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While there’s only one species of human still alive today, we share our genus with a number of ancient hominins. The most famous is probably the Neanderthals, but in 2010, scientists discovered a mystery finger bone fragment in Siberia’s Denisova Cave. This newly discovered group of archaic humans are known as the Denisovans and now, for the first time, we have an idea of what they might have looked like.
About 100,000 years ago, our ancestors lived alongside Neanderthals and Denisovans. In fact, they interbred with them, so most of us modern humans still bear some Denisovan DNA. But what did these archaic humans look like? All we have of the Denisovans is three teeth, a lower jaw bone, a couple of skull fragments, and the finger bone fragment found in Siberia. But that’s apparently enough to reconstruct a Denisovan face.
Reporting in the journal Cell, scientists used patterns of methylation in Denisovan DNA to build a picture of their facial features. They managed to identify 56 anatomical features that would have differed from those of modern humans and/or Neanderthals, 34 of which affected the skull. For example, the Denisovans likely had the widest faces of the three hominins.
"We provide the first reconstruction of the skeletal anatomy of Denisovans," said Liran Carmel, of the Hebrew University of Jerusalem, in a statement. "In many ways, Denisovans resembled Neanderthals, but in some traits, they resembled us, and in others they were unique."
To come to their conclusions, the researchers looked at patterns of gene activity influenced by DNA methylation and epigenetics rather than the DNA sequence itself. These processes affect gene activity without altering the base sequence of DNA. The researchers searched for differences between DNA methylation in modern humans, Neanderthals, and Denisovans and tried to determine how these differences might affect physical appearance. They worked this out using what we know about various human disorders in which these genes stop functioning properly.
"By doing so, we can get a prediction as to what skeletal parts are affected by differential regulation of each gene and in what direction that skeletal part would change – for example, a longer or shorter femur," explained first author David Gokhman.
The researchers found that Denisovans probably had elongated faces and wide hips like the Neanderthals did, but had increased dental arches (the crescent arrangements of teeth in the mouth) and particularly wide faces.
To check that their methodology wasn’t completely missing the mark, the researchers tested it out on chimps and Neanderthals because we already know what they look like. When it came to reconstructing these hominins, the team managed to determine traits with 85 percent accuracy, suggesting that their technique for determining the Denisovan face isn’t perfect but works pretty well. In fact, while their paper was being peer-reviewed, a study describing the first confirmed Denisovan jawbone was released, and it matched up with what the team had estimated.
"Studying Denisovan anatomy can teach us about human adaptation, evolutionary constraints, development, gene-environment interactions, and disease dynamics," explained Carmel. "At a more general level, this work is a step towards being able to infer an individual's anatomy based on their DNA."
