More than a thousand years ago, the Vikings arrived on the world stage as swiftly as their longships cut through the waves. They raided and traded, conquered and colonized. They left their mark on four continents — not just at archaeological sites, but also in the flora and fauna, the languages and local populations.
The Viking Age did not last long — it’s generally defined as beginning in the late eighth century and ending in most areas by the early 12th century — but the explorers still capture our imagination today.
“The Vikings epitomized the freedom and strength we like in our heroes,” says Judith Jesch, professor of Viking studies at the University of Nottingham. “They were enterprising and bold; they were certainly violent, but so was everyone else at the time — and still are.”
But despite their well-documented spirit of adventure, warrior culture and innovative shipbuilding, the Vikings still have their secrets. Questions remain about how they lived, where they traveled and who they really were.
Now, like ship captains setting sail to untouched shores, scientists are exploring a new age of Viking research. On this adventure, DNA is their map.
Genetic studies have made stunning claims recently, ranging from who’s buried in a famous Viking grave to just how far across the Atlantic Ocean the Vikings may have traveled. Even more research is underway, though results may disappoint anyone expecting tidy answers.
“Viking is not a genetic term,” says University of Bergen geneticist Ellen Røyrvik, who was part of a landmark 2015 genetic study of populations in the British Isles. “It’s a cultural and historical label we’ve given them.”
There was also no single Viking identity. Viking Age populations from Denmark, Norway and Sweden each had different genetic signatures. As Vikings settled Iceland, or mixed with populations in Ireland, the British Isles and beyond, those genetic patterns evolved. Untangling the different threads can be difficult and open to numerous interpretations.
DNA can, however, give us details we would otherwise never learn. For example, in contrast to well-known boat burials, in which high-status individuals were laid to rest in a hull with lavish grave goods, animals and even slaves, “DNA can give you a picture of more average people, who wouldn’t have been able to afford the richest burials,” says Røyrvik. “It can provide a real cross section of a population.
“But you won’t get as much as people want from DNA,” she cautions. “All it does is give you someone’s biological identity.” And even that can raise more questions than it answers.
Last September, researchers publishing a study in the American Journal of Physical Anthropology thought they were putting to rest a decades-old question about the individual buried in one of the most famous Viking Age graves. They had no idea that, on the contrary, they were reigniting a debate that quickly grew to a firestorm.
The grave at the heart of the controversy is known academically as Bj 581. It’s in Birka, one of Sweden’s greatest Viking Age archaeological sites: In addition to being a trading center, the town saw more than 3,000 burials. Bj 581 in particular stands out. Unearthed in the late 19th century, the grave held remains of a single human, two horses, a mini-arsenal of weaponry and other warrior goods.
The original excavators assumed that the individual who’d been buried armed to the teeth was a man. In the 1970s, however, archaeologists re-examining the remains noted that certain anatomical features, including the shape of the pelvis, suggested the skeleton belonged to a woman. Such osteological analysis is not always conclusive, and the claim stirred up controversy over whether the Viking warrior ranks included women.
To resolve the matter, Charlotte Hedenstierna-Jonson, an archaeologist now at Uppsala University, and colleagues analyzed ancient DNA from Bj 581’s remains. The results, published in the 2017 paper, were conclusive: Bj 581 was female.
In addition to determining her sex, however, the study went a step further — and a step too far, say critics, who spoke out via online forums and social media, often anonymously. Many took exception with the study’s published title: “A female Viking warrior confirmed by genomics.” All genomics had really confirmed, charged skeptics, was that Bj 581 was female — and, some added, one buried without physiological hints of being a warrior, such as healed battle wounds or the thickening of bone associated with intense physical activity, like years of swinging a sword or ax.
Uppsala University archaeologist Neil Price, a co-author of the study, reacted to the critics with a mix of irritation and disbelief. “This particular grave has long been held up as the type-example of a high-status male warrior,” Price noted via email. “So the fact that the body is actually female has obvious implications, not least in undermining assumptions.”
Price added: “One of the most important qualities of a good researcher is the willingness to be wrong, but critique has to be constructive and it has to be informed, which was unfortunately not the case with much of what was posted on social media.”
One of the critics to weigh in without anonymity was the University of Nottingham’s Jesch, who took exception to the results in part because some of her previous research was cited — and, she says, misrepresented — in the paper.
“Because I deal with ‘just’ words and sometimes pictures, scientists don’t think the work is as rigorous as theirs,” says Jesch, adding that, as someone who studies languages and literature, she follows scientists’ work but doesn’t count herself among them.
“These scientific advances are very exciting,” she says, “and shed light on the past, but you are doing historical inquiry; you need to include archaeology and the study of language and texts. The geneticists wouldn’t even be asking these questions if archaeologists and historians hadn’t already considered them.”
The continuing controversy over Bj 581 illustrates a larger issue for DNA-driven research: how to resolve contradictions between results of genomic research and evidence from more traditional disciplines.
Beginning in the ninth century and continuing for much of the Viking Age, a large swath of what’s now England was under the Danelaw: the rule of the Danes, specifically Danish Vikings. Even today, Colby, Skeyton and dozens of other English villages have place names derived from Old Norse.
In 2015 in Nature, researchers published results from the People of the British Isles (PoBI) project, which sought to map the modern population’s genetic makeup in unprecedented fine scale. The project had collected genetic samples from more than 2,000 people living in the same rural areas that their grandparents had called home. The idea was to collect DNA from geographically stable populations to find clusters of genetic similarities that predated the post-Industrial Revolution world of heightened mobility. And the team did find 17 of these clusters.
Most of the paper’s conclusions were not surprising, but one became a lightning rod: There was no obvious genetic evidence of Danish occupation, suggesting “relatively limited” Danish Viking influence. For many archaeologists and historians, the finding seemed to flout their extensive research documenting a substantial and long-term Danish Viking presence, in the Danelaw area and beyond.
In late 2016, University of Bergen geneticist Røyrvik, one of the authors of the 2015 Nature study, took the unusual step of publishing a different interpretation of her own paper. “When you write a paper with 15 different people, not everyone’s perspective can be included,” Røyrvik says.
The response, published in Antiquity and co-authored with Oxford University archaeologist Jane Kershaw, offered an “alternate interpretation” of the PoBI data regarding Danish Vikings — one that integrated archaeological evidence as well as historical and linguistic clues. For example, Kershaw and Røyrvik noted the scores of Viking Age brooches unearthed in rural England. These brooches were more than family heirlooms or status-associated jewelry: They were basic wardrobe necessities, worn daily to keep a woman’s outer, apron-like dress from falling off. The number of brooches found points to whole families, not just an occupying force, present across the area.
Røyrvik stresses that she stands by the bulk of the Nature paper. “On the basis of one sentence being incorrect, it doesn’t mean the entire paper is incorrect,” she says. The story behind the 2015 paper’s conclusions about Danish influence provides a cautionary tale of how DNA-based studies of historical populations can go awry.
The trouble began when researchers sought non-British populations to compare with their samples. “We collected a lot of very well-sourced samples from British people,” Røyrvik says. “Quite late in the day, the comparison with European populations was done. We tried to get funding but the EU didn’t go for it.”
Without the European Union’s financial support, the team pulled together data from previous studies, some of them with a very different focus. Danish genetic signatures, for example, came from the DNA of multiple sclerosis patients at a Copenhagen hospital who had participated in an earlier MS study. There was no genetic material from a control population of healthy Danes, nor was there any information about the patients’ hometowns.
“It wasn’t ideal. It was the endpoint of a lot of different processes,” Røyrvik says.
The lack of carefully sourced modern Danish DNA meant that the Danish genetic signature was not as well-defined as it would have been had the researchers sampled a population in Denmark with the same methodology they used for participants in Britain. It may seem like splitting hairs, but without a clear Danish signal, it was much harder to separate Danish Viking patterns from those of another northern European population present in Britain: Just a few hundred years before the Vikings, Anglo-Saxons from northern Germany had landed in England, and many had settled.
“There is an overlap of geography, and they’re also very close temporally,” Røyrvik says of the two northern European groups. She believes that genetic signatures interpreted as Anglo-Saxon in the Nature paper may have been at least partly from Danish Vikings.
“With any given scientific paper, you hope the data is correct, and ours was excellent. You hope the analysis of the data is correct, and I believe ours was. The interpretation is the issue,” Røyrvik says.
The Littlest Vikings
While unraveling the genomes of the Vikings and their descendants makes headlines, a humbler source of DNA is providing some of the most intriguing clues to their lost history. Just ask Cornell University’s Jeremy Searle, an evolutionary biologist whose team uses small mammals — particularly mice — to track historical human movement.
Because it’s especially difficult to obtain ancient mouse DNA — genetic matter in the small bones degrades faster than in that of larger animals, and there’s often not enough left to sample — Searle and his team compare the DNA from modern, geographically diverse mice. Much of their work focuses on the house mouse (Mus musculus), which evolved to be commensal with humans: The mice are not domesticated like dogs or sheep, but they are dependent on living in and around a human settlement.
Searle’s Viking research began with a startling discovery more than a decade ago, while helping a student analyze mouse DNA from the Portuguese island of Madeira, more than 400 miles off the coast of Morocco. Searle was initially comparing the genetic signatures of the Madeira sample with other mouse DNA by hand, a slow and painstaking process that has since been largely replaced by computer programs.
“I expected [the Madeira mouse DNA] would match with sequences from Portugal — Madeira was discovered by the Portuguese, colonized by the Portuguese, and the bulk of movement via ports was with Portugal,” says Searle. “When I compared the sequences by eye, they didn’t link up with Iberia at all, but were identical to northern Europe.”
Further analysis, including ancient DNA sequencing published by a second team in 2014, confirmed a strong link in the genetic signatures of Madeira mice with mice that lived among Danish Viking Age populations. Although there is no archaeological or historical record of the Vikings landing on Madeira, Searle believes one of their ships may have been blown off course, ending up on the remote Atlantic island. The Vikings’ stay on the island was apparently brief, just long enough for a few stowaway rodents to take some shore leave that ended up being permanent.
Similar research since has found what may be the genetic signatures of Norwegian Viking Age mice in modern populations on the Azores, an island chain more than 900 miles west of Portugal.
Mice, says Searle, make particularly good surrogates, or bioproxies, for human movement. “Apart from humans and some domestics that humans brought with them, mice are the most globally distributed mammals,” he says. “They reproduce quickly and can get onto vehicles and boats. And when you’re trying to understand human history and movement, you’re talking about boats and caravans.”
Despite the occasional unintentional global hitchhiking, mice are relative homebodies. They generally stay within a territory of a few hundred feet, so they’re unlikely to colonize new areas unless human movement takes them there.
“Mice were accidentally dropped, left like a pottery shard,” says Searle. “But unlike a pottery shard, these living artifacts have DNA, which is an extraordinary encyclopedia of information that you can now use in a very sophisticated way.”
And using mice as bioproxies can tell us not only where the Vikings traveled, but also how many of them occupied a place. Says Searle: “Where you have more people, you’re likely going to have more mice.”
The Viking Cods
University of Oslo evolutionary biologist Sanne Boessenkool and her botanist colleague Anneleen Kool are three years into exploring a question that flips Searle’s research on its head.
“We’re not using plants and animals to figure out where the Vikings went,” says Boessenkool. “We’re using where the Vikings went to find out what they did with the plants and animals.”
At the outset of their multiyear project, Kool and Boessenkool planned to base their research exclusively on ancient flora and fauna DNA samples from museum collections and some fresh excavations. But all ancient DNA is prone to degradation and contamination from both microbes in the environment and modern human handling — and ancient plant DNA is even more fragile.
“We wondered, are we going to get any DNA?” recalls Boessenkool. “The answer was no.”
Instead of abandoning the Viking flora project altogether, Kool is now working with linguists to use plant names as a kind of substitute for DNA to trace the spread of their use, and how that use evolved.
Their work on ancient DNA from Viking Age horses is more promising: Kool and Boessenkool have collected about 100 samples, in different states of preservation, from which they hope to build a detailed picture of how equine populations moved and changed.
“We have no idea what story will be told, but we’re going to have a good data set to tell it with,” says Boessenkool.
University of Oslo biologist Bastiaan Star relied on ancient DNA from a different animal to chart Viking ingenuity in a 2017 PNAS study. Through genetic material preserved in fish bones from archaeological sites, Star and colleagues uncovered the apparent origin of a trade route that continues today.
The team’s research showed that Vikings initially caught cod in the arctic waters off Norway’s Lofoten Islands, whose climate allows for preservation through air drying, rather than more expensive salting. After preservation, the fish were then shipped south for consumption in Germany and elsewhere.
“The Vikings were very smart about their surroundings,” says Star. “They went to the Lofotens because they knew there was a massive cod spawn and they could dry the fish without salt, making it an extremely cheap protein. They used their environment to its maximum potential.”
Aside from the occasional academic skirmish and setbacks due to DNA degradation, genomic-driven studies of the Viking Age are gathering momentum and, promisingly, are including more input from other disciplines.
“We can sequence DNA, but without knowing the stories, the context, it’s meaningless,” says Boessenkool. She notes that, despite DNA’s popular image of objective precision, the data often requires interpretation, which is based on a researcher’s assumptions. “Sometimes the [genetic] signals are very clear, but sometimes they’re not.”
She adds: “The geneticists publish the DNA data, but too often they don’t actually listen to what the archaeologists are saying. We’re very aware of that, and trying not to be that way. But also, we’re biologists. We’re from different worlds [than the archaeologists] and speak a different language.”
The current body of DNA-derived research on the Vikings is just the tip of the spear. Uppsala archaeologist Price is two years into a decade-long, $6 million project to reveal the economic, social and environmental factors that led to the Viking Age.
Paleogeneticist Eske Willerslev, who gained fame for using ancient DNA to revise our understanding of First Americans, is working on a separate project involving genetic material from the Viking Age.
Willerslev’s team declined to comment ahead of any published work, but among the expected early results: a DNA-based study of multiple men found buried in two Scandinavian boats on the Estonian coast. The boats, excavated between 2008 and 2012, have been dated to the mid-eighth century and are from the Late Vendel Period, the Viking Age precursor.
Excavation head and Tallinn University archaeologist Jüri Peets hopes DNA will determine kinship between the men, which could provide another clue to how the Viking Age evolved.
As Uppsala University’s Hedenstierna-Jonson, lead author of the controversial Bj 581 study, explains, “We need as many pieces as we can get to get closer to the actual truth, although I don’t believe we will ever be able to know everything. After all, it’s all about people and they were — and are — wonderfully complex and unpredictable.”