Genomic analysis suggests the original founding Americans migrated from Siberia across an ancient land bridge, coming in a single wave no more than 23,000 years ago, researchers say.
They likely remained in the north for many thousands of years before heading south to become two distinct populations in North and South America, they say.
The findings, based on the most comprehensive genetic data set from Native Americans ever gathered, confirms the most popular theory of how the Americas were populated, that of a single founding migration, the researchers suggest in their study set to appear in the journal Science.
A number of theories on how many migratory waves may have crossed that land bridge and when has made the subject of the populating of the Americas a controversial one.
A number of genetic studies, including the latest analysis, have connected both ancient and modern humans in the Americas to ancestral populations in Eurasia.
From that initial migration 23,000 years ago, the ancestral Americans began splitting into two distinct branches around 13,000 years ago when retreating glaciers opened migratory routes into the interior of North America.
Those two groups became what anthropologists identify as Amerindians -- American Indians -- and Athabascans, a people native to Alaska.
Some previous studies had suggested ancestors of those two groups had crossed over the Siberian land bridge, but the new work suggests otherwise, researchers say.
"Our study presents the most comprehensive picture of the genetic prehistory of the Americas to date," says Maanasa Raghavan, a lead author on the work. "We show that all Native Americans, including the major sub-groups of Amerindians and Athabascans, descend from the same migration wave into the Americas."
Still, other studies have raised some new questions, and possible suggestions of more than one founding population.
Writing in the journal Nature, researchers from Harvard University report finding DNA evidence of a vanished "ghost population" in the Amazon region of South America.
Members of two Amazonian groups, the Suruí and the Karitiana, are more closely related to Papua New Guineans and Aboriginal Australians, they say.
Distant ancestors of Australasians may have also crossed the land bridge, only to be replaced by the First Americans in most of North and South America, they argue.
"We think this is an ancestry that no longer exists in Asia, which crossed [the] Beringia [land bridge] at some point, but has been overwritten by later events," says David Reich, a population geneticist at Harvard Medical School.
Whether this ghost population arrived before, after or at the same time as the wave of Eurasian migrants remains unclear, the researchers say.
One thing is clear, they acknowledge; there's a lot more research that needs doing.
"There is a greater diversity of Native American founding populations than previously thought," says Harvard geneticist Pontus Skoglund. "And these founding populations connect indigenous groups in far apart places of the world."
