Patterns and trends in primate pair bonds

Pair-bonding may be a significant feature of the social repertoire of some primate species. However, discerning inter- and intraspecific pair bonds is problematic. I present an overview of the general behavior and ecology of species reported to occur in two-adult, pair-bonded groups. There is no two-adult grouped nonhuman primate species in Africa and only two types in Asia. Behavioral and ecological data suggest that the two-adult group or pair-bonding or both may have evolved separately 4-7 times. I propose that two pair-bond components-social pair bond and sexual pair bond-occur and can be defined and described in such a manner that facilitates comparative analysis across primate taxa. The evolution of grouping patterns in many two-adult grouped primates may be best modeled via evolutionary scenarios relying on direct dietary/energetic constraints, predation, and possibly mate-guarding. There is little support for the infanticide prevention and bodyguard hypotheses of female-choice models.