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 Game Indirect 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 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 MU to Specified Receiver Public Donation Reputation Donor Later Becomes Receiver: Third Individual as Donor Reputation Earns Donation > 3 MU If Donors Common, Stable Solution How Get Common?

Fehr & Gachter (2002) Nature 415:137. Human Evolution: Dangerous Hunts, Conserve Resources, Warfare Why Do Humans Invest in Costly Activity? Kin Selection, Reciprocity Costly 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 Riders Altruistic 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 Investors Hypothesis: Free Rider Later Cooperates Group Composition Changed Frequently

Fehr & Gachter (2002) Nature 415: Larger Degree of Defection Incurs Larger Punishments 2.Strength of Punishment Stable Across Time 3.Frequencies?

Fehr & Gachter (2002) Nature 415: 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: Subjects Choices (Bars) First 2 Periods, SFI Preferred After Period 5, SI Strongly Preferred 2. Average Contribution to Public Good (Symbols) SFI Declines to 0 SI 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