This paper provides strong evidence challenging the self-interest assumption that dominates the behavioral sciences and much evolutionary thinking. The evidence indicates that many people have a tendency to voluntarily cooperate, if treated fairly, and to punish noncooperators. We call this behavioral propensity “strong reciprocity” and show empirically that it can lead to almost universal cooperation in circumstances in which purely self-interested behavior would cause a complete breakdown of cooperation. In addition, we show that people are willing to punish those who (...) behaved unfairly towards a third person or who defected in a Prisoner’s Dilemma game with a third person. This suggests that strong reciprocity is a powerful device for the enforcement of social norms involving, for example, food sharing or collective action. Strong reciprocity cannot be rationalized as an adaptive trait by the leading evolutionary theories of human cooperation (in other words, kin selection, reciprocal altruism, indirect reciprocity, and costly signaling theory). However, multilevel selection theories of cultural evolution are consistent with strong reciprocity. (shrink)

Unlike the supergame model assumes agents in exchange situations will normally not be perfectly informed on past behaviour of their partners. Also, they will be able to choose their partners to a certain extend. A formal model is presented that attempts to take account of these facts. It is supposed that for any actor the probability of finding a partner for a lucrative exchange depends on his past behaviour. A model of reputation formation is presented as a formal description of (...) this interdependency. Based on this model it is shown that under certain conditions only co-operative conduct will pay in the long run. Thus it is confirmed that - given the mechanism of trust - rational agents may act trustworthy. (shrink)