Natural selection has favored the evolution of physical traits and behavioral strategies that enable individuals to increase the benefits that they gain and reduce the costs that they incur from living in groups. For example, in species that do not form pair bonds, there is competition among males over access to females, and this has favored the evolution of traits, such as body size and canine size, that increase male fighting ability or large testes that increase male sperm volume.
To reduce the risk of inbreeding, members of one or both sexes routinely leave their birth groups (disperse) when they reach the age of sexual maturity and move to new groups. Primates also demonstrate some forms of “behavioral immunity” that enable individuals to reduce their exposure to pathogens. For example, some primates avoid grooming animals that are infected with certain parasites.
In some species, individuals form close relationships that help them to cope with social challenges. These relationships play an important role in cooperative activities, such as grooming and alliance formation, and may play an important role in regulating stress.
Written by Joan Silk PhD