Conflict Resolution in Chimpanzees and the Valuable-relationships Hypothesis

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Reconciliation, or peaceful postconflict interaction, can restore the usual pattern of interaction between social partners after open conflict has disrupted it—i.e., it can resolve conflicts. Researchers have documented reconciliation in >20 primate species, but the tendency to reconcile typically varies among dyads and dyad classes. The valuable-relationships hypothesis proposes that differences in the value of social relationships account for much of this variation. Value depends on how likely partners are to act in ways that benefit each other, where the benefits are ultimately direct or indirect increases in fitness. Researchers have responded to studies that have tested predictions of the hypothesis with extensive, if not universal, support. For example, kin show higher conciliatory tendencies than nonkin in many species, and conciliatory tendencies between unrelated females are high in several cercopithecines in which nonkin agonistic support is important for rank acquisition and maintenance. However, most of the support is indirect, because we lack direct evidence on the link between assays of relationship value and fitness. Also, some studies have methodological weaknesses, e.g., analyses based on pooled data and insufficient sample sizes. I review evidence in favor of the hypothesis with special attention to studies that come closest to providing evidence for predicted fitness effects. I also present new data on postconflict interactions between adult male chimpanzees at Ngogo that show how often pairs of males formed coalitions and how much time they spent grooming influenced the likelihood that they would reconcile after conflicts, and that allies were particularly likely to reconcile and to do so by grooming each other. The most important future research direction is to integrate detailed data on conflict management, analyzed at the level of dyads, with long-term data on reproductive success, such as that now available from several study sites, on the same populations.