Did Neanderthals and our fully modern ancestors, the Cro-Magnons, have sex? This seemingly trivial question has engrossed scientists for generations. Until last week, the prevailing view held that Neanderthals and moderns never interbred. Now a highly respected group of geneticists has compared the Neanderthal genome with the complete genomes of five living humans from different parts of the world. To their astonishment, they found that Europeans and Asians share 1 to 4% of their nuclear DNA with Neanderthals, but Africans do not. In other words, some Neanderthals and moderns interbred after the latter left tropical Africa some 100,000 years ago, but before Homo sapiens arrived in Europe over 50,000 years later.

         “In a sense, the Neanderthals are not then altogether extinct,” says paleogeneticist Svante Paabo. If he is right, how and when did this interbreeding occur? Most likely, it transpired in the Middle East, perhaps some 80,000 years ago, known to us from caves, which contain skeletons of people who look partially modern and partly Neanderthal. Whatever happened, it was on a small scale, and nothing like swapping wives from cave to cave. The sex involved tiny numbers of people, perhaps Neanderthals who came in close juxtaposition with modern hunters by chance.  But why didn’t such interbreeding occur more often? Perhaps there were cultural barriers—feelings of repugnance and distrust, intellectual chasms caused by the vast cognitive chasm between Neanderthals and moderns—we will never know and can only speculate. But whatever happened, there is a little Neanderthal in many Europeans, among them this author, a relic of archaic people who lived alongside moderns and became extinct some 30,000 years ago. At least we can now move on from a preoccupation with ancient sex to a more nuanced study of the relationships between Neanderthals and their successors.