Sex at Dawn

William J. Hamilton and Patricia C. Arrowood analyzed the copulatory vocalizations of various primates, including three human couples going at it.⁹ They noticed that “female sounds gradually intensified as orgasm approached and at orgasm assumed a rapid, regular (equal note lengths and inter-note

intervals) rhythm absent in the males’ calls at orgasm.” Still,

the authors can’t help sounding a tad let down when they note, “Neither sex [of human] ... showed the complexity of note structure characteristic of baboon copulatory vocalizations.” But that’s probably a good thing, because elsewhere in their article we learn that female baboons’

copulation calls are clearly audible to even human ears from

three hundred meters away.

Before you conclude that female copulatory vocalization is just a fancy phrase for a little excitement, think about the predators possibly alerted by this primate passion. Chimps and bonobos may be out of reach up in the branches, but baboons (like our ground-dwelling ancestors) live among leopards and other predators who would be quite interested in a two-for-one special on fresh primate—especially given a mating pair’s distracted, vulnerable state.

As Hamilton and Arrowood put it: “In spite of the risk of exposure of individuals and the troop to predators these baboons habitually call during copulation, [so] the calls must have some adaptive value.” What could that be? The authors offered several hypotheses, including the notion that the calls may be a stratagem to help activate the male’s ejaculatory reflex, an analysis with which many prostitutes would presumably agree. Perhaps there is something to this idea,¹⁰ but even so, male primates are not known for needing a great deal of assistance in activating their ejaculatory reflex. If anything, the human male ejaculatory reflex tends to be too easily activated—at least from the perspective of women not being paid to activate it as quickly as possible. Especially given all the other convergent evidence, it seems far more likely that in humans, female copulatory vocalization would serve to attract males to the ovulating, sexually receptive female, thus promoting sperm competition, with all its attendant benefits—both reproductive and social.

Yet despite all the loud carrying on by women the world over, “The credo of the coy female persists,” writes Natalie Angier. “It is garlanded with qualifications and is admitted to be an imperfect portrayal of female mating strategies but then, that