Fossils around 150,000 years old have finally given a face to a human population that long remained mysterious.
Denisovans are close cousins of Neanderthals and our own species. We already knew they existed thanks to DNA extracted from a few remains discovered in Asia. But researchers had too few securely identified bones to know what they looked like.
Geographic locations, original fossils and virtual reconstructions.
In China, the Xujiayao site yielded fragments of skulls, teeth and a jawbone. They are between 199,000 and 138,000 years old. Since their discovery, these fossils have raised a question: which branch of the human family did they belong to?
An international team found the answer by studying proteins preserved in two bones. These molecules, which make up our tissues among other things, can leave traces long after DNA has disappeared. Certain differences in their composition make it possible to identify relationships between ancient populations.
The scientists recovered 18 ancient proteins. One of them, collagen, bore a feature previously observed in Denisovans, but not in Neanderthals or modern humans. For the researchers, this is very strong evidence: the Xujiayao fossils belong to the Denisovan lineage.
Profile of the Harbin skull, a human fossil discovered in northeastern China and linked to the Denisovans.
Illustration: Clumsystiggy, via Wikimedia Commons.
The significance goes far beyond this identification. Unlike the first known remains of these humans, the Xujiayao bones make it possible to reconstruct a large part of a skull. The researchers compared them with other fossils from Asia, including the Harbin skull, which has also been linked to the Denisovans.
The emerging portrait is that of humans with relatively low skulls, thick bones and pronounced brow ridges. Their faces were relatively flat, without a jaw projecting far forward. There were nevertheless differences between individuals, and not all these features were necessarily present in each one.
The study also leads scientists to propose a new identification for several other Chinese fossils. Their similarities could indicate that they belonged to the same lineage. This part of their work is nevertheless based on comparing bones, without molecular evidence for each fossil.
These ancient proteins can now link bones to a known population and provide a much more concrete idea of what these vanished cousins looked like.