public goods & reputation: humans recall eusocial insects: altruism inclusive fitness kin...
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Public Goods & Reputation: Humans
Recall Eusocial Insects: Altruism
• Inclusive Fitness Kin Selection
• Monogamous Queens
Multiply-Mated Queens Lower r
Kinship, Coercion & Policing
Public Goods & Reputation: Humans
Cooperation Among Non-Relatives
• Repeated Interaction
• Conditional Cooperation, Reciprocity
Sufficient for Humans?
Degree of Cooperation: Maintained?
Punish Defectors? Coerce Cooperation?
Public Goods & Reputation: Humans
Experimental Approaches: Economics & Behavioral Ecology
Public Goods GameIndirect Reciprocity
Reputation Game
1. Public Goods Game: Example
4 players
• Each player: Endowment of 20 MU
• Contributes 0 to 20 MU to Group Project/Keeps Rest
• Reward All Players: 0.4(Total Contribution)
Public Goods Game: Example
“Free Rider” Does Not Invest Takes Share of Public Good
Þ Temptation to Defect
All 4 Defect; Each Retains 20 MU
All 4 Invest Fully: Each Earns 80(0.4) = 32 MU
Metaphor: Dilemma of Social Cooperation
2. Indirect Reciprocity Game: Example
Similar to Reciprocal Altruism
Donor Gives 0 - 3 MU to Specified ReceiverPublic Donation Reputation
Donor Later Becomes Receiver:Third Individual as Donor
Reputation Earns Donation > 3 MU
If Donors Common, Stable SolutionHow Get Common?
Fehr & Gachter (2002) Nature 415:137.
Human Evolution: Dangerous Hunts, Conserve Resources, Warfare
Why Do Humans Invest in Costly Activity?
Kin Selection, ReciprocityCostly Signaling to Gain Reputation as Donor
Humans Cooperate: Non-Kin, Mixed Populations, Small Gain via Reputation
Fehr & Gachter (2002) Nature 415:137.
Punishment of Free RidersAltruistic Punishment: Has Cost
Make Cooperation Pay?
Will Individual Pay to Punish Free Rider?Entire Group Benefits
Incentive to Individual Altruist (Punish)
Fehr & Gachter (2002) Nature 415:137.
Public Goods Game with Punishment
240 Students; Groups with 4 Members
Two Treatments: Punishment & No Punishment
Individual• Choose Public Goods Investment• See All (Anonymous) Players Investment• (Choose to Punish Other Players: If Available)
Fehr & Gachter (2002) Nature 415:137.
Public Goods: Invest 0 to Endowment
Punish: 0 to 10 MU (Cost to “Altruist”)
Punished Individual: Loses 3 Cost of Punisher
Spite? Altruism toward Other InvestorsHypothesis: Free Rider Later Cooperates
Group Composition Changed Frequently
Fehr & Gachter (2002) Nature 415:137.
1. Larger Degree of Defection Incurs Larger Punishments
2. Strength of Punishment Stable Across Time
3. Frequencies?
Fehr & Gachter (2002) Nature 415:137.
1. Punishment Increases Cooperation in Public Goods Game, Compared to Game with No Punishment
2. Within Punishment Treatment, Cooperation Increases as Defectors Switch to Cooperation
3. Within No Punishment, Cooperation Declines as More Individuals Defect
Fehr & Gachter (2002) Nature 415:137.
Suggest: Free Riders (Defectors) Learn to Expect Costly Punishment and Begin to Cooperate
Suggest: Free Rider Triggers Anger, Larger Difference in Contribution Reports More Anger
Gurerk et al. (2006) Science 312:108.
Sanctioning (Punishment) “Stabilizes Human Cooperation”
Observe Lack of Sanctioning Lead to Decay of Cooperation
Stable Cooperation: Enough Individuals Willing to Pay Cost of Punishing Defectors
Identify Free-Riders and Cooperation Common: Stable
Gurerk et al. (2006) Science 312:108.
Will Individuals Prefer to Join Sanctioning Institution If Sanction-Free Institution Available?
Experiment: 84 Subjects, Game in Stages
• S0: Choose Sanctions (SI) or Sanction Free (SFI)
• S1: Contribution to Public Goods Game(Social Dilemma)
• S2: Sanctioning (If Available)
Gurerk et al. (2006) Science 312:108.
1. Subjects’ Choices (Bars)First 2 Periods, SFI PreferredAfter Period 5, SI Strongly Preferred
2. Average Contribution to Public Good(Symbols)SFI Declines to 0SI Increases to > 90%
Payoffs Approach Maximum in Sanctioning
Gurerk et al. (2006) Science 312:108.
Gurerk et al. (2006) Science 312:108
• Initial Reluctance, SI Rapidly Dominant Choice
Cooperation Becomes Common ( Stable)Cooperators, with Punishing, Earn More
• Free-Riders in SI Earn Less, Due to Punishment
• Within SFI, Cooperation Collapses
Rockenbach & Milinski (2006) Nature 444: 718.
Interaction: Indirect Reciprocity & Costly Punishment
Humans: Show Altruism, But Misuse Public Goods
Overfish Oceans, Risk Climate-Change Disaster Through Increasing Use of Fossil Fuels, …
“Tragedy of Commons”
Why Cooperate?
Rockenbach & Milinski (2006) Nature 444: 718.
Costly (“Altruistic”) Punishment of Defectors
Maintain Reputation (Indirect Reciprocity)
Assert: If Indirect Reciprocity Effective, Fewer Defectors to Punish (Cost Reduced)
Rockenbach & Milinski (2006) Nature 444: 718.
Groups of 8 Subjects Played Public Goods Game for 20 Periods
2 Treatments (Each Present/Absent)• Choose Punishment or Punishment-Free• Both Play Public Goods Game• Punishment Stage (If Applicable)• Play Indirect Reciprocity Game (If Applicable)
Rockenbach & Milinski (2006) Nature 444: 718.
Punishment AND Indirect Reciprocity(a) Largest PG Contribution, Most Cooperative(c) By Period 3, Most Common Choice
Rockenbach & Milinski (2006) Nature 444: 718.
Cost of Punishment Reduced IF Punishment Combined with Reputation Game