Cooperate with Equals: A Simple Heuristic for Social Exchange

The chapter shows that a simple heuristic, which directs cooperation toward economic equals and defects on other individuals, facilitates cooperation in social environments where individuals engage in multiple, nonrepeated prisoner's dilemma games with partners whom they know little about. The heuristic produces successful cooperation due to its ability to infer whether or not its partner in a social encounter employs the same heuristic-not whether that partner is cooperative per se. As noted in previous research and elaborated upon here, this property prevents the heuristic from suffering exploitation and it also impedes easily exploited cooperative strategies from proliferating in conditions of ubiquitous cooperation. These aspects of the strategy, furthermore, yield insight into the environments in which the heuristic fosters high levels of cooperation. The heuristic best succeeds at producing cooperation in social environments where agents involve themselves in a moderate number of low information, one-shot prisoner's dilemma games per generation. As the number of such encounters increases per generation, the strategy more frequently defects on its social partners. Nonetheless, the heuristic cultivates cooperation in social environments where interactions are not repeated, opportunities for punishment do not exist, and agents have no direct information about their partner's past cooperativeness.