Viking DNA study finds they were more genetically diverse than modern Scandinavians

Modern humans like to think a lot of themselves — take globalization, for example. Modern folks would be forgiven for believing that with the ease of travel and the historical migration of peoples across the world, most populations have a more diverse genetic record than they did in their supposedly more isolated past. But a new study that traces Viking DNA through to modern Scandinavia suggests otherwise.

Some interactions between different groups of people leave a long-lasting mark on their descendants’ genes, like how people of European descent tend to carry tiny bits of Neanderthal DNA in their genomes.

Other times, though, the genetic record of ancient interactions fades over time. That seems to be what happened in the wake of the Viking Age in Scandinavia, which today comprises Denmark, Norway, and Sweden, according to a recent study. Paleogeneticist Ricardo Rodrı́guez-Varelal and his colleagues at Stockholm University and the Centre for Paleogenetics studied ancient DNA gathered from people buried at sites across Scandinavia going back 2,000 years. The researchers traced how the Scandinavian genome changed over time — and how immigrants to northern Europe influenced the gene pool.

The results were published Thursday in the journal Cell.

What’s New — Rodrı́guez-Varela and his colleagues compared some 300 genomes from people buried in Scandinavia over the last 2,000 years to the genomes of more than 16,000 modern-day Scandinavians as well as more than 9,000 people whose ancestors hailed from other places across Europe and western Asia. They found that Viking Age Scandinavia was much more genetically diverse than modern Scandinavia.

Rodrı́guez-Varela and his colleagues found threads of ancestry stemming from the eastern Baltic coast, the far southern edge of Europe, and Britain and Ireland running through the genomes of people from the Viking Age and early Medieval Scandinavia.

That the Viking Age was diverse isn’t too surprising; a previous study found similar results, which suggested that ancient Scandinavian peoples swapped DNA pretty freely with the other people they encountered — sometimes with all parties’ consent and sometimes not. The result was that Viking society was far from homogeneous and surprisingly cosmopolitan, especially in large cities.

The Viking era was defined by seaborne travel and trade. But the DNA of people who lived during this age suggests the Vikings weren’t alone in sowing wild oats overseas. People came from abroad to Scandinavia, too, and they did so in numbers large enough to show up in the region’s gene pool.

The twist — What’s more surprising is that a few centuries after the end of the Viking Age, the genetic traces of those interactions had mostly faded out. The people who came to Scandinavia during the heyday of Viking raiding and trading — whether they were merchants, missionaries, or enslaved captives — have all but vanished from the gene pool of modern-day Scandinavia.

“The drop in current levels of external ancestry suggests that the Viking period migrants got less children, or somehow contributed proportionally less to the gene pool than the people who were already in Scandinavia,” paper co-author and Stockholm University geneticist Anders Götherström tells Inverse.

Here’s The Background — Shortly after the fall of the Roman Empire, small kingdoms started popping up in Scandinavia. The newly-risen ruling class needed money, and that need — along with a host of other factors, including climate shifts — fueled what became known as the Viking Age.

Even before the 793 C.E. raids on Lindisfarne Monastery in Ireland marked the start of a new period of expansion, Scandinavian kingdoms had established trade networks reaching all the way to the Middle East and taken mercenary contracts in places as far-flung as Constantinople.

Archaeologists have found Arabic script woven into the fabric of clothing in Viking boat burials, making it clear that cultural exchange happened on a regular basis — and human nature means that sometimes the exchange must have been personal, too. But most of these individual stories of how people met and mingled and interacted don’t make it into the genome several generations later; the signal isn’t strong enough, and eventually, it fades into the background and is lost. Rather, a population’s gene pool reveals major, large-scale trends over a long period of time, not individual relationships.

It’s perhaps no surprise, then, that the populations who influenced the Viking gene pool the most came from across Europe, within the range of trade networks, rather than even farther afield.

It’s also not surprising that traces of ancestry from Baltic and southern European immigrants faded out of circulation in Scandinavia within a few centuries of the Viking Age. These migrants left enough of a mark on Scandinavia’s gene pool to last a few centuries, but not longer than that. British and Irish ancestry still shows up in modern Scandinavian genomes, though, albeit in small amounts.

“This is perhaps not surprising, given the extent of Norse activities in the British Isles starting in the 8th century… and culminating in the 11th century North Sea Empire,” writes Rodriguez-Varela and his colleagues in the paper. Interactions with other people in other places were less intense and didn’t last quite as long.

Why it matters — If you take nothing else from this study, take this: genomes usually reveal only the biggest, broadest strokes of human interactions. Even major events in the past get lost. Nuance gets lost.

DNA tells one piece of the story, and archaeology and written history tell other pieces. The best way to understand the past is a combination of those lines of evidence. For example, Rodrı́guez-Varela and his colleagues found that the increase in eastern Baltic ancestry in Gotland and central Sweden lined up with the timing of treaties and other events. Without the written history, we wouldn’t know what factors pulled people from the Baltic into Sweden. Without genetic history, we wouldn’t know the important results of those treaties and trade relationships on the people.

Testing your genetic ancestry with a home kit is fun, and many people are eager to brag about being descended from Vikings for whatever reason. But studies like this suggest this ancestral picture is more complicated than most people realize.

For one thing, ancient genomes challenge the idea that Vikings were a force acting on the rest of the world without being influenced in return. People migrating to Scandinavia left their mark, which suggests we shouldn’t view the Vikings as actors and everyone in their path as passive. Scandinavia was impacted by those Viking Age interactions as well.

It’s also clear that many people in modern Scandinavia are descended from people who originally came from elsewhere, even if those genetic clues have now been lost. That means that whatever your at-home DNA ancestry kit tells you (and there’s plenty of reason to take those results with a hefty grain of salt), your ancestors’ actual history is probably more complicated — and more diverse — than it looks on paper.