Original Americans came from Siberia; study refutes ‘two founding populations’ theory

By  | 

A new study has suggested that original Americans came from Siberia some 23,000 years ago and has outright rejected the possibility of ‘two founding populations’.

Researchers have suggested based on genomic analysis that original Americans came from Siberia in a single wave at the height of the last Ice Age; possibly stayed in the north for several thousand years and then finally spread in two distinct populations throughout North and South America.

The study, published in Science, echoes previous theory of how a single population spread across the Americas, but outright rejects a recently published study that there were two different populations that formed the first Americans. The study rejects the idea that a now extinct population with relation to East Asia was also responsible for some of the subgroups of Native Americans we see today. The findings also dispel the idea that Polynesians or Europeans contributed to the genetic heritage of Native Americans.

This Ice Age migration over a land bridge between Siberia and Alaska is distinct from the arrival of the Inuit and Eskimo, who were latecomers, spreading throughout the Arctic beginning about 5,500 years ago.

Researchers used most comprehensive genetic data set from Native Americans to date for their analysis using three different statistical models, two of them created by UC Berkeley researchers. The first model takes into account the full DNA information available from the genomes in the study. A second method, developed by Rasmus Nielsen, a UC Berkeley professor of integrative biology, and graduate student Kelley Harris, requires much less computation, but relies on a summary of the genome data. These and a third method developed by researchers at the Wellcome Trust Sanger Institute, England, all yielded consistent results. Yun Song, a UC Berkeley associate professor of statistics and of electrical engineering and computer sciences, and Nielsen are two of three corresponding authors of the paper.

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 research team concluded that the northern and southern Native American populations diverged between 11,500 and 14,500 years ago, with the northern branch leading to the present day Athabascans and Amerindians broadly distributed throughout North America. The southern branch peopled Central and South America, as well as part of northern North America.

“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 archeological record: the Clovis culture,” said Nielsen. “We can date this split so precisely in part because we previously have analyzed the 12,600-year-old remains of a boy associated with the Clovis culture.”

One surprise in the genetic data is that both populations of Native Americans have a small admixture of genes from East Asians and Australo-Melanesians, including Papuans, Solomon Islanders and Southeast Asian hunter gatherers.

“It’s a surprising finding and it implies that New World populations were not completely isolated from the Old World after their initial migration,” said Eske Willerslev from the Centre for GeoGenetics at the Natural History Museum, University of Copenhagen, who headed the study. “We cannot say exactly how and when this gene flow happened, but one possibility is that it came through the Aleutian Islanders living off the coast of Alaska.”

Song added that the state-of-the-art statistical methods that his and Nielsen’s labs developed “are being made publicly available so that they can be used by others to study complex demographic histories of other populations.”