Evolution of alliance in primates: A population genetic model

Alliance behaviors in anubis baboons, chimpanzees, Japanese monkeys, and rhesus monkeys are briefly described. Alliance differs from simple altruism or cooperation between 2 individuals in that a third conspecific individual, the common enemy, is adversely affected. Two models of alliance formation are considered, one in which support is given unilaterally and the other in which both parties can profit. It is assumed that the allies are equally related to each other and to the common enemy. Using a quantitative genetic model, conditions are derived for alliance behavior to be selectively advantageous. The models are applied to reciprocal altruism between adult male anubis baboons and manipulation by adult male chimpanzees. It is argued that reciprocally altruistic alliance in baboons as described is difficult to reconcile with theory.