Unprecedented feat reveals little-known Denisovans resembled Neanderthals but had ‘super-wide’ skulls
Source: The Guardian
One of the most mysterious relatives in the human family has stepped out of the shadows after scientists used ancient DNA from a fossilised finger to reconstruct their appearance.
The unprecedented feat, described as “exciting” and “extraordinary” by one leading researcher who was not involved in the work, shows that the Denisovans looked similar to the Neanderthals, but had wider heads and more protruding jaws.
“We expected them to resemble Neanderthals more than modern humans and this is what we found,” said Liran Carmel, a researcher on the team at the Hebrew University of Jerusalem. “But what fascinated us most is where the Denisovans differed from these other human groups.
“This might shed light on many of the questions that people have about the Denisovans, including how they adapted to their environment, and how the genetic traces they’ve left in modern humans might have helped them adapt to theirs.”
The Denisovans are thought to have lived across much of Asia tens of thousands of years ago, but until now almost nothing was known about their appearance.
The population first came to light in 2010 when part of a fossilised finger bone was unearthed in the Denisova cave in Siberia’s Altai mountains. A few other remnants have been found since then, including three large teeth and lower jaw bone.
The smattering of remnants paint a partial picture of the mysterious individuals. Genetic tests show that the Denisovans were close relatives of Neanderthals, and that our ancestors bred with them on occasion, perhaps as recently as 15,000 years ago. The prehistoric partnerships left modern Melanesians and indigenous Australians with up to 6% Denisovan DNA, with lesser amounts found in east Asians, Native Americans and Polynesians.
Carmel and his colleague David Gokhman came up with an ingenious approach to infer what the Denisovans looked like. They began by analysing what is called DNA “methylation” in Denisovans, neanderthals and modern humans. Methylation is a natural process that tags genes with a chemical marker. The markers operate a bit like volume switches, turning a gene’s activity up or down.
By comparing “methylation maps” of the three ancient human populations, the researchers worked out which Denisovan genes were as active as those in modern humans or Neanderthals, and crucially which were expressed very differently.
Armed with the list of genes, the researchers next consulted a huge medical database that links human genetic disorders, including skeletal problems, to glitches in the activity of particular genes. From this they worked out how gene activity patterns in the Denisovans would affect their appearance.
Gokhman and Carmel identified 56 parts of the Denisovan anatomy that differed from modern humans or Neanderthals, 34 of which affected the Denisovan skull. While the Denisovans had wide pelvises like the neanderthals, the analysis published in Cell shows they had wider skulls and longer dental arches, or jaws, making room for their larger teeth.
“Perhaps most surprising was their super-wide skulls, wider than modern humans’ and neanderthals’, who already have wide skulls,” said Gokhman. The finding adds weight to suspicions that a mystery human skull recently unearthed in Xuchang, China, also belonged to a Denisovan.
Highlighting what made the Denisovans unique will help scientists understand how they adapted to the conditions they lived in and what role their genes play in people alive today, said Gokhman.
While the technique is not good enough to give scientists accurate new measurements for the Denisovans, that may become more possible in the future. “All of this information is in our DNA, we just need to learn how to read it, and given how fast genetics is evolving, I don’t think it’s going to take very long,” said Gokhman.
David Reich, a Harvard geneticist who has worked extensively on ancient human DNA, said: “This is a highly original and exciting study, which is extraordinary not just with respect to the specific findings but also with respect to the entire approach.”
Asked whether DNA might one day help police reconstruct the faces of wanted persons, Gokhman added: “It’s a very exciting direction, but we are way too far at this point. Our approach is a step in this direction, but just a step.”