All primates are social animals: they interact regularly with other members of their species in various ways. The composition of primate social groups differs considerably from species to species. Many primate species live in groups consisting of a single adult male along with several females and their offsprings. In contrast to these one-male groups, many species live in large polygynandrous groups that include several reproductively active adult males, females, and offsprings, all of which forage as a group. These categories of social organization provide us mainly with a convenient framework for comparing different species. The ultimate goat of such classification is to facilitate the investigation of the factors that have given rise to this diversity in social organization.
Primate social groupings are the result of many selective factors, each of winch influences in a different way on the size, composition, and dynamics of the social group. Although most primates are found live in species-specific types of social units, most individuals do not spend their entire lives in the same social group. In most Old World monkeys and in several lemurs, females generally stay in their natural group, and males emigrate to other groups. In chimpanzees and bonobos, most males stay in their natural group, and females migrate. In many other species, both sexes migrate from group to group. From the perspective of the individuals, primate social group are not stable, permanent units: they are complex and dynamic networks that continually change as individuals are born, mature, emigrate, immigrate, mate, reproduce and die. Factors such as inbreeding avoidance, resource distribution, and protection from infanticide seem to be important in determining the patterns of immigration and emigration in different species.
