Practicing Hamilton's rule: Kin selection in primate groups

The kin selection bandwagon has been rolling for several decades in behavioral ecology, gaining speed and momentum. There is abundant evidence for kin biases in behavior (nepotism) in many animal species, and most behavioral ecologists have taken this as crude, but convincing evidence that kin selection (Hamilton 1964) is operating. However, Dawkins' 'sensitive ethologist' may have begun to detect a new chorus of 'skeptical growls' about the role of kin selection in shaping cooperative behavior in animal groups (Chapais 2001, Clutton-Brock 2002). These critiques focus on three issues. First, in cooperatively breeding vertebrates, behavior that has been commonly attributed to kin selection may actually enhance individual fitness directly (Clutton-Brock 2002). In a broad range of species, some types of behavior that have been categorized as altruistic may actually benefit the actor (Chapais 2001, Chapais & Bélisle 2004, Chapais, this volume). In these cases, mutualism or simple self-interest may operate, not kin selection. Second, competition between relatives may counteract the effects of kin selection, limiting the prospects for the evolution of altruism by this route (West et al. 2002). Third, kin biases in behavior may be the product of processes besides kin selection. If social interactions are enhanced by familiarity, then initial kin biases in association patterns may lead to kin biases in behavior, but the dynamics of interactions may be shaped by mutualism, reciprocity, or individual benefits rather than kin selection (Chapais 2001, Chapais & Bélisle 2004).