Abstract
Masculine traits in human males are expressed in face and shoulder morphology, vocal pitch, and body odour, as well as through behavioural predispositions, including competitive status striving, aggressive reactivity, and high reproductive effort at the expense of paternal investment. As this article demonstrates, this range of traits can be directly linked to the activity of neural crest cells (NCC’s) at embryonic stages of development. Given this linkage, previously observed sexual selection on masculine traits will inevitably affect embryonic NCC activity across a given population. Since selection for suppressed NCC function is the physiological cause of mammalian domestication syndrome, selection for or against masculine male traits must lead to more or less ‘self-domesticated’ lineages among human groups. As such, future research into human sexual selection on masculinity will benefit from an appreciation of NCC function and behaviour, and consideration of the evolutionary implications of human self-domestication. This article provides an original integration of two longstanding fields of significant research interest by demonstrating the proximate physiological—and ultimate evolutionary—causes of sexual selection on human masculinity. In doing so, it also explains a peculiar human behaviour, the shaving of facial hair.
