We evolved to compete and cooperate

• Those who cooperate can reproduce faster than who don’t,
• but there’s still competition for food and mates within a group.
• Individuals can pretend to cooperate but secretly “defect” or “free-ride.”
• Humans are sensitive to others’ deceit/intentions.

Cooperation needs attention

Who cooperates, defects, & deceives?

Sources of cooperation

direct reciprocity

via repeated exchange (bats)

indirect reciprocity

via reputation of helping high-status (your good name)

spatial selection

via social structure of helping neighbors (yeast)

kin selection

via helping family members (siblings)

multilevel/group selection

self-sacrificing members help group out-compete others (your tribe) (Nowak 2012)

Dunbar’s number

How much time do you spend gossiping?

If cooperation is so powerful, why do group projects so often suck?

Tragedy of commons (ToC)

Some circumstances make it hard to cooperate

ToC conditions

1. non-excludable (can’t limit others consumption)
2. rivalrous (their consumption affects yours)

Public goods

PG conditions

1. non-excludable (can’t limit others consumption)
2. non-rivalrous (their consumption doesn’t affect yours)

beware of free-riders!

ToC or PG??

• Boston commons
• light house
• NE fishing stock
• fire department
• clean water
• creative works (stories and music)

ToC or PG online??

Prisoner’s dilemma

Ultimatum game

I need 2 volunteers.

1. I give $10 to the Divider, who decides how to divide it with the Recipient (0-100%).
2. The Recipient decides whether the division is acceptable or if the whole deal is scratched.

3rd-party variation

I need 3 volunteers.

1. I give $10 to the Divider, who decides how to divide it with the Recipient (0-100%) .
2. I give $5 to the 3rd-party.
3. The Recipient receives whatever the Divider chose.
4. The 3rd-party can pay to penalize the Divider: for every $1 she spends, the Divider loses $2.

Did the 3rd party pay to punish?

Altruistic punishment

punish, perhaps at one’s own expense, someone else with no immediate personal gain.

60% of 3rd-parties choose to pay to punish the Decider if she shares less than half her endowment.

Nowak takes issue with the limited Fehr-Gächter game, calls their finding “costly punishment,” and in work with Dreber & Fudenberg concluded “winners don’t punish.”

Evolution of cooperation

What strategy does best when playing over multiple rounds?

• always cooperate?
• always defect?
• random/unpredictable?

Solutions to social dilemmas

• government intervention
• privatization
• Ostrom’s institutions of collective action (boundaries, rules, graduated sanctions)
• altruistic punishment: paying a small cost to punish a violator without direct benefit (e.g., telling someone who cut in line behind you to go to the end of the line)
• trust & culture

What concept could explain??

Wrap-up

1. Did we evolve to be competitive or cooperative?
2. What are two game-theory dilemmas that demonstrate their interaction?
3. What are two social dilemmas that get in the way of cooperation?

Review quiz

1. Why is the prisoner’s dilemma a dilemma?
2. What is altruistic punishment?
3. ✓ where appropriate