To this date, we have no idea what a Denisovan looked like. You can still hold every known Denisovan fossil—that pinky, a toe, and two teeth—in your hand. But we know so much else about them. We know every letter of their genome. We know that they diverged from their close relatives, the Neanderthals, around 400,000 years ago, and that both groups diverged from Homo sapiens around 600,000 years ago. We know that when our ancestors left Africa and spread into Asia, they encountered the Denisovans and had sex with them. We know that, as a result, Denisovan DNA lives on in people from Asia and Melanesia. One of these Denisovan genes provides modern Tibetans with a crucial adaptation that allows them to survive at high altitudes. [...]
In the genomes of people from Japan and China, Browning found several segments that closely match the genome of the Denisovan woman whose pinky was found in the Altai Mountains. But to her surprise, she also found segments that were clearly Denisovan in origin, but were much weaker matches to the Altai female. “They’re close enough that we’re sure they’re Denisovan, but they’re not as close,” she says.
This suggests that modern humans inherited DNA from two separate groups of Denisovans. The way Browning sees it, the ancestors of today’s Melanesians encountered Denisovans as they expanded through South Asia and the Malay Peninsula. The two groups intrebred, with the result that 5 percent of modern Melanesian DNA has a Denisovan origin.
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