Scientists may have discovered a previously overlooked wave of migration to the Americas from Australasia that occurred thousands of years ago.
A team of researchers was surprised to find a genetic connection between Native Americans living in the Amazon and indigenous people in Australasia, indicating an ancient and dramatic migration, Harvard University Medical School reported.
"It's incredibly surprising," said David Reich, Harvard Medical School professor of genetics and senior author of the study. "There's a strong working model in archaeology and genetics, of which I have been a proponent, that most Native Americans today extend from a single pulse of expansion south of the ice sheets-and that's wrong. We missed something very important in the original data."
Past research has suggested Native Americans from the Arctic to the southern tip of South America can trace their lineage back to a "founding population" called the First Americans, who traveled across the Bering land bridge about 15,000 years ago.
Pontus Skoglund, first author of the paper and a postdoctoral researcher in the Reich lab, was the first to notice a genetic similarity between Native American groups in Brazil and indigenous groups in Australia, New Guinea and the Andaman Islands.
"That was an unexpected and somewhat confusing result," Reich said. "We spent a really long time trying to make this result go away and it just got stronger."
The researchers looked at genetic information from 21 Native populations from Central and South America as well as from nine populations in Brazil and about 200 non-American populations. The findings revealed the Tupí-speaking Suruí and Karitiana and the Ge-speaking Xavante of the Amazon had an ancestor that was more closely related to indigenous Australasians than any other modern population. The ancestor was dubbed "Population Y," and is believed to be as old as the First Americans.
"About 2 percent of the ancestry of Amazonians today comes from this Australasian lineage that's not present in the same way elsewhere in the Americas," Reich said.
In the future, the researchers may work to determine how much of the Amazonian's ancestry comes from Population Y, possibly through the study of ancient skeletons. They also hope to gain insight into what occurred after the migration, and how relationships between different groups developed.
"We have a broad view of the deep origins of Native American ancestry, but within that diversity we know very little about the history of how those populations relate to each other," Reich concluded.
The findings were published in a recent edition of the journal Nature.
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