An international study reveals that the ancestors of all present-day Native Americans arrived in the Americas as part of a single migration wave, approximately 23,000 years ago.

The research, published in the online edition of Science on July 21, was co-authored by Drs. Vaughan Grimes and Michael Deal of Memorial’s Department of Archaeology. Kelly-Anne Pike, an MA graduate of the department, is also listed as a co-author.

There is archaeological evidence of modern humans in the Americas by ca. 15,000 years ago (KYA). However, there is still debate over exactly when and how many times the ancestors of present-day Native Americans entered the New World from Siberia. A large genome-scale study, conducted by an international team headed by the Centre for GeoGenetics at the University of Copenhagen, reveals that the ancestors of all present-day Native Americans arrived in the Americas as part of a single migration wave, no earlier than 23 KYA.

Within the Americas, the ancestral Native American pool diversified into two basal branches around 13 KYA. The team also reports a later gene flow into some Native Americans from groups related to present-day East Asians and Australo-Melanesians. Finally, the results from this study show no support for certain historical Central and South American groups with distinctive cranial morphology being relicts of an early and separate migration into the Americas, as proposed by the Paleoamerican Model.

“The scale and scope of our study gives an unprecedented view into the population history of the New World, including North, Central and South America,” said Dr. Grimes. “It also provides a framework to carry out similar types of research using ancient genetics and archaeological data on a regional scale, which will allow for a more nuanced understanding of population continuity and/or change though time for the ancient and contemporary First Nations in these areas.”

In order to develop a more detailed account of when and how the Americas were peopled, the team generated genomic data from several present-day Native American and Siberian populations, which are poorly represented in the genetic literature. They also sequenced ancient samples from across the Americas, spanning ca. 6,000 - 200 years ago, to trace the genetic structure over time.

Since Amerindians and Athabascans were part of the same migration into the Americas, the current genetic differences observed between them would have emerged sometime after 23 KYA.

The team found evidence for a split in the ancestral Native American gene pool that lead to the formation of two distinct genetic branches, namely the “northern” and “southern” branches, and that this split occurred ca. 13 KYA. The “northern” branch was found to be present in northern North America and included both northern Amerindian groups as well as Athabascans. The “southern” branch, on the other hand, included Amerindians from southern North America and Central and South America.

When comparing the genetic affiliations of sequenced ancient samples from the Americas, the team found that several samples were genetically more closely related to modern-day populations from the same geographical location. This result indicates that there was a genetic and geographic continuity of Native American groups across the millennia in at least some parts of the Americas.

The study reports a signal of gene flow between some Native Americans and groups related to present-day East Asians and Australo-Melanesians, the latter including Papuans, Solomon Islanders and South East Asian hunter-gatherer groups. While the signal is weak, it presents an intriguing scenario of a distant Old World connection to Native Americans after their split from one another and after the latter had peopled the Americas.

The paper Genomic Evidence for the Pleistocene and Recent Population History of Native Americans was published online in Science July 21, 2015.