The Denisovan contribution to modern humans is smaller in most populations — perhaps 0.1 to 0.5 percent in most Eurasians — but is significantly higher in populations from Oceania.

The ancestors of modern Papuans and Australian Aboriginal people carry between 3 and 6 percent Denisovan ancestry, a proportion that implies a substantial episode of interbreeding somewhere along the route from mainland Asia to the Pacific.

The picture that emerged from these genetic analyses was one of ancient humans as not quite distinct species in the conventional biological sense — or at least, not species that maintained absolute reproductive barriers between them.

They could and did interbreed.