness to punish covaries with a behavioral
measure of altruism
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