COPENHAGEN — As a boy growing up in Denmark, Eske Willerslev could not wait to leave Gentofte, his suburban hometown. As soon as he was old enough, he would strike out for the Arctic wilderness.
His twin brother, Rane, shared his obsession. On vacations, they retreated to the woods to teach themselves survival skills. Their first journey would be to Siberia, the Willerslev twins decided. They would make contact with a mysterious group of people called the Yukaghir, who supposedly lived on nothing but elk and moose.
When the Willerslev twins reached 18, they made good on their promise. They were soon paddling a canoe up remote Siberian rivers.
“Nobody knew what you would see on the other side of a mountain,” said Eske Willerslev, who is now 44. “There were villages on the maps, and you wouldn’t even see a trace of them.”
Dr. Willerslev spent much of the next four years in Siberia, hunting moose, traveling across empty tundra and meeting the Yukaghirs and other people of the region. The experience left him wondering about the history of ethnic groups, about how people spread across the planet.
A quarter of a century later, Dr. Willerslev is still asking those questions, but now he’s getting some eye-opening answers.
As the director of the Center for GeoGenetics at the University of Copenhagen, Dr. Willerslev uses ancient DNA to reconstruct the past 50,000 years of human history. The findings have enriched our understanding of prehistory, shedding light on human development with evidence that can’t be found in pottery shards or studies of living cultures.
Dr. Willerslev led the first successful sequencing of an ancient human genome, that of a 4,000-year-old Greenlander. His research on a 24,000-year-old Siberian skeleton revealed an unexpected connection between Europeans and Native Americans.
Dr. Willerslev was one of the early pioneers of the study of ancient DNA, and today he remains at the forefront of an increasingly competitive field. His colleagues credit his success to his relentless work and to his skill at building international networks of collaborators.
“His role is that of catalyst, choreographer, conductor and cajoler — and sometimes all at once,” said David J. Meltzer, an archaeologist at Southern Methodist University.
The scientific enterprise that Dr. Willerslev helped invent now sometimes crosses into culturally sensitive terrain. Last June, he and his colleagues published the genome of an 8,500-year-old skeleton from Washington State known as Kennewick Man, or the Ancient One.
Native American tribes and scientists fought over control of the bones since their discovery in 1996. During his research, Dr. Willerslev met with representatives from the tribes. One tribe agreed to donate DNA for his study.
Kennewick Man, Dr. Willerslev and his colleagues concluded, was related to living Native Americans. That finding led to a momentous announcement last month: The Army Corps of Engineers said it would formally consider the request from the tribes to reclaim the skeleton and bury it.
Rane Willerslev, now a cultural anthropologist at the University of Aarhus, sees his brother’s work as a continuation of their Siberian adventure.
“He just became the kind of scientist he should have become,” Rane Willerslev said. “Anything else would have been wrong.”
It was on their third journey through Siberia, in 1993, that the Willerslev brothers finally found the Yukaghirs. An old man, covered in scars from hunting bears in his youth, led them to a Yukaghir village.
“It was completely different from what I imagined,” Dr. Willerslev said.
The Yukaghir were not an exotic tribe living in utter isolation. In fact, virtually all of them could count Russians and people from other ethnic groups among their ancestors. The Willerslev twins could find only a single old man who still spoke the native language.
That encounter was fresh in his mind when, back in Denmark, Dr. Willerslev learned that some scientists were extracting DNA from fossil mummies, a technique that might help explain the history of people like the Yukaghir.
But there was no one in Denmark doing that research, so one of Dr. Willerslev’s professors suggested a Plan B. They could investigate ancient ice that climate researchers at the University of Copenhagen had brought back from Greenland.
Dr. Willerslev and a fellow graduate student, Anders J. Hansen, set up a room where they could search for DNA in the ice cores. And in ice as old as 4,000 years, Dr. Willerslev and Dr. Hansen discovered DNA from 57 species of fungi, plants, algae and other organisms, dating back as far as 4,000 years.
The results were so remarkable for the mid-1990s that NASA called the young doctoral student to ask about his methods.
“I got completely convinced that I wanted to become a scientist,” Dr. Willerslev said. “There’s a big difference between reading about what others have discovered and discovering something yourself.”
After publishing the ice study in 1999, Dr. Willerslev emailed Russian scientists, who sent him sugar-cube-size chunks of permafrost from Siberia to search for ice age DNA.
In the very first cube, Dr. Willerslev hit genetic pay dirt. “You just saw woolly mammoth, reindeer, lemming, bison,” he said. “It was just incredible.”
Discovering a whole ice age ecosystem in a pinch of frozen dirt helped Dr. Willerslev earn a professorship at the university. He went on to found the Center for GeoGenetics, which now employs more than 100 scientists.
From the start, Dr. Willerslev made finding ancient human DNA one of the center’s top priorities. In 2006, he set out for northern Greenland with colleagues in hopes of finding some.
The scientists searched for animal bones that showed signs of being butchered. They hoped that the hunters might have left behind some of their DNA.
For more than a month, the scientists hacked into the ground, wearing full bodysuits to avoid contaminating the samples. But when they returned to Copenhagen and studied the bones, they were disappointed to find only animal DNA.
Not long afterward, Dr. Willerslev discovered that the trip had been unnecessary.
In the 1980s, university researchers had found a 4,000-year-old clump of hair in Greenland that had been stored — and forgotten — in a basement. “It was completely ridiculous,” Dr. Willerslev said.
Dr. Willerslev and his colleagues extracted DNA from the hair and used powerful new methods to reconstruct the genome of the Greenlander. It was the first time scientists had recovered an entire ancient human genome.
The hair turned out to belong to a man. His blood type was A positive, and he had a genetic predisposition for baldness. But most interesting of all, his genes contained clues about the history of Greenland and the Inuit who live there today.
“We could see these guys were not the direct ancestors of Inuit people,” Dr. Willerslev said. Instead, the ancient Greenlander belonged to a different group known as Paleo-Eskimos.
Analyzing the ancient genome, Dr. Willerslev and his colleagues concluded that Paleo-Eskimos migrated from Siberia about 5,500 years ago and endured for centuries in Canada and Greenland before vanishing. The Paleo-Eskimos were not the ancestors of today’s Inuits: They were replaced by them.
In the six years since that report, Willerslev and his colleagues have published a series of studies that have fundamentally changed how we think about human history.
Our species evolved in Africa about 200,000 years ago. Scientists are still working out how humans later populated the other continents. A lot of evidence indicates that Native Americans originated from a population somewhere in Asia more than 15,000 years ago. In search of clues to that founding population, Dr. Willerslev and his colleagues examined a 24,000-year-old bone buried near a village called Mal’ta in eastern Siberia.
In a preliminary study, Maanasa Raghavan, a researcher at the genetics center, discovered some DNA in the remains. But the genes seemed to belong to a northern European, not an East Asian.
“I put it on hold because I thought it was completely contaminated,” Dr. Willerslev said of the research.
After he and his colleagues developed more powerful methods for analyzing DNA, Dr. Raghavan and her colleagues returned to the Mal’ta DNA. It was not contaminated: Instead, it was a genome unlike anything they expected.
Parts of the boy’s genome closely resembled the DNA of ancient Europeans, but more of it resembled that of Native Americans.
“It was really an eye-opener,” Dr. Willerslev said. “This individual has nothing to do with East Asians. He has something to do with Europeans and Native Americans.”
It appears that the Mal’ta boy belonged to an ancient population spread out across Asia 24,000 years ago. They came into contact with an East Asian population at some point, and members of the two groups had children together. Native Americans are the descendants of those children.
The Mal’ta people are not related to the Asians who live in the region today. But before they disappeared, they also passed down their DNA to Europeans. Later research revealed the route those genes took from Asia to Europe.
In a study published last June, Dr. Willerslev and his colleagues discovered Mal’ta-like DNA in Bronze Age nomads called the Yamnaya, who lived 4,300 to 5,500 years ago in what is now southwestern Russia. About 5,000 years ago, the Yamnaya expanded into Europe, where they added their DNA to the gene pool.
The new research has prompted Dr. Willerslev to give up his earlier belief that the major groups of people in different parts of the world had largely separate genetic histories. “These results made it clear this simplified picture is not the truth,” he said.
In 2011, Dr. Willerslev and his colleagues made history once again by publishing the first genome of an aboriginal Australian. The research gave him new insights about human history.
But it also taught Dr. Willerslev a lesson about the ethics involved in studying ancient DNA.
Archaeological evidence shows that humans arrived in Australia at least 50,000 years ago. Scientists have long wondered if the aboriginals on the continent today are descendants of those first settlers, or of later arrivals.
Dr. Willerslev saw a weakness in early genetic studies on aboriginal Australians: Many aboriginals alive today have some European ancestry. He decided to look for an aboriginal genome free of European DNA.
In 2010, he found a piece of hair collected in Australia in the 1920s at the University of Cambridge. He and his colleagues retrieved DNA from the hair and reconstructed the owner’s genome.
Their analysis revealed that the ancestors of aboriginal Australians split off from other non-Africans about 70,000 years ago. That finding supports the idea that the first settlers in Australia were the ancestors of today’s aboriginals.
Dr. Willerslev was eager to share the new finding. But one of Dr. Willerslev’s co-authors, Rasmus Nielsen of the University of California, Berkeley, declared that they had made a grave mistake by not getting the consent of living aboriginal Australians.
“It didn’t seem right to circumvent the wishes of the aboriginal community by using that sample,” Dr. Nielsen said. “I was about to remove myself from the study due to these concerns.”
At first, Dr. Willerslev didn’t understand the fuss. “My view was that human history belongs to all of us because we’re all connected, and no people have a right to stop our understanding of human history,” he said.
But Dr. Willerslev decided to travel to Australia to meet with aboriginal representatives. He was shaken to learn of the unethical history of scientific research on aboriginal Australians.
Victorian anatomists plundered burial grounds, for example, and carried off bones to put in museums. Years of such exploitation had left many aboriginal Australians suspicious of scientists.
Today, geneticists who want to study aboriginal DNA need to obtain consent not just from donors, but from community organizations. And in many cases, there are limits on how widely scientific results can be shared.
“Paying attention now, I could see why they had this skepticism and resistance,” Dr. Willerslev said. “In retrospect, I should have definitely approached those people before undertaking the study. Just because it’s legally right doesn’t make it ethically right.”
In Australia, Dr. Willerslev met with the Goldfields Land and Sea Council, which represents aboriginal people in the region where the hair sample had been obtained. He described the results of his analysis and asked for the council’s consent to publish them.
The council gave him permission. In fact, when the study came out, they praised the results. “Aboriginal people feel exonerated in showing the broader community that they are by far the oldest continuous civilization in the world,” the council said in a statement.
His experiences in Australia have changed the way Dr. Willerslev and his colleagues investigate DNA from indigenous people. “I’ve evolved,” he said.
In 2011, he learned of a 12,700-year-old skeleton of a baby that had been found in 1968 on the Montana ranch of Melvyn and Helen Anzick. Dr. Willerslev got in touch with the family and received permission to search the bones of the so-called Anzick child for DNA.
Dr. Willerslev was aware that many Native Americans, like aboriginal Australians, have grown suspicious about being exploited by scientists. During the course of his research, he tried to make connections with the local tribes.
He contacted the Montana Burial Preservation Board, which protects Native American remains in the state. But the board told him he didn’t need their oversight because the bones were found on private land.
Dr. Willerslev and his colleagues succeeded in getting DNA out of the bones. Based on his research in Greenland, he had suspected that the child belonged to a vanished population with no close kinship to living Native Americans.
But the genome proved otherwise: The child was closely related to living Native Americans.
As the preliminary results emerged, Dr. Willerslev was introduced to Shane Doyle, a member of the Crow Tribe who was then a graduate student at Montana State University. Dr. Doyle took Dr. Willerslev to a series of meetings with tribal representatives.
Many of the people there were interested by the results. But many also told them that the Anzick child skeleton, like other remains found in Montana, deserved a proper burial.
“Their priority was to get the remains back of the ancestors and to re-inter them,” said Francis L. Auld, who was then the program manager of the tribal historic preservation office for the Confederate Salish and Kootenai Tribes.
With tribal representatives in attendance, the Anzick family buried the remains in June 2014, four months after the genome paper was published.
“It was a complicated case, and it would have been complicated for anyone,” said Dennis H. O’Rourke, a geneticist at the University of Kansas who was not involved in the research.
He said it would have been best if Dr. Willerslev and his colleagues had been able to confer with the tribes before doing the research. “But I was pleased to see that it was ultimately done,” he said.
Dr. Willerslev was then invited to look for DNA in one of the most controversial skeletons ever found: Kennewick Man.
In 1996, Ripan Mahli, then a graduate student, had tried to find DNA in the newly discovered remains. The methods at the time were too crude for the job, and research on Kennewick Man soon came to a halt as local tribes went to court to claim the bones.
After a decade of lawsuits, a team of scientists won the right to study Kennewick Man, and in 2013, Dr. Willerslev was invited to try again to retrieve DNA from the bones, using his latest methods.
As he assembled a team of experts, Dr. Willerslev asked Dr. Mahli, now at the University of Illinois, if he’d join. At first Dr. Mahli was reluctant. He had spent years building better relationships between scientists and Native Americans. A study of Kennewick Man might weaken those links.
But Dr. Mahli decided to join the team when Dr. Willerslev began meeting with local tribes. “My mind changed when I realized Eske was engaging with these communities,” he said.
“He has been great through all of this,” Jackie M. Cook, the repatriation specialist for the Confederated Tribes of the Colville Reservation, said of Dr. Willerslev.
The Kennewick Man genome, like the Anzick child’s, revealed an ancient continuity between living Native Americans and the earliest people in the New World. After Dr. Willerslev and his colleagues published their results last year, John Novembre of the University of Chicago confirmed them at the request of the Army Corps of Engineers.
Dr. Willerslev has mixed feelings about the consequences of his research on Kennewick Man.
“I’m a scientist, and it means I regret that important material is getting reburied,” he said. “But when you find that these remains are genetically Native Americans, it’s not our call anymore.”
Since the Kennewick Man project, Dr. Willerslev has hosted visits from a number of Native American tribes to his laboratory in Copenhagen. His guests have helped him see how differently he, as a European, treats history than they do.
Dr. Willerslev once proudly showed off a collection of ancient Danish skulls to Native American visitors, only to find them upset by the sight.
“‘How can you treat your ancestors like that, so disrespectfully?” he recalls them asking.
In December, Dr. Willerslev hosted Dr. Doyle along with Ben Cloud and Frank Caplett, also members of the Crow Nation. Dr. Willerslev took them around the lab and proposed research he hoped the tribe would consider.
Dr. Willerslev would like to investigate the influence of genes on the high rate of diabetes in Native Americans, for example. He has started similar work in Australia.
Mr. Cloud said he was intrigued by the idea. “I have family members who were younger than I am who are gone because of this disease,” he said. “How come my family is dying?”
Dr. Willerslev also raised the possibility of studying Crow DNA to understand their history. Dr. Doyle said he doubted the tribe would be interested.
“We’ve had white people coming in and telling us things for a long time, and it’s never really impressed us much,” he said.
Dr. Willerslev accepts that kind of rejection as part of his work. “We have to respect that as scientists,” he said. “We don’t have to agree.”
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