image: Fig 4. Diversification within the Americas, based on the research by Raghavan et al. is shown. view more
Credit: [Credit: Raghavan et al., <em>Science</em> (2015)]
This news release is available in Japanese.
Using genetic data from ancient and modern individuals, researchers have provided one of the clearest pictures yet of how and when the ancestors of present-day Native Americans entered the Americas, suggesting they did so as a single wave - not in multiple waves, as some have thought. Deciphering how and when the Americas were first populated has been a challenge. Though it is generally accepted that ancestors of modern-day Native Americans descended from Siberians who crossed the Bering Land Bridge, the exact timing and pattern of entry is still debated; researchers dispute when ancestral Native Americans left Siberia, whether they came to the Americas in one wave or multiple (with multiple serving as a source of genetic diversity), and how long they spent isolated in the Bering Strait region before arriving, with one model suggesting 15,000 years. To help shed light on these questions, Maanasa Raghavan et al. sequenced and compared the genomes of ancient and modern individuals from the Americas, Siberia, and Oceania. Among results from a range of analyses that also leveraged previously published genomic datasets from Europe and Africa, the researchers estimate that ancestral Native Americans migrated from Siberia to the Americas no earlier than 23,000 years ago, during the harsh and frigid Last Glacial Maximum - and after no more than 8,000 years of isolation. They find no evidence for multiple waves of entry to the Americas, suggesting instead a single wave (thus implying present-day genetic differences among Native American populations arose not from multiple, diverse migration waves, but from events after migration). The results also suggest a common Siberian source population for Native Americans. Furthermore, the researchers' data show that ancestral Native Americans split off into two branches around 13,000 years ago, coinciding with glacier melt and the opening of routes into North America's interior. The two branches led to the diverse Native American populations seen today.
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Article #20: "Genomic evidence for the Pleistocene and recent population history of Native Americans," by M. Raghavan at Natural History Museum of Denmark in Copenhagen, Denmark, and colleagues. For a complete list of authors, see the manuscript.
Note: This paper will be available for free when the embargo lifts at http://www.sciencemag.org.
Journal
Science