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Nearly 11,000 years ago, a man died in present-day Nevada. Wrapped in a blanket of rabbit skin and reed mats, he was buried in a place called Spirit Cave.
Now scientists have recovered and analyzed his DNA, as well as that of 70 other ancient peoples whose remains have been discovered throughout the Americas. The results bring astonishing details to a story once lost to prehistory: how and when humans spread in the Western Hemisphere.
Research suggests that the first known Asian immigrants were already divided into distinct groups. Some of these populations have flourished and become the ancestors of indigenous peoples from all over the hemisphere.
But other groups have completely disappeared, leaving no trace, if this is what can be discerned in the old DNA. Indeed, new genetic research suggests many dramatic chapters of the Americas population that archeology has not yet discovered.
"This is essential for archaeologists," said Ben Potter of the University of Alaska, who did not participate in the drafting of the new documents. "Holy cow, that's great."
Previous studies had shown that people had moved to the Americas at the end of the last ice age, traveling from Siberia to Alaska via a land bridge that was now under the Bering Sea. They spread to the south, eventually reaching the tip of South America.
Until recently, geneticists could hardly give information on these vast migrations. Five years ago, only one ancient human genome was found in the Western Hemisphere: that of a 4,000-year-old man discovered in Greenland.
The last batch of analyzes, published in three separate studies, marks a turnaround. In recent years, researchers have retrieved the genomes of 229 old people from teeth and bones found throughout the Americas.
The first, described in January by Eske Willerslev, a geneticist at the University of Copenhagen, was an 11,500-year-old girl whose human remains were discovered in eastern Alaska.
The second was discovered hundreds of miles away, in western Alaska, and lived 9,000 years ago, Dr. Willerslev and his colleagues reported in the journal Science.
Separated Beringian elders ancestors of the living indigenous peoples of the Americas about 20,000 years ago. The new findings suggest that they lasted for thousands of years. Then they disappeared, leaving no known genetic trace in living people.
But another wave of migrants Siberia did not stop in Alaska. They continued to advance, finally arriving south of the glacial glaciers. Then they split into two branches.
One group turned around and headed north after glacier retreat in Canada and then back to Alaska. The other branch made a remarkable trip to the south.
Genetic data suggest that this group quickly spread to much of North and South America about 14,000 years ago. The expansion may have taken only centuries.
"It's basically an explosion," said Dr. Willerslev.
The man from Spirit Cave in Nevada belonged to this so-called southern branch of migrants. Mr. Willerslev also discovered that he was close to a 12,700-year-old boy discovered on the other side of Montana's Rocky Mountains.
But the Spirit Cave man also proved to have a close genetic link with 10,400-year-old skeletons discovered 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.
"We agree that he must act quickly," said Dr. Reich.
From about 9,000 years ago, both teams discovered that new waves of people have moved south. Willerslev's research suggests that newcomers mingle with older populations in South America.
Mr. Reich, for his part, sees evidence of two waves of migrants who have completely replaced the people who lived in South America.
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The new research also revealed cases of remarkable continuity, kinship ties extending over thousands of years.
Willerslev and his colleagues compared Spirit Cave's human genome to four sets of remains found near the cave in Lovelock, Nevada, which lived 600 years ago.
All these people were closely In return, his team has found, although it is separated by 10,000 years of history.
A similar link has been found in the Andes. John Lindo of Emory University and his colleagues analyzed the DNA of seven people who lived at altitude between 6,800 and 1,400 years ago.
Researchers estimate that people living above 7,500 feet in the mountains were separated from lowland populations between 9,200 and 8,200 years ago. Today, mountaineers still show a strong genetic link with the ancient remains.
"This is not something you see in most other parts of the world," said Dr. Reich.
In 2015, Dr. Reich and his colleagues discovered that some people living in the Amazon had a DNA very similar to that of people currently living in Australia and New Guinea.
The researchers speculated that their ancestors included an unknown group, which scientists called Population Y, who separated separately to the Americas.
In their new study, Dr. Reich and his colleagues found no trace of the Y population – but Dr. Willerslev's team was able to identify their DNA in some of Brazil's 10,400-year-old skeletons.
"The million dollar question is obviously, how did this happen?" Said Dr. Willerslev.
Perhaps another group of Asians entered the Americas long before the ancestors of the Spirit Cave man and other ancient Native Americans. They may have crossed with Amazonians before disappearing completely.
Or maybe some of the early members of the South Branch have had some strange genes that have survived through the generations.
The new wave of genetic samples reflects the improved relationship between scientists and indigenous peoples. For decades, many tribes have rejected requests for DNA from researchers.
The man from Spirit Cave, for example, was dug up by archaeologists in 1940 and stored in a museum. The local tribe, the Fallon Paiute-Shoshone, only learned of the body's existence in 1996. For years, she fought for her repatriation.
"It's totally disrespectful," said Rochanne L. Downs, a member of the tribe's cultural committee. "If someone entered the Arlington Cemetery and dug the grave of one of the soldiers and took his medals, there would be contempt."
Initially, the tribe opposed the search for DNA in the skeleton, because scientists should destroy a large part of it. Dr. Willerslev met with the tribe and explained to him that he would only need a tooth and a small bones.
The tribe has agreed to give him a chance to find DNA in the remnants of the cave in mind.
Willerslev's results led the Bureau of Land Management to hand over the skeleton to the tribe. Last year, they buried the Spirit Cave man in a secret location.
Ms. Downs will not rule out similar studies in the future, but said that each application would require careful consideration.
"Everything will be on a case-by-case basis," she said. "The essential is our respect for the remains."
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