For example, mating behavior may not translate into reproductive success when females mate promiscuously during estrus windows, while care behaviors could serve as a much broader signal to all available females rather than solely to a specific female (e.g. While informative, these tests rely on assumptions that are potentially problematic.

Studies have depended on indirect proxies such as mating behavior, males’ choice of infant social partner(s), or the timing of males’ care behaviors relative to mating opportunities 2, 3, 5, 9, 17, 18, 19.

While the mating effort hypothesis has been a source of much speculation, empirical evidence for it has been sparse. the mating effort hypothesis 2, 15, 16, 17). Alternatively, males may be investing in their future reproductive success, rather than their current offspring, if affiliating with infants improves their chances of siring infants’ mothers’ future offspring (i.e. Evidence for the paternal care hypothesis is now well-established in some of the Old World primate species in which relationships between males and infants are common 7, 9, 10, 11, 12, 13, 14). First, they may selectively interact with their current offspring, thereby engaging in paternal care. Males themselves may benefit from these relationships in two ways. Such relationships appear to have fitness-relevant benefits for infants, such as improved access to resources, and protection from infanticide, predation, and conspecific harassment 6, 9, 10, 11. However, they are observed in some Old World primates, including baboons, macaques, gorillas, and humans 2, 3, 4, 5, 6, 7, 8. Social relationships between adult males and infants are quite rare among group living mammals, due to the relatively high payoffs for males of investing in mating rather than parenting 1. These findings establish a link between males’ fitness and their associations with infants in the absence of kin discrimination or high paternity certainty, and suggest a strategy by which selection could generate more involved male parenting among non-monogamous species. Predictive margins indicate males in the top affiliation tertile can expect to sire approximately five times more infants than males in the bottom tertile, across the course of their reproductive careers.

Here we demonstrate that, independent of multiple controls for rank, age, and siring opportunities, male gorillas who affiliated more with all infants, not only their own, sired more offspring than males who affiliated less with young. Males frequently affiliate with infants despite not discriminating their own from other males’ offspring, raising questions about the function of this behavior. Mountain gorillas, which often organize into multi-male groups, are an intriguing exception. Although these predictions are generally met, in some promiscuous primate species males overcome this by identifying their offspring, and providing benefits such as protection and resource access. Socioecological theory predicts that male parenting among mammals should be rare due to the large payoffs of prioritizing mating effort over parenting.

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