Evolution of Pairwise Commitment and Cooperation

When starting a new collaborative endeavor, it pays to establish upfront how strongly your partners commit to the common goal and what compensation can be expected in case the collaboration is violated. Diverse examples in biological and social contexts have demonstrated the pervasiveness of making prior agreements on posterior compensations, suggesting that this behavior could have been shaped by natural selection (Nesse, 2001; Han, 2013). We discuss here our work in (Han et al., 2013), wherein we analyze the evolutionary relevance of such a commitment strategy in the context of the pairwise one-shot Prisoner’s Dilemma (PD). The commitment strategy proposes, prior to any interaction, its co-player to commit to cooperate in the PD, paying a cost to render the commitment deal reliable (e.g. the cost to hire a layer to make a legal contract). Those players that commit and then default (i.e. defects) have to compensate their nondefaulting co-player. Resorting to methods of Evolutionary Game Theory (Sigmund, 2010), we analyze, both mathematically and using numerical simulations, the viability of such a commitment strategy in the copresence of different free-riding strategies, including the one that commits but then defaults on the commitment, and the one that commits and cooperates only if someone else pays the cost of arranging the commitment (namely, this strategy defects if there is no commitment in place). Our results show that when the cost of arranging a commitment deal is justified with respect to the benefit of cooperation, substantial levels of cooperation can be achieved, even without repeated interactions. On the one hand, commitment proposers can get rid of those individuals that agree to cooperate yet act differently, and, on the other hand, they can maintain a sufficient advantage over those that cooperate only if the commitment is set up by someone else, because a commitment proposer will cooperate with players alike herself, while the latter defect among themselves.