Altruism. Why Are Organisms Ever Altruistic? Kin Selection. Reciprocal Altruism. Costly Signaling. Group Selection?

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1 Altruism Nepotism Common-Pool Resource (CPR) Tragedy of the Commons Public Good Free-riders Competitive Altruism A 1987 Florida news story reported that 22 blood donors who had false positives on an HIV test were misinformed that they were HIV positive, & 7 committed suicide. This story prompted Gerd Gigerenzer and colleagues to study how HIV counsellors were explaining the results of HIV tests. One of the researchers approached 20 HIV counselors for a blood test, presenting himself (truthfully) as a 25-year old heterosexual with no history of drug use. In each clinic he asked a standard set of questions including What is the probability that a male in my risk category actually has HIV after a positive test? What s the right answer? (Experts ought to know!) Relevant facts that the expert counselors should have known : HIV prevalence rate among low-risk men in Germany in 1990: 0.01 % Test sensitivity (probability of correct detection given disease): 99.9 % (so the miss rate = 0.1 %) Test specificity (prob of correct healthy diagnosis if no disease): % (so the false positive rate = 0.01 %) Relevant facts that the expert counselors should have known : HIV prevalence rate among low-risk men in Germany in 1990: 0.01 % Test sensitivity (probability of correct detection given disease): 99.9 % Test specificity (prob of correct healthy diagnosis if no disease): % The counselors answers: 2 refused to answer directly 10 said 100 % certain 5 said 99.9 % certain 1 said 99 % certain 2 said 90 % certain Working it out by Bayesian inference: p ( HIV+ + test) = p ( HIV+ ) x p ( + test given HIV+ ) p ( HIV+ ) x p ( + test HIV+ ) + p ( HIV- ) x p ( + test HIV- ) The counselors estimated between 90 and 100 %. The correct (Bayesian) answer is 50 %! And there s an easy way to figure it out: Imagine 10,000 men. Expected number HIV+ = 1 (and he ll almost certainly test positive) men are not HIV+, and with a false positive rate of 0.01 %, one of them (on average) will test positive, too. Result? 2 positive tests: 1 truly HIV+, 1 not. 10,000 men 1 HIV HIV- Why Are Organisms Ever Altruistic? Kin Selection Reciprocal Altruism Costly Signaling Group Selection? 1 pos test 0 neg test 1 pos test 9998 neg tests G. Gigerenzer (2002) Calculated risks. Simon & Schuster 1

2 Within-household Homicides in Detroit, 1972 Blood Kin are Relatively Immune, given their Availability Non-Nepotistic Sociality Homicides per Million Potential Victims Spouse Non-Rel Child Parent Other Rel The problem of altruism and its second solution (after nepotism) : Cooperation and Reciprocity (direct and indirect). Common Pool Resources and the Tragedy of the Commons. escaping the tragedy. Public Goods Games : why contribute? Punishing non-cooperators is also hard to explain. Reputation effects Ultimatum Games Daly & Wilson (1982) American Anthropologist 84: Axelrod s tournament showed that reciprocal altruism can evolve if individuals interact more than once. Question: What if individuals meet each other individual only once? Is cooperation doomed? "Indirect Reciprocity - Altruistic acts that are unlikely to be directly reciprocated may still benefit the altruist later if his reputation is enhanced, and others reward those with altruistic reputations. If an individual refuses to be altruistic, then it decreases his reputation, and lowers his chances of having others behaving altruistically towards him. Thus, an individual can benefit from being altruistic if others notice. Nowak & Sigmund (1998) showed with a computer simulation that indirect reciprocity can evolve if individuals help only those who have a good reputation. Using an evolutionary simulation, they found that gradually, the amounts of altruism increased, and the number of defectors decreased because only the strategies that were selectively altruistic thrived. Do People Actually Do This? Wedekind and Milinski designed an experiment that gave the opportunity for indirect reciprocity to occur. They formed groups of 9-10, and gave each player 7 francs. Players were randomly assigned to be Donors or Recipients (6 times each) with a different person each time. Donors could pay 1 or 2 francs to give 4 francs to Recipients. Identities were concealed, and players were identified only by number, but their past decisions of giving or non-giving were displayed. Nowak & Sigmund (1998), Nature, v.393, pp This is the mechanism used by Wedekind & Milinski to ensure anonymity, yet provide information about player s past decisions Participants had an image score. Every time they chose to give money, their image score increased by one. Every time they refused, their image score decreased by one. Did a participant s image score affect how others behaved towards him/her? Wedekind & Milinski (2000) Science, 288(5467), Image Did Affect Amount Received The image score of recipients who were given money tended to be higher than the image score of recipients who were not given money (in 7 out of 8 groups), p < Donors were more likely to be altruistic towards those who had been altruistic in the past, even though the donors would not benefit from the recipients directly. Donors benefited from having an increased image score, which increased the amount money they received from others (indirect reciprocity). 2

3 Donors who only donated once or twice only gave those donations to players with high image scores; donors who gave more often were less discriminate. Wedekind & Milinski (2000) Science, 280(5467), Altruism Towards Groups In group situations, people cannot always direct their actions towards specific individuals, e.g. public goods and common pool resources Common Pool Resources (CPRs) CPRs are resources that people have collective rights and/or abilities to use, and whose value is depleted by each individual s use. CPRs "invite" free-riders : Some CPRs (e.g. pastures and fisheries) exist regardless of human labour. Others (e.g. irrigation systems) are built. In either case, there is a strong incentive to exploit CPRs without contributing to their maintenance or development: If some take benefits without paying their share, those who do pay are "suckers". This is the tragedy of the commons. In the classic e.g., each shepherd keeps adding sheep to his flock despite evidence that the commons can t sustain so many. Modern e.g.s of similar social traps include collapse of fisheries in the north Atlantic and elsewhere. Preventing Free-riding Public Goods Like the necessity for cheater detection in dyadic reciprocity, Elinor Ostrom and others have identified the monitoring and sanctioning of free-riders as essential for preventing tragedy and maintaining CPRs. Ostrom s claim that an institutionalized capability for monitoring and sanctioning free-riders is essential for successful long-term maintenance of Common Pool Resources in real world situations rests on analysis of case histories: both success stories and tragedies of over-exploitation. Public goods (CPR) experiments can test this claim. Something that individuals have to expend effort to provide (an altruistic effort), and once it is provided, everybody benefits from it. No one in the group can be excluded from benefiting. Examples: national defense, public radio, public radio, big-game hunting, group projects in university Selfish Interest vs. Group Altruism How do we study this sort of problem? The group will do best if everyone cooperates, but it is in each individual s interest to defect and free-ride on the work of others. How is any group cooperation sustained? How can public goods be provided? Some experimenters use Public Goods Games. In these games, each individual is given an amount of money that they can either keep or donated to their group. Any money that is donated increases in value, and is then shared equally amongst all the participants. Group profits are highest if everyone donates all their money. However, each player does best if they do not donate anything. i.e. They take the benefit from the group (share of the profits) without paying the cost (donating) 3

4 A Typical Public Goods Game Each member of the group (e.g. 4 people) receives some money (e.g. $10) each round which they may either keep for themselves or donate to the public good. The total amount donated is multiplied by a factor greater than 1 (e.g. it s doubled), and this amount is shared equally by all the players regardless of their individual donations. Examples If A donates $10 to the group (and keeps nothing) and everyone else also donates $10, the total amount donated is $40. This amount is doubled = $80. Each player gets a $20 share from that, so they each make $20 that round. However, if A had kept his $10, but everyone else donated $10, the group would earn $60, and he would get a $15 share of that, for a total of $25, and the others get $15 each. Thus, each individual has a temptation to sucker the others, or avoid being suckered. Typical Results Most players donate some (not all) of their money to the public good, and donations fall over successive rounds because no one likes being the sucker. This fall is faster when players know individual contributions rather than group averages. Most public goods games are played anonymously, so that no player knows the identity of any other player. Chapter 15 describes how donations in Dictator games are more selfish under double-blind conditions than when the experimenter knows each person s decisions. Might the donations in public goods be higher if other players knew who donated and who defected? What happens without anonymity? % of e n d o w m e n t Period Anonymous Non- Anonymous + Interaction Donations were higher when participants knew how much each other person donated and the participants had a chance to interact before the game (p <.001) Data from Gächter & Fehr (1999), J. Econ. Beh. & Org, 39, Rege & Telle (2001) also found that donations increase when donations are not anonymous, and the game is explicitly framed in terms of cooperating and free riding. However, there is a fairly constant proportion of people who freeride regardless of anonymity or framing. Number of subjects Does everybody donate more? Anonymous Anon./group frame Non-anon. Non-anon/group frame 0% 1%-99% 100% Why should we care if people know? Recall: In reciprocal altruism and the repeated Prisoner s Dilemma, you can punish other players by returning defection with defection. Punishment is selective. However: In a standard public goods game (N>2), you can only punish by reducing your own contribution. This punishes everyone else whether they are cooperators or defectors! 4

5 Why should we care if people know? Fehr & Gächter (2000) introduced a mechanism to selectively punish free-riders in public goods games. After each round, each player was given the option of paying a cost to reduce the payoff of any other player. This is a financial punishment, but there was a cost of inflicting it. Fehr & Gächter (2000), American Economic Review, 90, When players could punish specific players, contributions stayed high, and even increased. Without punishment, those same players showed a decline in contributions, just like in any other public goods game. Notice the sharp contrasts between the end of rounds without punishment and rounds with punishment People were even willing to punish other players when the groups were randomly shuffled every round, and this kept contributions stable when punishment was allowed. Fehr & Gächter (2000) Free-riders got punished more than cooperators, and the amount of punishment was related to how badly the person free-rode. Partner = group composition remained the same all rounds Stranger = group composition shuffled each round They later ran a session where participants were randomly shuffled, and guaranteed to never encounter the same 4- person group. Punishments and contributions were similar to when there was still a chance of meeting again. Fehr & Gächter (1999) Working Paper No. 10 As a result of the opportunity to punish, group payoff increased when punishment was possible, even after subtracting the cost to punish. Is punishment the best way to play? Non-punishers do better than punishers, because they freeride on the costly punishment of the punishers. Thus, there is a second-order free-rider problem because punishment is a public good. We can try to solve this by punishing non-punishers. Gintis (2000) proposes the model of strong reciprocity to explain this. Strong reciprocators are individuals who are predisposed to cooperate, or punish non-cooperators. Such individuals succeed because they cause the success and survival of whatever groups that they happen to be in. Alternately, can rewards explain altruism? Might individuals benefit from having a reputation for being altruistic? Can reputation explain giving? Milinski et al. combined public goods games and their indirect reciprocity game. Participants were in one of two conditions: 1) 8 rounds of public goods, then 8 rounds of indirect reciprocity 2) Alternating rounds of indirect reciprocity and public goods (8 each) Participants then played 4 final rounds of public goods, where they were either told that they would have no more rounds of indirect reciprocity, or not given that information (and would thus expect future rounds of indirect reciprocity). This led them to 2 research questions; 1) Are donations to the public good higher when participants stand to benefit from rounds of indirect reciprocity? 2) Are participants who contribute to the public good more likely to receive money via indirect reciprocity? Milinski, Semmann, & Krambeck (2002), Nature, 415,

6 Donations to public goods were significantly higher when they were alternated with rounds of indirect reciprocity (p < ), plus no decline in contributions; players had the chance to be rewarded for contributing to public goods. Contributions declined once participants knew that no more rounds of indirect reciprocity remained. Red = public goods 1st, then indirect reciprocity Blue = alternating rounds filled circles: rounds of public goods open circles: rounds of indirect reciprocity squares: group knew that indirect reciprocity rounds were finished diamonds: group didn t know that no more indirect reciprocity left Participants who donated to public goods were less likely to be refused money in the rounds of indirect reciprocity (i.e. they were more likely to receive money) Groups that alternated rounds of public goods and indirect reciprocity earned more money than those that played the games in blocks of 8 each. Milinski, Semmann, & Krambeck (2002), Nature, 415, Altruism as a Costly Signal? - Can signal willingness to cooperate - Can signal abilities e.g. philanthropy, hunting Could Competitive Altruism exist? Take-Home Message: There can be benefits from having a good reputation and being altruistic: - you receive the benefits or mutual cooperation - you receive more altruism from others - you don t get punished for being selfish Under certain conditions, altruism can be selected for! 6