CORVALLIS, Ore. - A single wave of migration from Siberia brought people across the Bering Land Bridge and into the Americas no more than 23,000 years ago, with the group later splitting into two branches, a new study of ancient and modern genetic information has found.
Using genetic data from ancient and modern sources, researchers found that the ancestors of present-day Native Americans entered the Americas in one initial wave and then divided into two groups, known as Athabascans and Amerindians about 13,000 years ago.
The results were published this week in the journal Science.
The findings also indicate that the initial migration of Native American ancestors likely followed a route along the Pacific coast as they spread into the Americas. The northern branch, which included Amerindians as well as Athabascans, remained only in North America, while the southern branch, made up only of Amerindians, spread along the Pacific Rim through North and South America.
Researchers say the findings, which match closely with archaeological evidence from the period, clearly answer a much-debated question about how and when the Americas were first populated and counters ideas that migration to the Americas initially occurred in two waves.
"This means the Paleo American model is essentially dead," said Loren Davis, an associate professor of anthropology in the College of Liberal Arts at Oregon State University and co-author on the study. "There was no founding population that was replaced by a later influx of Native Americans. Nearly all native peoples in the Americas can trace their genetics to that first wave of migration."
"It's really exciting because these findings provide new archaeological implications for us to explore."
The genetic study was led by Maanasa Raghavan and Eske Willerslev of the Centre for GeoGenetics at the University of Copenhagen in Denmark.
To determine the origins of today's Native American people, researchers sequenced genomes from present-day individuals from the Americas, Siberia and Oceania and compared their genetics to those from ancient specimens from both branches of the migration.
Davis worked with the research geneticists to identify skeletons from northwestern Mexico that were tested as part of the study. The unusual skull shape of some of the skeletons was one factor that led some researchers to believe there were two waves of migration to the Americas, he said.
"Now we're seeing that the metrics of skulls matters less than the genetics," Davis said. "Our study shows that the skeletal morphology of ancient Americans doesn't indicate the presence of different genetic populations unrelated to modern Native Americans."
With the new findings in hand, Davis is looking at new avenues of archaeological research, including searching for evidence of when and how the original group of migrants split. One source of information is the types of stone tools used by the two groups, he said. There are two known traditions of tool-making that separate the two groups: the Western-Stemmed and Clovis Paleoindian traditions. The two technological traditions use different strategies to create stone tools, Davis said.
"The two genetic groups became the basic nexus for all the later Native American people," Davis said. "This split between the two tool-making technologies may have been happening at the same time the two groups divided."
Davis' next project involves looking offshore for sites that may once have been home to early settlers in North America. Such sites were likely submerged in the post-Ice Age sea rise. Working with the Bureau of Ocean Energy Management, Davis developed a predictive model to identify the potential distribution of archaeological sites submerged along the coast of the United States, in part by reconstructing the landscape and ancient river drainages that once existed during times of lower sea levels. In September, he and others will begin working offshore to find those sites.
"The implications of this study are significant for the archaeological problems I'm pursuing," Davis said. "The study's conclusion that the initial migration of Native American ancestors probably followed a Pacific coastal route of entry meant that we're on the right track to make significant discoveries here in the Pacific Northwest."
Click photos to see a full-size version. Right click and save image to download.
Loren Davis, 541-250-6304, email@example.com