In most species of the animal world, fathers contribute relatively little to the well-being and provisioning of their young, often no more than their genes (for exceptions, see, e.g., Ridley 1978; Trivers 1985; Clutton-Brock 1991). This is especially true for mammals, where internal fertilization, long gestation and lactation predispose mothers to care for their offspring alone. Since only females lactate, males can contribute relatively little to rearing of young. Due to internal fertilization paternity is never certain. Moreover, during the long periods of gestation males have ample time to desert the impregnated female in order to increase their reproductive success by seeking additional fertilizations with other females. Not surprisingly then, paternal care is found in only a small minority (less than 5%) of all mammalian species (Kleiman 1977; Clutton-Brock 1991; Woodroffe & Vincent 1994). Compared to most other mammalian taxa, however, primates are characterized by a surprisingly high level of male–infant affiliation or “male care”: Nearly 40% of all primate genera have been reported as exhibiting “direct male parental care” (carrying, retrieving, protecting, provisioning, grooming and/or huddling with young) – the highest percentage for any individual mammalian order (Kleiman & Malcolm 1981).
While there are reasons to remain skeptical about whether all of these observations are correctly classified as “male care” (e.g., Hrdy 1976; Packer 1980), or whether male care is really widespread among all of the species mentioned (Maestripieri 1998), this high level of male–infant affiliation is unexpected and, more importantly, does not seem to be well understood.