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9.916Altruism and Cooperation

Today’s Lecture

I give everyone $10 Anonymous pairs Chance to send $0-$10 Anything you send, x3 How much do you send?

Puzzle of altruism: How could it evolve? free-riders should out-compete altruists

“the central theoretical problem of sociobiology”

Puzzles of human altruism: Why is human behavior cooperative / altruistic?

(a) developmental origins: genetic or learned? (b) how maintained in practice? (c) what proximal mechanisms?

Altruism & Cooperation

Coordination: Nash equilibrium = cooperate or defect

joint effort maximum collective & individual payoff no/less payoff for defection

Cooperation: Nash equilibrium = defect

maximum collective/other’s payoff joint effort higher individual payoff for defection

Altruism: Nash equilibrium = defect

joint effort increase other’s payoffcost to individual

Altruism Games What makes a “game”?

Each P’s payoff depends on the actions of other Ps

What makes an “altruism game”?

Nash equilibrium is anti-social Human behaviour is pro-social - give minimum - give more than minimum - accept minimum - refuse minimum - don’t punish - punish

But not perfectly!

Often don’t achieve: - equal split - maximum collective payoff

Altruism in 2 Player Games

P1 $10 P2Dictator (1) ?

altruism / fairness



P1 $10 P2Ultimatum (1) ? (2) Accept / Reject

altruism / fairness anticipated rejection

fairness 2p punishment



x3P1 $10 P2Trust (1) ? (2) P2 ? P1

trustingness trustworthiness fairness




x3P1 $10 P2Trust (1) ? (2) P2 ? P1

x3P1 $10 P2Gift (1) ?

altruism / fairness




x3P1 $10 P2Trust (1) ? (2) P2 ? P1

x3P1 $10 P2Gift (1) ?

x3P1 $10 P2PD (1) ?

x3P2 $10 P1(2) ?

cooperation


Core Dilemma of Cooperation

Standard Solution: Positive assortment

Cooperators benefit other cooperators

Henrich & Henrich 2007

Natural selection for cooperation

βb > c Probablity of

benefiting cooperator

Benefit of receiving cooperation Cost to

cooperator

r - probability of sharing cooperation by descent ω - probability of continuing interaction ϕ - probablity of accurate reputation

favours cooperating: - closely related

- long future - low noise

- quantifiable exchange








Note 1: Simulations - Axelrod’s (1980) computer tournaments - repeated prisoner’s dilemma - round 1: 14 entries - round 2: 62 entries - round 3: ecological simulation - winner: tit-for-tat

cooperates first, then tit-for-tat

Example 1: cleaner fish









cooperates first, then tit-for-tat Example 2: Cooperation in the trenches

Axelrod 1984 / 2006

Core Dilemma of Cooperation Example 2: Cooperation in the trenches

Small battallions, stationary trenches -> Long futures, quantifiable exchanges

Step 1: Recognise common interest in silence

Step 2: Be provokable; show that the silence is deliberate

Step 3: Damping? Step 4: Passing info along

Axelrod 1984 / 2006









cooperates first, then tit-for-tat

Axelrod 1984 / 2006

Special case? - dyadic

- long future - no noise






Note 2:

Natural selection ≠ Genes Reliable transmission, fitness difference Individual learning Social learning




Entomological assumptions:

Behaviour determined by genes Transmission by genes Invasion by reproductive success

Lehnmann 2008

+ Behavioural plasticity





Standard games: - no kinship - no future - no reputation

“misfiring” mechanisms?

Note 3:




Who would you ask for a high cost

favour? Overestimate kin? Overestimate future? Feel observed?

e.g. by the experimenter

Creating Cooperation

Internal mechanisms:

- induce reciprocal cooperation Cooperate pre-emptively - avoid punishment

- create & protect reputation Cooperate when visible

Cooperate responsively - motivated to reciprocate Cooperate conditionally - strong reciprocity norm Cooperate when needed - inequity aversion / empathy

Cooperate unconditionally - prosociality: motivated to help, no expectation of punishment or reward


Transmission: Genetic? Cultural?

Look for: - different bw children & chimps - early emerging - culturally universal

Look for: - similar bw children & chimps - late emerging - culturally variable

Internal mechanisms:

- induce reciprocal cooperation - avoid punishment - create & protect reputation

- motivated to reciprocate - strong reciprocity norm - inequity aversion / empathy

- prosociality: motivated to help, no expectation of punishment or reward

Prosociality Chimps coordinate for goals:

Depends on history with partner:

Melis et al 2006

Courtesy Elsevier, Inc., http://www.sciencedirect.com. Used with permission.

Food

pla

tform

Adjacent room

Test room

Adjacent room

Door & Key

Door &

Key

100

75

50

25

0FarNear

100

80

60

40

20

0

Mea

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of t

rials

LoseWin

Session 1Session 2

ShiftStay

Figure by MIT OpenCourseWare.

http://www.sciencedirect.com

Prosociality Children coordinate for its own sake

Warneken et al 2006

Figures removed due to copyright restriction.

100

50

25

0

75

Mea

n pe

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tage

of h

its

Mea

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Double tubeRole A

High

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Leve

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No success

Toddler Chimp Toddler


Inequity aversion

No-cost Dictator “Game”:

1

0.90.80.7

0.60.5

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0.20.1

01 2 3 4 5

Session

Pull

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(mea

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0.7

0.6

0.5

0.4

0.3

0.2

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Number of 1/1 choices by partner in previous 2 trails

100

80

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03-4 5-6 7-8

Age

Perc

enta

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Prosocial game: (1, 1) versus (1, 0)1/1 1/0 or NR

Chimp Chimp Child

Vonk et al 2008, Brosnan et al 2009, Fehr et al 2009

Figures removed due to copyright restrictions.


Fehr et al 2008

Altruism / Cooperation Late emerging

But 2p requires inhibition What about 3p?

Inequity aversion

Figure removed due to copyright restriction.

- motivated to reciprocate- strong reciprocity norm- inequity aversion / empathy

Some evidence for- similar bw children & chimps- late emerging- culturally variable


Internal mechanisms: Transmission: - induce reciprocal cooperation Cultural? - avoid punishment Genetic? - create & protect reputation

Some evidence for - prosociality: motivated to help, - different bw children & chimps no expectation of punishment or - early emerging reward - culturally universal

Maintaining Altruism with Punishment

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9.916 Special Topics: Social Animals Fall 2009

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