RECIPROCAL ALTRUISM
a) First
proposed to explain cooperation among non-kin
b) Trivers
(1971) credited with first explicit dialogue
I. Definition: Pay cost C today (confer benefit
B to recipient today), receive benefit B in the future from recipent (who pays
cost C in the future) (cf. Sahlins
reciprocity) overhead a
c) Problem
of reciprocal altruism (RA) is that expected return benefits are usually
delayed, which provides an opportunity for cheating, shirking, defecting.
ex: If you help me
today, why should I bother helping you in the future?
brood parasitism
II. Theoretical
modeling
The prisoners dilemma
and the need for repeated interaction – overhead 1, 2
biologist question:
how can you get cooperation from a null state of defection?
Axelrod’s prisoner’s
dilemma tournament overhead 3
What conditions foster RA (TFT)?
1) good
memory for score-keeping – punish defectors, reward cooperators
2) “shadow
of the future” – relatively long-term interactions with partners
- perhaps limits the kinds of species
where we see evidence for RA
Problem:
1) How
to get TFT stable when there are too many defectors?
[kinship, assortative
grouping patterns]
1) vampire
bats – blood sharing – overhead 4
2) impala
– allogrooming – overhead 5
3) predator
inspection in sticklebacks and guppies
IV. Examples of RA in humans
1) Ye’kwana
garden labor exchange
2) Ache
food sharing, other hunter-gatherers
a) cost
of food given away; expect sharing when costs low, benefits high
b) variance
in acquisition for game vs plant foods – sharing as a risk
reduction strategy,
40% chance of coming back to camp
empty-handed, Hadza – 97% for big game;
sharing benefits greatest for
asynchronously acquired, medium-large packages;
short-term vs. long-term risk – sickness,
illness, day-to-day variation, dependency load
c) but
is sharing generalized or contingent?
context-dependent nature of sharing - forest vs. settlement among Ache,
Yora – overheads 8, 9, 10, 11
d) are
there non-food benefits to sharing – mating and offspring survivorship,
prestige (value?)
e) tolerated
scrounging? are poor hunters lazy, have
no ability, or what?
- diminishing returns to consumption
Do kin make good reciprocity partners?
Do we really defect in one-shot situations and
only cooperate when there exist the potential for long-term gains? experimental economics approach.
I.
Ultimatum Game - overheads 12, 13
II. Public
Goods Game - overheads 14, 15,
16
Are people strictly TFTers or do they have an
evolved pro-social psychology?
e.g. Why do people tip in restaurants that
they’ll never return to?