You, me, and every person on Earth are the last surviving members of a genus called Homo. But we weren’t always the only humans on the planet.
Neanderthals and Denisovans, two “archaic humans” that are now extinct, were so closely related to our species that these three groups interbred within the last 40,000 years. But while you might have a mental picture of a Neanderthal, it’s trickier to imagine a Denisovan.
That’s because scientists have found hundreds of Neanderthal fossils, including many skulls, which have informed visual reconstructions of these archaic humans. Denisovans, in contrast, are known from only a handful of fossils: a finger bone, a jaw, and some teeth.
Despite the limitations of the fossil record, scientists have managed to create mesmerizing new portraits and anatomical sketches of Denisovans using DNA extracted from the rare bones they left behind. The results were published on Thursday in the journal Cell.
"We provide the first reconstruction of the skeletal anatomy of Denisovans," said study author Liran Carmel, a geneticist at 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."
For instance, Denisovans likely had a wider skull than either modern humans or Neanderthals, as well as a longer dental arch.
Carmel and his colleagues were able to recreate these physical details by focusing on a process called DNA methylation. Methylation occurs when a methyl compound, which is a type of methane-derived compound, is attached to a DNA molecule. This addition does not change the DNA sequence, but it can influence how that gene is expressed.
The team compared methylation patterns found in DNA from chimpanzees, Neanderthals, and Denisovans, and predicted how the differences in gene expression between each species would affect their anatomy. When they modeled visualizations of chimpanzees and Neanderthals, the results were 85 percent accurate, which gave the scientists confidence that the Denisovan visualization would closely resemble this enigmatic extinct relative.
"Studying Denisovan anatomy can teach us about human adaptation, evolutionary constraints, development, gene-environment interactions, and disease dynamics," Carmel said. "At a more general level, this work is a step towards being able to infer an individual's anatomy based on their DNA."