Examining the evidence for major histocompatibility complex-dependent mate selection in humans and nonhuman primates

Compounds of the major histocompatibility complex (MHC) are integral for effective vertebrate adaptive immune response, and are also implicated as cues for sexual selection. The evidence for this is supportive of MHC-based preference for diverse and dissimilar mating partners, in a range of vertebrates from fish to nonhuman primates. However, the evidence for a similar role of these genes and the evolutionary benefits of their diversity in human mate choice has been more controversial. Here, we review the results of 34 primary studies on MHC-mediated mate choice in humans and nonhuman primates in an effort to understand what processes may underscore, or belie, such differences. Both human and nonhuman primate studies show evidence of mate selection for MHC-dissimilarity and diversity, with fewer results in support of mate selection for optimal diversity or for specific "good gene". In general, stronger support comes from female-choice studies as opposed to male-choice studies (though male preferences and choice are investigated less often). This review suggests that the majority of mate choice results from contemporary human studies are consistent with our evolutionary history, but also reveals that only in humans do we find evidence for preference for mates with similar MHC composition. Overall, we show that contextual nuances, namely, population structure, multiple sensory cues that signal different information, and hormonal influences may explain the conflicting results observed for the role of MHC in human sexual preference, and argue for the exploration of such caveats in less well-studied systems to discern between general patterns and qualities unique to humans.