DNA reveals how early Iron Age Scandinavia was settled from southern Europe

There were three key waves of migration in Europe in the first millennium, new genetic analysis of populations indicates

Roman fort at Housesteads, Northumberland, in England. Getty Images

Roman soldiers and slave gladiators living in the UK more than 1,500 years ago descended from early Iron Age Scandinavians, while a person from the same era in southern Europe had 100 per cent Scandinavian roots, scientists have found.

The common link is migration. Using a new detailed method, researchers studied more than 1,500 genomes – the complete set of a person’s DNA – among people who lived in Europe during the first millennium AD, year 1 to 1000. The period includes the Iron Age, the fall of the Roman Empire, and the Viking Age.

Researchers uncovered genetic evidence of widespread population migration during the Viking Age, when people from Scandinavia raided and settled throughout Europe. The experts discovered ancestry from present-day Sweden in some people who lived in Ukraine and Russia, and also patterns flowing back in the other direction.

They also found people living in the UK with ancestry from present-day Denmark, while the remains of a group of men who died violently in Britain showed genetic links to Scandinavia, suggesting they may have been executed for raiding, say researchers.

“We already have reliable statistical tools to compare the genetics between groups of people who are genetically very different, like hunter-gatherers and early farmers, but robust analyses of finer-scale population changes, like the migrations we reveal in this paper, have largely been obscured until now,” said Leo Speidel, first author and former postdoctoral researcher at the Francis Crick Institute and University College London.

“Our new method can be applied to other populations across the world and hopefully reveal more missing pieces of the puzzle,” added Dr Speidel.

The study, published in Nature, discovered three waves of migration during the period – the movement of Germanic people from 1-500 AD into the Roman Empire; expansion into Scandinavia by 800AD; and migration after 800AD from Scandinavia to elsewhere in Europe during the Viking Age.

Big waves

In the first wave, groups migrated south from Northern Germany and Scandinavia during the first millennium. Researchers found their ancestry among people in southern Germany, Italy, Poland, Slovakia, and southern Britain.

Genetic analysis also revealed a second wave of migration northward into Scandinavia at the end of the Iron Age in 300-800 AD, explaining why many Viking Age individuals across southern Scandinavia also carried ancestry from Central Europe.

A separate analysis of teeth of people buried on the island of Oland, Sweden, where they grew up locally, discovered they carried ancestry from Central Europe, suggesting the northward influx of people wasn’t a one-off, but a lasting shift.

Twigstats

“Historical sources indicate that migration played some role in the massive restructuring of the human landscape of western Eurasia in the second half of the first millennium AD which first created the outlines of a politically and culturally recognisable Europe, but the nature, scale and even the trajectories of the movements have always been hotly disputed,” said Peter Heather, professor of medieval history at King’s College London, and co-author of the study.

The method, a mathematical model called Twigstats, examines genetic mutations – identifying people who are more closely related by the number of mutations they share, helping to build family trees, map how old the mutations are and who they are shared by.

Twigstats examines genetic family trees to work out who people have inherited their DNA from, studying more recent mutations to reveal connections between people who lived closer together in time.

Researchers used the method to help track migrations across Europe in detail for the first time – discovering that 25 per cent of the DNA of someone who could have been a Roman soldier or slave gladiator living in York in the 2nd to 4th century came from early Iron Age Scandinavia, around 5th to 1st centuries BC.

“Twigstats opens up the exciting possibility of finally resolving these crucial questions.”