In the years that followed the discovery of Denisovans, scientists used DNA sequencing to attribute a few molar teeth from the cave to the same group4. They have also found other remains that harboured Neanderthal DNA. The analysis of Denny fills in some important details about the two groups. “We knew that Denisovans and Neanderthals had been there. We just didn’t think they interacted this intimately,” says [Svante] Pääbo. “It was so amazing to find direct proof — to find these people in the act, almost, of mixing.”The Denisova cave appears to have been occupied for several hundred thousand years, being originally settled by either Denisovans or Neandertals, no one is sure which. Subsequent to this, it is unclear how much interbreeding actually occurred.
Denny’s discovery has also convinced Pääbo and other scientists that the remains of similar individuals, with recent ancestry from two groups of hominin, will be found — perhaps also in Denisova Cave. Researchers who analysed Denny’s genome found signs that the chromosome set that was contributed by her father, although clearly Denisovan, harboured some Neanderthal ancestry, which hints at earlier encounters between the groups2. “We should be able to pick up these individuals,” says [Katerina] Douka.
“It’s still a head scratcher,” adds Tom Higham, an archaeological scientist at the University of Oxford, UK, who works with Douka and Brown. “It’s either an incredible piece of luck, or interbreeding happens so frequently that we might expect to find these types of occurrence in the archaeological record.”One thing becomes increasingly clear with each new discovery, however: the complete replacement model of modern human origins, as espoused by Stringer and Andrews, is dead.