The Patterning of Intervention among Male Bonnet Macaques: Reciprocity, Revenge, and Loyalty

For those interested in the evolution of human societies, the scale of human social organization presents an interesting problem. A number of authors have argued that human social organization involves cooperation that is too widespread to be explained by nepotism or kin selection (Alexander I987; Boyd and Richerson I990; Campbell I975, i983). Instead, they have suggested that widespread cooperation in human societies may be based upon reciprocity. This argument relies upon the theory of reciprocal altruism (Trivers I97 I), which predicts that reciprocity will be favored by natural selection if individuals restrict their help to those who help them in retum. This process is favored because, over time, the participants in reciprocal relationships obtain benefits that balance the costs of their interactions. In contrast to kin selection, reciprocity does not rely upon the participants' being kin. This insight has generated considerable theoretical and empirical interest in the factors that may shape the evolution of cooperative behavior. There have been a number of efforts to formalize and expand Trivers's original theoretical formulation (reviewed by Axelrod and Dion I989, Boyd n.d.), and there has also been considerable interest in empirical evidence of cooperative behavior in other mammalian species, particularly the nonhuman primates. Since the nonhuman primates are our closest living relatives, analysis of the patteming of cooperative activities among them may provide important insights into the phylogenetic history of the cognitive and behavioral mechanisms that underlie reciprocity in humans. Coalitions provide a particularly useful context in which to study the patteming of cooperation in nonhuman primates. A dyadic confrontation is transformed into a coalition when a third individual intervenes on behalf of one of the original participants. Although it is impossible to assess quantitatively the effects of specific behavioral acts upon lifetime fitness, coalitions are generally considered to be a form of altruism which is beneficial to the recipient and costly to the donor (see Dunbar I988 for a full discussion of this issue). The individual who receives support may benefit if intervention increases the probability that the opponent will flee, submit, or redirect its aggression to the supporter. The supporter may suffer some costs if it expends energy, suffers an injury, or becomes the target of the opponent's aggression. Over the last I5 years, the frequency and patteming of support in agonistic interactions have been described in a variety of primate species. While differences in sampling techniques, behavioral definitions, and methods of analysis make it difficult to compare these studies directly, some general conclusions emerge from them: individuals tend to give the most support to their relatives, and the tendency to support kin is particularly pronounced in confrontations with older, larger, or higher-ranking group members (e.g., Gorilla gorilla gorilla [Harcourt and Stewart, I987, I989], Pan troglodytes [de Waal i9821, Papio ursinus [Cheney I9771, Cercopithecus aethiops [Cheney I983, Horrocks and Hunte I983], M. mulatta [Bemstein and Ehardt I985, Kaplan I9771, M. fascicularis [de Waal I978], M. nemestrina [Massey I9771, M. radiata [Silk i982], M. fuscata [Kurland I977, Watanabe I9791). However, not all support is performed on behalf of kin; virtually all of the studies cited above report that monkeys and apes sometimes support unrelated individuals. Reciprocity in support was first reported among unrelated male baboons, which form coalitions in contests over access to estrous females (Packer I977). Similar coalitions have subsequently been described at several other sites, although the extent of reciprocity in support among males has been questioned (Bercovitch I988, Nod i989). Reciprocity in support has also been documented among vervet monkeys (Hunte and Horrocks i987) and macaques (de Waal and Luttrell i988). Seyfarth and Cheney have demonstrated that vervet monkeys and baboons provide support in agonistic interactions for individuals that groom them (Cheney I977; Cheney and Seyfarth I990; Seyfarth I977, I980), although this does not seem to hold true for female bonnet macaques (Silk i982) or rhesus macaques (de Waal and Luttrell i986). Seyfarth and Cheney (i984) performed a particularly insightful experiment in which they explored the conditions under which grooming might be exchanged for support among free-ranging vervet monkeys. In this experiment, a tape-recorded distress call was played back to a subject from a hidden speaker under two different conditions: (a) after it had been groomed by the caller and (b) when no grooming had been observed. Uf the subject had been groomed by the caller it was more likely to respond to the distress call by staring intently in the direction of the speaker. When the subject and caller were closely related, the subject's response was not influenced by whether or not the caller had recently groomed it. Seyfarth and Cheney's results demonstrated that one form of altruism, support, was contingent upon another, grooming. They also suggested that the rules for social exchange may vary among kin and nonkin, i. I992 by The Wenner-Gren Foundation for Anthropological Research. All rights reserved ooiI-3204/92/3303-0004$I.00. This work was partially supported by NIH Grant RRooI6g to the California Primate Research Center and a grant to the author from the UCLA Academic Senate. I thank Rob Boyd, Dorothy Cheney, Frans de Waal, Lynn Fairbanks, and several anonymous referees for their comments upon the manuscript.