This is the first time scientists have been able to recreate the physiognomy of this hominid species – but the study has been questioned by other experts.
By Guilherme Eler
Sep 20, 2019, 20:26
The first evidence of the existence of Denisovans, cousins of Homo sapiens extinct 30,000 years ago, were found only in 2008. The archaeological material that has gathered from these hominids has since been confined to three teeth, a jaw (discovered May 2019) and a piece of bone from a finger.
It was from this last trace that researchers were able to access the DNA of these distant ancestors – and for the first time to draw up a spoken portrait of them.
"Denisovans resemble Neanderthals in many ways, but in some ways they look like us and in others they are totally unique," said Liran Carmel, one of the researchers who signs the study, in a statement.
The research, which involved scientists from Israel and Spain, identified 56 aspects in which denisovans differ from modern humans or Neanderthals. 34 of these differences are in the skull: the denisovan skull box is wider than the other two groups.
Instead of guiding the reconstitution work from sequencing DNA samples, the researchers used a different technique. In the study, the factor that weighed the most was not the letter sequence (A, T, C, G) that forms the genetic code – but how active or inactive certain portions of DNA were. Calm down, we explain.
The "activity" in question is defined by small modifications in DNA – called methylations. The word methylation has to do with a chemical group named methyl, nothing but three hydrogen atoms around one carbon atom. Such methyl, when switching places, is able to "shut down" pieces of the genome, and generate genetic changes without altering the appearance of the letter sequence – the recipe for genetic cake that ensures that each cell will perform a specific function.
Scientists collected data on methylation denisovan fossil, two 50,000-year-old Neanderthals and five H. sapiens who lived between 45,000 and 7,500 years.
The next step was to compare the methylation patterns of denisovan bone extracted DNA with the way methylation influences the skeletal formation of the two relatives of denisovans that are still alive today: humans and chimpanzees.
The work, then, was to try to imagine how these differences could influence the shape of a denisovan's body (and bones). All based on how the methylations had turned genes on or off in humans and chimpanzees.
The result was up to 85% accurate, scientists estimate, and this is what you see in the picture above. The woman in question is believed to have lived in what is today Siberia around 50,000 years ago. As it is a more general reconstruction, the figure represents a group of individuals, not a specific Denisovan. But you can identify in the model some unique features, such as the most pronounced dental arch – in addition to the elongated face and the large pelvis bone. These traits bring them closer to Neanderthals than to primitive humans, something already known to science.
There is evidence that both Neanderthals and Denisovans have coexisted with primitive humans for thousands of years. More than that, they even shared a cave in Siberia and related sexually – which proves that humans share a certain percentage of their genome with Denisovans.
Despite having achieved an unprecedented feat, the study was not unanimous among the scientific community. Some researchers have questioned whether the method used would have made too many approximations – distancing the final aspect of Denisova's real appearance from the man.
"Although the result sounds quite convincing, it really isn't," said John Hawks, a University of Wisconsin professor interviewed by New Scientist magazine. "Studying methylation differences is a promising field of research, but we still have a long way to go to understand how methylation differences can imply skeletal changes."
The scientific study was published in Cell magazine.