The Strategic Dynamics of Cooperation in Primate Groups

The processes that influence the distribution of benefits to other group members have been central themes in evolutionary biology over the last 30 years. There is a broad consensus that kin selection underlies altruistic behavior among genetic relatives and that nepotistic altruism is common in nature. In contrast, there is much less agreement about the processes that underlie beneficent behavior toward nonrelatives or the importance of such processes in nature. Early enthusiasm for reciprocal altruism has given way to caution, as few robust examples of contingent reciprocity, turn-taking, and exchange have been found in nonhuman animal species. This has generated interest in a broader range of processes, such as coordination and collaboration, that may favor helpful behavior toward nonkin. Here, I review observational and experimental evidence about turn-taking, collaboration, and coordination in primate groups. I describe four game-theoretic models in which individuals can benefit from providing help to others (Iterated Prisoner's Dilemma, Stag Hunt, Battle of the Sexes, and Games of Chicken) and argue that the formal payoff structures derived from these models provide a clear and cogent framework for understanding the processes underlying various types of cooperative interactions. I use this framework to review observational and experimental evidence of cooperation among primates. Research conducted by behavioral ecologists has focused mainly on turn-taking, and studied situations that correspond loosely to the Iterated Prisoner's Dilemma model. Naturalistic research documents the pattern of associations between help given and received and explores the temporal span of reciprocity and the currencies exchanged. Experimental work on the Iterated Prisoner's Dilemma has been designed to illuminate the contingencies between giving and receiving benefits. Evidence for contingent reciprocity in nature and the laboratory is inconclusive for primates, leading some to suggest that cognitive constraints on memory and psychological biases that favor immediate rewards over delayed rewards preclude contingent reciprocity. Research conducted by comparative psychologists has mainly focused on the cognitive and psychological capacities that enable animals to cooperate effectively. This work focuses on situations in which animals must work together to achieve a joint reward, a situation that corresponds loosely to the payoff structure of the Stag Hunt model. Primates succeed in some collaborative tasks in the laboratory, but not in others. Success seems to be facilitated by tolerance of partners, expectation of obtaining rewards, and having some understanding of the requirements of the task. Coordination problems, which correspond loosely to the payoff matrix of the Battle of the Sexes game, have been given considerably less attention, although animals must solve many coordination problems in the course of their everyday lives. A limited body of evidence suggests that some primates have evolved vocalizations which serve as honest signals of intent, and facilitate coordination of group movements and social interactions.