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)

Reciprocity is a decisive behavioural rule resulting in successful co-operation or deterrence. In this paper, a dynamic model is proposed, where reciprocity is described by changes in altruistic (or malevolent) ties. Multiple steady states may exist in one of which there may be general cooperation (solidarity) and the other being one of universal malice (war of each individual against all other individuals). We apply our theory to a number of examples, illustrating that the agents’ initial preferences determine whether a steady (...) state of solidarity, selfishness or malice will emerge. (shrink)

Trusting in someone's cooperation is often connected with the danger of being exploited. So it is important that signals are exchanged which make it probable enough that the potential partner is reliable. Such signals must be too expensive for partners who are planning to abuse the trust they are given but cheap enough for those who wish to initiate a long-term cooperation. In a game theoretical model, it is shown that such signals could consist of presents given before the partnership (...) starts. (edited). (shrink)