Immigrants to Sweden from the east at the time, on the other hand, do not seem to have had as many children, a new study shows. People often speak of the Vikings as a traveling people, with contacts far out in the world. Now a new Swedish-Icelandic study of ancient DNA shows that the period between the year 750 and 1050 also meant a peak in immigration of people to Denmark, Norway and Sweden.
The study, based on 297 ancient Scandinavian genomes analyzed together with the genomic data of 16,638 present day Scandinavians, resolves the complex relations between geography, ancestry, and gene flow in Scandinavia – encompassing the Roman Age, the Viking Age and later periods. A surprising increase of variation during the Viking period indicates that gene flow into Scandinavia was especially intense during this period.
Another new discovery in this study was what happened to the gene pool after the Viking period. The scientists were surprised to find that it bounced back in the direction of what it looked like before the Viking period migration. Professor Anders Götherström at the Centre for Palaeogenetics, who is a senior scientist on the study, is intrigued: “Interestingly, the non-local ancestry peaks during the Viking period while being lower before and after. 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.”

Northern Scandinavian gene pool
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 the scientists were able to track this component in northern Scandinavia through the latest 1000 years.
The study 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.
Anders Götherström concludes: “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."
The study, published in Cell in January, is an international effort with several collaborators led by Dr. Ricardo Rodríguez Varela and Professor Anders Götherstörm at Stockholm University, and Professor Agnar Helgason and Kristjáan Moore at deCODE in Reykavijk.


The Centre for Palaeogenetics (CPG) is a joint venture between Stockholm University and the Swedish Museum of Natural History - The article “The genetic history of Scandinavia from the Roman Iron Age to the present” was published in the journal Cell, which publishes findings of unusual significance in any area of experimental biology.