Nice interesting read.

Among other things, friends are people you count on to come to your aid when you need help. If you were at a bar and a stranger started acting aggressively towards you, for example, you would expect your friends to rush over to help you rather than just stand there, mojito in hand. Contrary to our feelings of human exceptionalism, however, ours is not the only species of primate to create and maintain friendships.
For years primatologists have been puzzling over “friendship” in baboons. Across baboon species lactating females keep up close social relationships with unrelated adult males. The females are not reproductively available, and by devoting much of their attention to these females the males significantly reduce their opportunities to mate with other females, so why are these males so concerned with mothers and infants? What is the function of this behavior?
Several hypotheses have been forwarded. Perhaps friendship is a defense against infanticide, a way to reduce harassment of mothers and their infants by other group members, or a way for mothers to get their infants to bond with particular males so that they will continue to reap social benefits (such as food sharing and support during fights) as they mature. Of these, however, friendship as an anti-infanticide mechanism appears to be best-supported, especially since infanticide is a major cause of mortality among infant Chacma baboons. Baboon social groups are centered around female families that stick together, but males often move from one group to another. As a result immigrant males occasionally supplant the group’s dominant male, and when this happens among Chacma baboons the new alpha picks off the group’s infants one-by-one (hence the group’s females come back into estrus sooner). In such situations a friendship between a male and female baboon can make the difference between life and death for her offspring.
via “You just call out my name…”: Friendships in Male and Female Baboons : Laelaps.