Paris: In the "Out of Africa" theory, Homo sapiens left their ancestral home in east Africa around 50,000 years ago, heading north, west and south.
Their East Asian descendants eventually crossed from Siberia to Alaska, island-hopping across the frozen Bering Strait, around 15,000 years ago.
Thus began human settlement of modern-day North America, according to this thinking.
But a new study suggests this human odyssey is rather more complex, and just as compelling.
Against all expectations, DNA teased from the bones of a child who lived in Siberia 24,000 years ago shows that the forerunners of Native Americans can also be traced to Western Eurasia.
The evidence comes from "MA-1", whose bones were found in Mal`ta in south-central Siberia in the 1920s and are today stored at the Hermitage Museum in Saint Petersburg.
A tiny sample of DNA -- just 0.15 grammes (0.005 of an ounce) -- from the mitochondria and nucleus of cells found the signatures of dual ancestry: one relating to modern-day East Asians and the other to modern-day West Eurasians.
The result was confirmed by a second Siberian sample that was 17,000 years old.
Around 14-38 percent of Native American ancestry today may have originated from humans who came from Western Eurasia, according to the study, published in the journal Nature.
The discovery suggests that human migration was more complex than thought -- Homo sapiens` thrust northwards also appears to have headed much farther eastwards than thought.
It also may explain why several skulls of First Americans, in previous research, are described as having features that do not resemble those of East Asians.
"The result came as a complete surprise to us," said Eske Willerslev, a professor at the Centre for GeoGenetics in Denmark, who led the probe.
"Who would have thought that present-day Native Americans, who we learned in school derive from East Asians, share recent evolutionary history with Western Eurasians?"