Abstract
Prisoner's dilemma is often considered a model of social phenomena. However most PD studies are limited to isolated dyadic relations, which is not considered to be embedded in a large network structure. To generalize the findings of PD studies, we need to overcome this limitation. The purpose of this paper is to extend PD studies to multiple PD relations among group members. This new paradigm is called the “prisoner's dilemma network.” What makes the PD network distinct from the 2-person PD is the option for choosing partners. In the PD network situation, “PD pairs” come into existence only by mutual selection, such that a relationship between specific two persons may be short-lived. In such a situation, tit-for-tat (TFT) strategy, that has been proven to be effective in isolated PD relations in promoting mutual cooperation, may not be effective. To find out what strategies are effective in PD network situation, a contest of computer programs was held. In the results of this contest, out-for-tat (OFT) strategy showed its effectiveness. OFT is the strategy that assigns the first priority to the partner of the last trial unless the partner defected there. Because OFT has four features of TFT: niceness, simpleness, responsiveness, and forgivingness, it may be said that the OFT strategy is the “TFT on partner selection”.
