Native Americans—and their genes—traveled back to Siberia, new genomes revealed Science

The remains of three people who died on a riverbank in the Kamchatka Peninsula in northeastern Siberia some 500 years ago have yielded a surprising secret: Their DNA shows they had some North American ancestry, according to a study published today. Considered alongside other ancient and modern genomes, the results suggest that although the ancestors of today’s Native Americans came from Asia, the passage was not one way. Instead, the Bering Sea region was a place of intercontinental connection, where people routinely boated back and forth for thousands of years.

“The idea of ​​back migration makes the history of this area a bit more complex, but also a bit more realistic,” says Anders Götherström, a geneticist at Stockholm University who was not involved in the work. “Humans have an amazing ability to get to places.”

Beginning about 20,000 years ago, people living in Siberia journeyed across the Bering Strait into Alaska and spread south through the Americas. Sea levels were much lower at the time, allowing hunter-gatherers to cross a frozen land bridge into the new continent or boat along its coast.

When the last ice age ended about 11,500 years ago and glaciers melted, the Bering Sea rose and divided the two continents. But migrants continued to arrive, mixing with and replacing earlier groups to shape the modern genetic landscape of Indigenous Americans. By 5000 years ago, people had settled across Alaska and northern Canada.

In 2019, researchers published work based on genetic and linguistic evidence suggesting that sometime between 2200 and 500 years ago, people living in northwestern Alaska boated back across the Bering Sea into Siberia. But it wasn’t clear whether this gene flow of Native American ancestry back into Asia was commonplace or a one-off.

Around the same time, Russian archaeologists excavating a site on the banks of the Kamchatka River found the remains of the three people. When an international team of scientists led by Cosimo Posth, a paleogeneticist at the University of Tübingen, extracted and analyzed DNA from the bones, the researchers found these people were closely related to modern-day Kamchatkan populations. Yet they also had genes that appeared to come from groups living in North America.

The researchers roughed out a family tree by comparing the trio’s genomes with those from modern populations and other ancient genomes from the region and across the Americas. The scenario that best explains their history involves people crossing from Alaska back into Siberia and mixing with populations there some 5000 years ago, and again about 1500 years ago, the researchers report today in Current Biology.

DNA sequenced from Altai hunter-gatherers sheds light on the genetic origins of Bronze Age groups across the Central Asian steppe.Artur L. Kungurov

“We’re not able to say how many times these gene flow events occurred over the past 5000 years,” Posth says. “What we’re trying to say is that it could have been multiple, repeated events, or it could have been gradual, constant, continuous. It’s difficult to say, but clearly… it was a prolonged event.”

“This idea of ​​backflow that’s happening not just once or twice, but occurring over a very long time scale—several thousands of years is very interesting,” says Vagheesh Narasimhan, an integrative biologist at the University of Texas, Austin. But he would like to see more evidence to back it up, from archeology as well as DNA. Götherström agrees that repeated backflow is the most likely scenario given the available evidence. But he and Posth agree it’s not possible to rule out the idea that the “Native American” genes—which the authors carefully refer to as “Native American–related ancestry”—come from an ancient group that never left Asia but that shares ancestry with Native Americans.

Other ancient genomes analyzed in the study underline that ancient Siberia was a human crossroads. Six came from the mountainous Altai region near/in Mongolia, dating to between 5500 and 7500 years ago. Five of these so-called Altai hunter-gatherers belonged to a population that apparently gave rise to several later peoples who spread throughout the Central Asian steppe during the Bronze Age. One of the six, buried with ritualistic items suggesting he may have been a shaman, had ancient Northeast Asian ancestry—the westernmost example of this lineage yet found. And a 7000-year-old individual found near Russia’s far eastern border with China appears to derive more than one-quarter of their ancestry from a group that lived on the Japanese archipelago called the Jōmon people. The Jōmon settled these islands some 30,000 years ago, but the genome suggests the islanders maintained at least some contact with mainland populations, Posth says.

“They’re really clearly showing there’s something Jōmon-like on the mainland,” says Melinda Yang, a geneticist at the University of Richmond who studies the genetic history of ancient East Asian populations. The paper is “fine-tuning” our understanding of how East Asian ancestry came to permeate Siberia during the Holocene.

“Each newly produced ancient human genome from the region continues to surprise us and to broaden our understanding … of the region’s dynamic population history,” agrees Gülşah Merve Kılınç, a paleogeneticist at Hacettepe University.

But additional evidence is unlikely to emerge anytime soon. Posth says his team’s collaboration with Russian colleagues began before Russia’s invasion of Ukraine, and all the samples analyzed in the study were exported before fighting broke out. Following up on the work, he says, is currently impossible: “Right now, everything is frozen. As frozen as the permafrost in Siberia.”

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