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, encompassing 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.

Underwater excavations of the ship Kronan. Credit: Lars Einarsson.

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. But 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 analysed 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 on the study. 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.”