Earliest Americans came from Asia in a rush, ancient DNA shows
Nearly 11,000 years ago, a man died in what is now Nevada. Wrapped in a rabbit-skin blanket and reed mats, he was buried in a place called Spirit Cave.
Now scientists have recovered and analyzed his DNA, along with that of 70 other ancient people whose remains were discovered throughout the Americas. The findings lend astonishing detail to a story once lost to prehistory: how and when humans spread across the Western Hemisphere.
The earliest known arrivals from Asia were already splitting into recognizably distinct groups, the research suggests. Some of these populations thrived, becoming the ancestors of indigenous peoples throughout the hemisphere.
But other groups died out entirely, leaving no trace save for what can be discerned in ancient
DNA. Indeed, the new genetic research hints at many dramatic chapters in the peopling of the Americas that archaeology has yet to uncover.
“Now, this is the grist for archaeologists,” said Ben Potter of the University of Alaska, who was not involved in the new papers. “Holy cow, this is awesome.”
Earlier studies had indicated that people moved into the Americas at the end of the last ice age, traveling from Siberia to Alaska across a land bridge now under the Bering Sea. They spread southward, eventually reaching the tip of South America.
Until recently, geneticists could offer little insight into these vast migrations. Five years ago, just one ancient human genome had been recovered in the Western Hemisphere: that of a 4,000-year-old man discovered in Greenland.
The latest batch of analyses, published in three separate studies this week, marks a turnaround. In the past few years, researchers have recovered the genomes of 229 ancient people from teeth and bones discovered throughout the Americas.
One of them is a rare individual, only the second so-called Ancient Beringian whose DNA has ever been analyzed.
The first, described in January by Eske Willerslev, a geneticist at the University of Copenhagen, was a 11,500-yearold girl whose remains were found in eastern Alaska.
The second was discovered hundreds of miles away, in western Alaska, and lived 9,000 years ago, Willerslev and his colleagues reported Thursday in the journal Science.
The Ancient Beringians separated from the ancestors of living indigenous people in the Americas about 20,000 years ago. The new findings suggest they endured for several thousand years. Then they disappeared, leaving no known genetic trace in living people.
But another wave of migrants from Siberia did not stop in Alaska. They kept moving, eventually arriving south of the ice age glaciers.
Then they split into two branches.
One group turned and headed north, following the retreating glaciers into Canada and back to Alaska. The other branch took a remarkable journey south.
The genetic data suggest that this group spread swiftly across much of North America and South America about 14,000 years ago. The expansion may have taken only centuries.
“It’s basically an explosion,” Willerslev said.
The man from Spirit Cave in Nevada belonged to this southern branch of migrants. He also was closely related to a 12,700-year-old boy found on the other side of the Rocky Mountains in Montana, Willerslev also found.
But the man from Spirit Cave also turned out to have a close genetic link to 10,400-year-old skeletons found in Brazil, on the other side of the equator.
David Reich of Harvard University and his colleagues found a similar pattern in their own research, published Thursday in the journal Cell.
They uncovered a link between the ancient Montana boy and another group of ancient South Americans, including a 10,900-year-old skeleton in Chile. Like Willerslev’s work, the kinship suggests that migrants moved quickly from North America to South America.
“We agree that this must be a rapid radiation,” Reich said.
Starting about 9,000 years ago, both teams found, additional waves of people moved southward. Willerslev’s research suggests the new arrivals mixed with older South American populations.
Reich, on the other hand, sees evidence for two waves of migrants who completely replaced the people who had lived in South America.
The new research also revealed instances of remarkable continuity, kinships that spanned thousands of years.
Willerslev and his colleagues compared the genome of the man from Spirit Cave to those of four sets of remains found nearby in Nevada’s Lovelock Cave, who lived as recently as 600 years ago.
All of these people were closely related, his team found, despite being separated by 10,000 years of history.
A similar bond was found in the Andes. John Lindo of Emory University and his colleagues analyzed DNA from seven people who lived at high elevations between 6,800 and 1,400 years ago.
The excavation of a skeleton about 9,600 years old in Brazil. New DNA analyses show the earliest known Americans split into groups after crossing from Asia.
Eske Willerslev, center, a geneticist at the University of Copenhagen, talks to members of the Fallon Paiute-shoshone tribe in Nevada. With permission from the tribe, Willerslev retrieved DNA from a tooth belonging to the Spirit Cave man.