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From the sequence data, they found gene variants indicating that the man had dark skin and eyes. He also had about 1% more Neandertal DNA than do Europeans and Asians today, confirming what another, even older human from Siberia had shown—that humans and Neandertals mixed early, before 45,000 years ago, perhaps in the Middle East.

The man from Kostenki shared close ancestry with hunter-gatherers in Europe—as well as with the early farmers, suggesting that his ancestors interbred with members of the same Middle Eastern population who later turned into farmers and came to Europe themselves. Finally, he also carried the signature of western Asians ...

Willerslev says the data suggest the following scenario: After modern humans spread out of Africa about 60,000 years ago, they encountered Neandertals and interbred with them, perhaps in the Middle East. Then while one branch headed east toward Melanesia and Australia, another branch of this founder population (sometimes called "basal Eurasians") spread north and west into Europe and central Asia. "There was a really large met-population that probably stretched all the way from the Middle East into Europe and into Eurasia," [evolutionary biologist Eske] Willerslev says. These people interbred at the edges of their separate populations, keeping the entire complex network interconnected—and so giving the ancient Kostenki man genes from three different groups. "In principle, you just have sex with your neighbor and they have it with their next neighbor—you don't need to have these armies of people moving around to spread the genes."

Later, this large population was pushed back toward Europe as later waves of settlers, such as the ancestors of the Han Chinese, moved into eastern Asia. The Kostenki man does not share DNA with eastern Asians, who gave rise to Paleoindians in the Americas.

But even if the man from Kostenki in Russia had all these elements 36,000 years ago, that doesn’t mean that other Europeans did, Reich says. His team’s DNA data and models suggest that Europeans in the west and north did not pick up DNA from the steppes until much later. He and Krause also think that Willerslev’s study needs to be confirmed with higher resolution sequencing to rule out contamination, and to have more population genetics modeling explain the distribution of these genetic types. The bottom line, researchers agree, is that European origins are “seem to be much more complex than most people thought,” Willerslev says.