THE EVOLUTION OF COOPERATIVE STRATEGIES FOR ASYMMETRIC SOCIAL INTERACTIONS

摘要

How can cooperation be achieved between self-interested individuals in commonly-occurring asymmetric interactions where agents have different positions? Should agents use the same strategies that are appropriate for symmetric social situations? We explore these questions through the asymmetric interaction captured in the indefinitely repeated investment game (IG). In every period of this game, the first player decides how much of an endowment he wants to invest, then this amount is tripled and passed to the second player, who finally decides how much of the tripled investment she wants to return to the first player. The results of three evolutionary studies demonstrate that the best-performing strategies for this asymmetric game differ from those for a similar but symmetric game, the indefinitely repeated Prisoner's dilemma game. The strategies that enable cooperation for the asymmetric IG react more sensitively to exploitation, meaning that cooperation can more easily break down. Furthermore, once cooperation has stopped, it is much more difficult to reestablish than in symmetric situations. Based on these results, the presence of asymmetry in an interaction appears to be an important factor affecting adaptive behavior in these common social situations.