Nearly one-third of Native American genes come from west Eurasian people linked to the Middle East and Europe, rather than entirely from East Asians as previously thought, according to a newly sequenced genome.

Based on the arm bone of a 24,000-year-old Siberian youth, the research could uncover new origins for America's indigenous peoples, as well as stir up fresh debate on Native American identities, experts say.

The study authors believe the new study could also help resolve some long-standing puzzles on the peopling of the New World, which include genetic oddities and archaeological inconsistencies. (Explore an atlas of the human journey.)

"These results were a great surprise to us," said study co-author and ancient-DNA specialist Eske Willerslev, of the University of Copenhagen, Denmark.

"I hadn't expected anything like this. A genome related to present-day western Eurasian populations and modern Native Americans as well was really puzzling in the beginning. How could this happen?"

So what's new?

The arm bone of a three-year-old boy from the Mal'ta site near the shores of Lake Baikal in south-central Siberia (map) yielded what may be the oldest genome of modern humans ever sequenced.

DNA from the remains revealed genes found today in western Eurasians in the Middle East and Europe, as well as other aspects unique to Native Americans, but no evidence of any relation to modern East Asians. (Related: "Is This Russian Landscape the Birthplace of Native Americans?")

A second individual genome sequenced from material found at the site and dated to 17,000 years ago revealed a similar genetic structure.

It also provided evidence that humans occupied this region of Siberia throughout the entire brutally cold period of the Last Glacial Maximum, which ended about 13,000 years ago.

Why is it important?

Prevailing theories suggest that Native Americans are descended from a group of East Asians who crossed the Bering Sea via a land bridge perhaps 16,500 years ago, though some sites may evidence an earlier arrival. (See "Siberian, Native American Languages Linked—A First [2008].")

"This study changes this idea because it shows that a significant minority of Native American ancestry actually derives not from East Asia but from a people related to present-day western Eurasians," Willerslev said.

"It's approximately one-third of the genome, and that is a lot," he added. "So in that regard I think it's changing quite a bit of the history."

While the land bridge still formed the gateway to America, the study now portrays Native Americans as a group derived from the meeting of two different populations, one ancestral to East Asians and the other related to western Eurasians, explained Willerslev, whose research was published in the November 20 edition of the journal Nature.

"The meeting of those two groups is what formed Native Americans as we know them." (Learn more about National Geographic's Genographic Project.)

What does this mean?

Willerslev believes the discovery provides simpler and more likely explanations to long-standing controversies related to the peopling of the Americas.

"Although we know that North Americans are related to East Asians, it's striking that no contemporary East Asian populations really resemble Native Americans," he said.

"It's not like you can say that they are really closely related to Japanese, Chinese, or Koreans, so there seems to be something missing. But this result makes a lot of sense regarding why they don't fit so well genetically with contemporary East Asians—because one-third of their genome is derived from another population."

The findings could also allow reinterpretation of archaeological and anthropological evidence, like the famed Kennewick Man, whose remains don't look much like modern-day Native American or East Asian populations, according to some interpretations.

"Maybe, if he looks like something else, it's because a third of his ancestry isn't coming from East Asia but from something like the western Eurasians." (Read about history's great migration mysteries.)

What's next?

Many questions remain unanswered, including where and when the mixing of west Eurasian and East Asian populations occurred.

"It could have been somewhere in Siberia or potentially in the New World," Willerslev said.

"I think it's much more likely that it occurred in the Old World. But the only way to address that question would be to sequence more ancient skeletons of Native Americans and also Siberians."

Intriguing questions also exist about the nature of the advanced Upper Paleolithic Mal'ta society that now appears to figure in Native American genomes.

The Siberian child "was found buried with all kinds of cultural items, including Venus figurines, which have been found from Lake Baikal west all the way to Europe.