Scientists have managed to link Native Americans living in the Amazon to indigenous people in Australasia. The findings may hint at a previously unknown wave of migration to the Americas thousands of years ago.

"It's incredibly surprising," said David Reich, one of the researchers, in a news release. "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."

Previous research had shown that Native Americans from the Arctic to the southern tip of South America can trace their ancestry to a single "founding population" called the First Americans. This group came across the Bering land bridge about 15,000 years ago.

In this latest study, the researchers looked at genetic data gathered as part of the 2012 study when he noticed a strange similarity between one or two Native American groups in Brazil and indigenous groups in Australia, New Guinea and the Andaman Islands.

"That was an unexpected and somewhat confusing result," said Reich. "We spent a really long time trying to make this result go away and it just got stronger."

The researchers found that the people of the Amazon had a genetic ancestor more closely related to indigenous Australasians than to any other present-day population. This ancestor doesn't appear to have left measureable traces in other Native American groups in South, Central or North America. In fact, the researchers believe that the ancestry is perhaps as old as the First Americans.

"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," said Reich.

The findings are published in the journal Nature.

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