Americans said to have two ‘founding’ populations


In contrast to previously established ancestry theory, a new study based on genomic analysis has traced American ancestry to two founding populations with a genetic connection to indigenous people in Australasia.

The latest study published in Nature puts forwards strong genetic proof that a previously unknown wave of migration to the Americas thousands of years ago acted as one of the founding populations of the Americas.

The genetic link between population in Americas and indigenous groups in Australia, New Guinea and the Andaman Islands came to light in 2012 during a study by Pontus Skoglund, first author of the new paper and a postdoctoral researcher at David Reich’s lab – a Harvard Medical School professor of genetics. Skoglund noticed a strange similarity between one or two Native American groups in Brazil and indigenous groups in Australasia.

This suggested that there could be a possibility of error in the initial data collection process or that certain indigenous groups in northern Canada inherited DNA from at least two subsequent waves of migration. To ensure that their observations were correct, Skoglund and colleagues from Harvard Medical School, the Broad and several universities in Brazil analyzed publicly available genetic information from 21 Native American populations from Central and South America.

Beyond that they also collected and analyzed DNA from nine additional populations in Brazil. The team then went on to compare genomes to the genomes of people from about 200 non-American populations. Surprisingly, the link persisted suggesting that there is something that researchers had missed for a long time.

“That was an unexpected and somewhat confusing result,” said Reich, who is also an associate member of the Broad Institute of Harvard and MIT and a Howard Hughes Medical Investigator. “We spent a really long time trying to make this result go away and it just got stronger.”

Researchers found that the Tupí-speaking Suruí and Karitiana and the Ge-speaking Xavante 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 measurable traces in other Native American groups in South, Central or North America.

The genetic markers from this ancestor don’t match any population known to have contributed ancestry to Native Americans, and the geographic pattern can’t be explained by post-Columbian European, African or Polynesian mixture with Native Americans, the authors said. They believe the ancestry is much older–perhaps as old as the First Americans.

Researchers however, reveal that this population – which they have named Population Y, after the Tupí word for ancestor, “Ypykuéra” – isn’t existent anymore. They carried out lot of sampling in East Asia and nobody looks like members of Population Y.

According to the new proposal put forward by Reich, Skoglund and colleagues, members of Population Y and first Americans came down from the ice sheets to become the two founding populations of the Americas. However, they haven’t been able to ascertain the order, time separation or geographical patterns.

Researchers do know that the DNA of First Americans looked similar to that of Native Americans today. Population Y is more of a mystery.

According to researchers, about 2 per cent of the ancestry of Amazonians today comes from this Australasian lineage that’s not present in the same way elsewhere in the Americas; however, that doesn’t given an conclusive evidence about how much of their ancestry comes from Population Y.

Reich and Skoglund think that some of the most interesting open questions about Native American population history are about the relationships among groups after the initial migrations.

“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.