A new study using 297 ancient Scandinavian genomes and the genomic data of 16,638 modern Scandinavians resolves the complex relations between geography, ancestry, and gene flow in Scandinavia, encompᴀssing the Roman, Viking, and later periods. A surprising increase in variation during the Viking period suggests that gene flow into Scandinavia was especially intense during this time.

Model of the ship Kronan. Credit: Alexander Vogel

An international study led by Stockholm and Reykjavik looks at the development of the Scandinavian gene pool over the latest 2000 years. The scientists relied on historic and prehistoric genomes, and material excavated in Scandinavia. These ancient genomes were compared with genomic data from 16,638 contemporary Scandinavians. Because the geographical origins and datings of all these individuals were known, it was possible to resolve the development of the gene pool to a level never before realized.

“With this level of resolution we not only confirm the Viking Age migration. We are also able to trace it to the east Baltic region, the British-Irish Isles, and southern Europe. However, not all parts of Scandinavia received the same amounts of gene flow from these areas. For example, while British-Irish ancestry became widespread in Scandinavia the eastern-Baltic ancestry mainly reached Gotland and central Sweden,” Dr Ricardo Rodríguez Varela at the Centre for Palaeogenetics, who analyzed all the data and extracted some of the ancient DNA used in the study, explains.

The gene pool bounced back after the Viking period
This study also revealed what happened to the gene pool after the Viking period. The scientists were surprised when they discovered that it bounced back in the direction of what it looked like before the Viking period migration.

“Interestingly, the non-local ancestry peaks during the Viking period while being lower before and after,” says Professor Anders Götherström of the Centre for Palaeogenetics, who is a senior scientist in the study. The drop in current levels of external ancestry suggests that the Viking-period migrants got fewer children, or somehow contributed proportionally less to the gene pool than the people who were already in Scandinavia.”

Yet a new discovery was the history of the northern Scandinavian gene pool. There is a genetic component in northern Scandinavia that is rare in central and western Europe, and scientists were able to track this component in northern Scandinavia through the latest 1000 years.

“We suspected that there was a chronology to the northern Scandinavian gene pool, and it did indeed prove that a more recent influx of Uralic ancestry into Scandinavia define much of the northern gene pool. But if it is recent, it is comparatively so. For example, we know that this Uralic ancestry was present in northern Scandinavia as early as during the late Viking period,” Dr Ricardo Rodríguez Varela comments.

Based on well-known Swedish archaeological sites

The research is based on a number of well-known Swedish archaeological sites. For example, there are genomes from the 17th-century warship Kronan, from the Viking and Vendel period boat burials in the lake Mälaren Valley, and from the migration period ring fortress Sandby borg on Öland.

“We were working on a number of smaller studies on different archaeological sites. And at some point it just made sense to combine them into a larger study on the development of the Scandinavian gene pool,” Anders Götherström concludes.

Provided by Stockholm University

More information: Rodríguez-Varela, R, et. al. (2023). The genetic history of Scandinavia from the Roman Iron Age to the present. Cell; 186 (1): 32 DOI: 10.1016/j.cell.2022.11.024