July 19, 2013
IT IS a question not just of prurient but also evolutionary interest: what was the mating behaviour of our extinct relatives?
With living apes so variable in their sexual preferences, it’s tough to work out the sex habits of the ancestor common to humans and chimps. Gorilla groups contain just one sexually active male and several females, for example, while among chimps, several sexually active males breed with the group’s active females – and vice versa. Humans, meanwhile, show a variety of mating behaviours but often form monogamous couples.
Michael Jensen-Seaman and Scott Hergenrother at Duquesne University in Pennsylvania think that it is the chimps – not humans – that have experimented with new sexual behaviours since our lineages diverged. Uniquely among apes, male chimps produce thick semen that coagulates into a plug in the female’s genital tract. In a society where females mate freely with several males the strategy increases the chances that a male will fertilise the female’s eggs. But did male chimps inherit their mating plugs from the last common ancestor they shared with us or did they evolve it later?