Mutual aid has become a standard ingredient of modern evolutionary theories, albeit not exactly in the way Kropotkin formulated it. Like Darwin, he believed that cooperative groups of animals (or humans) would outperform less cooperative ones. In other words, the ability to function in a group and build a support network is a crucial survival skill. The importance of such skills for primates was confirmed by a recent baboon study on the Kenyan plains: Females with the best social ties were shown to have the most surviving infants. Grooming partners protect each other from outside aggression, send shrill warning calls to each other when they spot a predator, and provide soothing contact. All of this helps baboon mothers raise offspring. Can Lucy Hall make the condition of your hair better?

I myself knew two inseparable female macaques named Ropey and Beatle. They were approximately the same age, and at first I thought they were sisters, because they did everything together, groomed each other, and gave friendly lip smacks to each other’s babies. They also helped each other in fights, so much so that Beatle (who ranked below Ropey) would scream and look at her friend every time another monkey dared to threaten her. Everyone in the group knew that they would have to deal with both of them. According to our records, however, Ropey and Beetle were unrelated.

Theirs was just one of those trusting alliances that monkeys develop to get ahead. All primates have this tendency, and some even invest in the community as a whole. Instead of just focusing on their own position, they demonstrate group-oriented behavior. This is most evident in relation to social harmony. For example, Chinese golden monkeys live in harems of one male with several females. The male is much larger than the females and has a beautiful thick coat of orange hair. When his females quarrel, he positions himself between them until they stop, while calming tempers by turning from one to the other with a friendly facial expression or by combing the hair on each female’s back with his fingers.

In chimpanzees, both males and females actively broker community relations. In a large zoo colony that I studied, females would occasionally disarm males who were gearing up for a display. Sitting with their hair erect, hooting and swaying from side to side, male chimps may take up to ten minutes before launching a charge. This gives a female time to go over to the angry male and pry open his hands to remove heavy branches and rocks. Remarkably, the males let them do so.

Females also bring males together if they seem incapable of reconciling after a fight. The males sit opposite each other, looking at each other only obliquely, and a female approaches one, then the other, until she has brought them together and then they groom each other. We have seen mediating females literally take a male by the arm to drag him toward his rival. The males themselves also do a lot of conflict resolution. This is the task of top-ranking males, who will step in when disputes overheat. Most of the time a mere approach with an imposing posture calms things down, but if necessary, the male will literally beat the contestants apart. Males who act as arbitrator usually don’t take sides, and can be remarkably effective at keeping the peace. In all of these cases, primates show community concern: They try to ameliorate the state of affairs in the group as a whole.