The first people to reach the Americas came from Siberia, now in Russia, in a single group around 23,000 years ago, at the height of the last Ice Age, says a new study.
After reaching Alaska, they apparently hung out in the north - perhaps for thousands of years - before spreading throughout North and South America, said the study based on genomic analysis.
The findings dispel the popular idea that Polynesians or Europeans contributed to the genetic heritage of Native Americans.
The study revealed that the the first people to reach the Americas used a land bridge between Siberia and Alaska called Beringia.
"There is some uncertainty in the dates of the migration and the divergence between the northern and southern Amerindian populations. But as we get more ancient genomes sequenced, we will be able to put more precise dates on the times of migration," said one of the study authors Yun Song, associate professor at University of California, Berkeley.
The analysis, using the most comprehensive genetic data set from Native Americans to date, was conducted using three different statistical models.
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The data consisted of the sequenced genomes of 31 living Native Americans, Siberians and people from around the Pacific Ocean, and the genomes of 23 ancient individuals from North and South America, spanning a time between 200 and 6,000 years ago.
The international team concluded that the northern and southern Native American populations diverged between 11,500 and 14,500 years ago.
The southern branch peopled Central and South America as well as part of northern North America. The findings will be presented in the forthcoming issue of the journal Science.
"The diversification of modern Native Americans appears to have started around 13,000 years ago when the first unique Native American culture appears in the archaeological record: the Clovis culture," said Rasmus Nielsen, a professor at the California university.
"We can date this split so precisely in part because we previously have analysed the 12,600-year-old remains of a boy associated with the Clovis culture," Nielsen added.