Northern and southern Native American populations diverged between 11,500 and 14,500 years ago …
FRISCO — Scientists say they’re a lot closer to pinpointing how and when the first Native Americans came to the Americas, and how they spread across two continents.
The findings came from a detailed analysis of genetic material from 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 study shows that the original Americans came from Siberia in a single wave no more than 23,000 years ago, at the height of the last Ice Age, and apparently remained in the north, perhaps for thousands of years, before spreading in two distinct populations throughout North and South America.
The study confirms the most widely accepted theory of how Native Americans arrived and shoots down some other concepts, including the idea of an earlier wave of arrivals that predated the last glacial maximum. The findings also don’t support the idea that multiple independent waves produced the major subgroups of Native Americans we see today, as opposed to diversification in the Americas.
The 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 Artic beginning about 5,500 years ago.
The findings also dispel the idea that Polynesians or Europeans contributed to the genetic heritage of Native Americans.
“There is some uncertainty in the dates of the migration and the divergence between the norther and southern Amerindian populations,” said Yun Song, a UC Berkeley associate professor of statistics and of electrical engineering and computer sciences. “But as we get more ancient genomes sequenced, we will be able to put more precise dates on the times of migration.”
The international 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 Rasmus Nielsen, a UC Berkeley professor of integrative biology. “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.”