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

Modern people like to think a lot about oneself — take globalization, for example. Modern humans would be forgiven for thinking that with the ease of travel and the historical migration of people around the world, most populations have a more diverse genetic record than they did in their supposedly more isolated past. But a new study tracing Viking DNA to modern Scandinavia suggests otherwise.

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

Other times, however, the genetic record of ancient interactions fades over time. That seems to be what happened in the aftermath of the Viking Age in Scandinavia, which today includes Denmark, Norway and Sweden, according to a recent study. Paleogeneticist Ricardo Rodrı́guez-Varelal and his colleagues at Stockholm University and the Center for Paleogenetics studied ancient DNA collected from people buried at sites across Scandinavia dating back 2,000 years. The researchers traced how the Scandinavian genome changed over time – and how immigrants to Northern Europe affected the gene pool.

The results were published on Thursday in the journal Cell.

What is new – Rodrı́guez-Varela and his colleagues compared about 300 genomes from people buried in Scandinavia over the past 2,000 years with the genomes of more than 16,000 modern Scandinavians as well as more than 9,000 people whose ancestors came from elsewhere in Europe and West Asia. They found that Viking Age Scandinavia was much more genetically diverse than modern Scandinavia.

This person, who died in the wreck of the Swedish warship Kronan in 1676, unknowingly made a posthumous contribution to the study. LARS EINARSSON

Rodrı́guez-Varela and his colleagues found strands of ancestry originating from the eastern Baltic coast, the southern edge of Europe and Great Britain and Ireland running through the genomes of people from the Viking Age and early medieval Scandinavia.

That the Viking Age was diverse is not so surprising; an earlier study found similar results, suggesting that ancient Scandinavian people exchanged DNA quite freely with the other people they encountered – sometimes with the consent of all parties and sometimes not. The result was that Viking society was far from homogeneous and surprisingly cosmopolitan, especially in large cities.

The Viking Age was defined by seaborne travel and trade. But the DNA of people who lived in this age suggests that the Vikings were not alone in sowing wild oats abroad. People came from abroad to Scandinavia too, and they did so in numbers large enough to appear in the region’s gene pool.

The twist – What is more surprising is that a few centuries after the end of the Viking Age, the genetic traces of these interactions had largely faded. The people who came to Scandinavia during the heyday of Viking raids and trade – whether they were merchants, missionaries or captive slaves – have all but disappeared from the gene pool in today’s Scandinavia.

– The drop in current levels of external ancestry suggests that the migrants from the Viking Age had fewer children, or in some way contributed proportionally less to the gene pool than the people who were already in Scandinavia, says co-author and geneticist at Stockholm University Anders Götherström. Reverse.

Here’s the background – Shortly after the fall of the Roman Empire, small kingdoms began to appear in Scandinavia. The emerging ruling class needed money, and that need—along with a host of other factors, including climate change—fueled what became known as the Viking Age.

Ancient DNA samples had an eventful journey from muddy archaeological sites to pristine genetics laboratories.David Díaz del Molino

Even before the 793 CE raids on Lindisfarne Abbey in Ireland marked the start of a new period of expansion, Scandinavian kingdoms had established trade networks that reached as far as the Middle East, taking mercenary contracts in places as far away as Constantinople.

Archaeologists have found Arabic script woven into the fabric of Viking boat burials, making it clear that cultural exchange occurred on a regular basis – and human nature means that sometimes the exchange must have been personal as well. 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 is not strong enough and eventually fades into the background and is lost. Rather, a population’s gene pool reveals large, large-scale trends over a long period of time, not individual conditions.

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

Nor is it surprising that traces of ancestry from Baltic and southern European immigrants faded out of circulation in Scandinavia within a few centuries after the Viking Age. These migrants left enough traces in Scandinavia’s gene pool to last a few centuries, but not longer than that. British and Irish ancestry still appears in modern Scandinavian genomes, albeit in small amounts.

“This is perhaps not surprising, given the extent of Norse activities in the British Isles that began in the 8th century … and culminated in the 11th century North Sea Empire,” Rodriguez-Varela and his colleagues write in the paper. Interactions with other people elsewhere were less intense and did not last quite as long.

Why it is important – If you take nothing else from this study, take this: genomes typically reveal only the largest, broadest kinds of human interaction. Even great events of the past are lost. Nuance disappears.

DNA tells one part of the story, and archeology and written history tell other parts. The best way to understand the past is a combination of these pieces of evidence. For example, Rodrı́guez-Varela and his colleagues found that the increase in East Baltic ancestry in Gotland and Central Sweden coincided with the timing of treaties and other events. Without the written history, we would not know what factors drew people from the Baltic Sea into Sweden. Without genetic history, we would not know the important results of these treaties and trade relations on the people.

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

First, ancient genomes challenge the idea that Vikings were a force that acted on the rest of the world without being affected in return. People who migrated to Scandinavia left their mark, which suggests that we should not see the Vikings as actors and everyone in their path as passive. Scandinavia was also influenced by these interactions from the Viking Age.

It is also clear that many people in modern Scandinavia are descended from people who originally came from elsewhere, although these genetic traces have now been lost. That means that no matter what your at-home DNA ancestry kit tells you (and there’s plenty of reason to take these results with a big grain of salt), the actual history of your ancestors is probably more complicated—and more diverse—than it seems the paper.

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