Evolution of friendships among males
Despite the above observations of direct competition among males, the sometimes lethal aggression, the high stress levels during the mating season, the clear dominance hierarchy, and the rank effects on consorting and paternity, male Assamese macaques also exchange a lot of friendly behavior. Males can be observed sitting in body contact with other males as likely as with females or other group members (Schülke et al. 2010) and they groom another male once every 10 hours. Males are not indifferently nice to any other male, though, but concentrate their friendly behavior to on average only three other males with whom they form a close bond. The closer the bond, i.e. the more often the partners can be found in close spatial proximity and the more often they groom each other the more likely they are to form agonistic coalitions against other males. These coalitions serve to attain or maintain high rank in the future which pays off by increased paternity success. A direct link can be drawn from the cumulative strength of a male’s top three social bonds to his future paternity success (Schülke et al 2010). So the friendly behavior that can be observed among males serves a political function in the sense that males try to manipulate others relationships in order to maximize their own benefits.
These findings on friendships among male macaques are perhaps the most important results from monkey research at PKWS to date. Friendships were known from female baboons and male chimpanzees but not from the sex that usually leaves the natal group and therefore is unlikely to live with many genetic relatives. For female baboons the mechanism linking social bonds and reproductive success is not known yet and for chimpanzees the ultimate benefit has never been assessed with genetic paternity analyses. Therefore male Assamese macaques are extremely important for understanding the evolution of friendships in general which is reflected in the positive reactions of the scientific community (e.g. Current Biology 2010) and the press (e.g. NYTimes). The next step needs to be an analysis of partner choice among males to answer the question how males choose their friends. But these are rare events that need long-term observations preferably of several groups.