Individuals gain an immediate common advantage from associating, even if they're not related

For all individuals, B>C

They cooperate for mutual gain

Cooperate (R) will NEVER be ESS

Defect (P) is ESS

Tit for Tat can be ESS*

From player A's perspective what is the outcome...

1) If B cooperates and

1a) A cooperates

1b) A defects

2) If B defects and

2a) A cooperates

2b) A defects

1a) R=reward= 3

1b) T=temptation to defect=5

2a)S=suckered=0

2b) P=punishment=1

Tit for Tat (TFT) :

1) Rules

2) Compared to prisoner's dilemma

3) ESS condition

1) Cooperate on first move, then do what your opponent does

2) TFT is both retaliatory and forgiving (p.d. has no chance to be either)

3) TFT is ESS ONLY if high probability that two players will meet again

1)Benefit_R>Cost_D

2) Time b/t giving and receiving aid

3) Opportunity for reciprocity (will meet again)

4) Can recognize and remember one another (and remember/detect cheaters!!)

Reciprocal altruism of regurgitation evolved b/c benefit to starving recipient>cost to donor

(if fed bat gives 5% of body weight to hungry bat, loss of 5% decreases time until starvation from a very high number to only a few hours less, while the hungry bat gains many hours)

Cheaters identified and chastized by group

Closely associated animals (mostly kin, but not always)

All regurgitation between non-kin occurs between frequent roost-mates (opportunity to meet again)

Regurgitation is of high benefit to recipient and low cost to donor

When separate groups of bats put together, bats from different groups won't feed each other (don't know cheaters are being avoided, but know that strangers are)

1) Costs/benefits may be asymmetrical for different individuals (e.g., in grp of male baboons, if 4th ranking male helps 2nd ranking male 6x more than vice versa, this could be a symmetrical exchange)

2) Reciprocity may not always occur in same behavioral "currency" (e.g., I groom you, you help defend me in a fight)

3) Cooperation tends to occur in long term partners, so one individual exchange is of relatively low value

4) If friend doesn't seem to reciprocate symetrically, may not be worth ruining friendship if you have enough other friends

Cooperation:

1) Under what conditions does it occur?

2) What is it characterized by?

3) Is memory/ effort to interact/avoid a factor?

1) Occurs primarily among individuals who interact repeatedly (usually kin)

2) Emerges as a system of low-cost exchange of altruistic acts over extended periods of time

3) Appears not to be contingent on memory of specific events; Cheaters are not avoided, cooperators are not sought out; Participants appear to be insensitive to inequitable returns

Cooperation/ social tolerance:

- Two ropes to pull and recieve food

- If ropes close, animals can do it alone, but if far, arm span not large enough, need help

- Not sensitive to sharing/sustaining cooperation

- If only one bowl of food, the dominant individual will take all of the food, so subordinate will eventually stop helping

Reciprocal Altruism:

- Can pull one lever that delivers food to self, can pull another lever that delivers food to self AND to companion in next cage

- Predicted that when individual in second cage, would pull lever 2 to help friend and hopefully gain reciprocity

- Disproven--> it was about chance; in 50% of trials, next door cage is empty, but no difference between which lever selected whether second chimp is there or not

**Helping others selflessly has not been selected for; experimental data is limited in analyzing reciprocal altruism

Often experience higher reproductive success (especially in females), so cooperation should be selected for

(female baboons experience less stress and higher offspring survival/longevity)