This eureka moment in human evolution stemmed from a single fragment of bone about 90,000 years old, found in 2012 in the Denisova Cave, which is a large limestone cavern in Siberia’s Altai mountains.  The tiny bit of bone turned out to belong to the teenage daughter of two different human species.

IHuman ancestors coexisted with at least three other hominins: Neanderthal, Denisovan, and the wee Homo floresiensise. All other species or groups of humans have gone extinct, as far as we know.

“We knew from previous studies that Neanderthals and Denisovans must have occasionally had children together,” says co-author Viviane Slon, researcher at the Max Planck Institute for Evolutionary Anthropology and co-author of the article. “But I never thought we would be so lucky as to find an actual offspring of the two groups.”

Which raises the question of whether finding the hybrid girl’s remains was incredible luck or a sign that our ancestors weren’t that fussy in their mating habits.

Some call that ‘species’

Neanderthals and ancient modern humans split about 530,000 years ago, according to current genetic estimates. Neanderthal ancestors probably migrated out of Africa after that time and settled in Eurasia, Slon says.

The bit of bone, by the way, was from one of the hybrid teenage girl’s long bones: but with no clear distinctive features, we can’t say if it was an arm or a leg.  We have enough bones to have some idea what Neanderthals looked like, but the fragments of  Denisovan bones only tell us that these cousins were large. All we have of Denisovans so far is four specimens: one finger and three teeth – plus this teenager’s long bone shard, all found in the Denisova Cave. For all we know, the two groups mixed because they couldn’t tell each other apart. Or care. Plus ça change, plus c’est la même chose?

Since the cave remains the only sure source of Denisovan remains, and since the highest concentration of their genes is in Melanesians, some think Denisovans once thronged Asia. Neanderthals lived throughout those parts of Europe not covered in ice, in Siberia and in the Levant. They seem to have spread east and west in temperate Europe. In any event, they clearly met in Siberia.

The earliest-known Denisovan in that Siberian cave lived at least 130,000 years ago. They are believed to have died out about 40,000 years ago.