2,000 years of genetic history in Scandinavia elucidates Viking age to modern day
A new study reported in the journal Cell on January 5 captures a genetic history across Scandinavia over 2,000 years, from the Iron Age to the present day. This look back at Scandinavian history is based on an analysis of 48 new and 249 published ancient human genomes representing multiple iconic archaeological sites together with genetic data from more than 16,500 people living in Scandinavia today.
Among other intriguing findings, the new study led by Stockholm University and deCODE genetics (Reykjavik) offers insight into migration patterns and gene flow during the Viking age (750–1050 CE). It also shows that ancestries that were introduced into the area during the Viking period later declined for reasons that aren’t clear.
“Although still evident in modern Scandinavians, levels of non-local ancestry in some regions are lower than those observed in ancient individuals from the Viking to Medieval periods,” said Ricardo Rodríguez-Varela of Stockholm University. “This suggests that ancient individuals with non-Scandinavian ancestry contributed proportionately less to the current gene pool in Scandinavia than expected based on the patterns observed in the archaeological record.”
“Different processes brought people from different areas to Scandinavia [at different times],” added Anders Götherström, Stockholm University.
The researchers hadn’t originally planned to piece together Scandinavian history over time and space. Rather, they were working on three separate studies focused on different archaeological sites.
“When we were analyzing the genetic affinities of the individuals from different archaeological sites such as the Vendel period boat burials, Viking period chamber burials, and well-known archaeological sites like the Migration period Sandby borg ringfort, known for the massacre that occurred there [in] 500 CE, and individuals from the 17th century royal Swedish warship Kronan, we start to see differences in the levels and origin of non-local ancestry across the different regions and periods of Scandinavia,” Rodríguez-Varela explained.
“Initially, we were working with three different studies,” Götherström said. “One on Sandby borg, one on the boat burials, and one on the man-of-war Kronan. At some point it made more sense to unite them to one study on the Scandinavian demography during the latest 2,000 years.”
The goal was to document how past migrations have affected the Scandinavian gene pool across time and space to better understand the current Scandinavian genetic structure. As reported in the new study, the researchers found regional variation in the timing and magnitude of gene flow from three sources: the eastern Baltic, the British Irish Isles, and southern Europe.
2,000 years of genetic history in Scandinavia elucidates Viking age to modern day.
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British Irish ancestry was widespread in Scandinavia from the Viking period, whereas eastern Baltic ancestry is more localized to Gotland and central Sweden. In some regions, a drop in current levels of external ancestry suggests that ancient immigrants contributed proportionately less to the modern Scandinavian gene pool than indicated by the ancestry of genomes from the Viking and Medieval periods.
Finally, the data show that a north-south genetic cline that characterizes modern Scandinavians is mainly due to differential levels of Uralic ancestry. It also shows that this cline existed in the Viking Age and possibly even earlier.
Götherström suggests that what the data reveal about the nature of the Viking period is perhaps most intriguing. The migration from the west impacted all of Scandinavia, and the migration from the east was sex biased, with movement primarily of female people into the region. As the researchers write, the findings overall “indicate a major increase [in gene flow] during the Viking period and a potential bias toward females in the introduction of eastern Baltic and, to a lesser extent, British-Irish ancestries.
“Gene flow from the British-Irish Isles during this period seems to have had a lasting impact on the gene pool in most parts of Scandinavia,” they continued. “This is perhaps not surprising given the extent of Norse activities in the British-Irish Isles, starting in the 8th century with recurrent raids and culminating in the 11th century North Sea Empire, the personal union that united the kingdoms of Denmark, Norway, and England. The circumstances and fate of people of British-Irish ancestry who arrived in Scandinavia at this time are likely to have been variable, ranging from the forced migration of slaves to the voluntary immigration of more high-ranking individuals such as Christian missionaries and monks.”
Overall, the findings show that the Viking period in Scandinavia was a very dynamic time, they say, with people moving around and doing many different things. In future work, they hope to add additional genetic data in hopes of learning more about how the ancestries that arrived during the Viking period were later diluted. They’d also like to pinpoint when the north-south cline was shaped based on study of larger ancient datasets from the north.
“We need more pre-Viking individuals form north Scandinavia to investigate when the Uralic ancestry enter in this region,” Rodríguez-Varela said. “Also, individuals from 1000 BCE to 0 are very scarce, [and] retrieving DNA from Scandinavian individuals with these chronologies will be important to understand the transition from the Bronze Age to the Iron Age in this part of the world. Finally, more individuals from the Medieval period until the present will help us to understand when and why we observe a reduction in the levels of non-local ancestry in some current regions of Scandinavia.”
“There is so much fascinating information about our prehistory to be explored in ancient genomes,” Götherström said.
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This research was supported by the Swedish Research Council project ID 2019-00849_VR and ATLAS (Riksbankens Jubileumsfond). Part of the modern dataset was supported by a research grant from Science Foundation Ireland (SFI), grant number 16/RC/3948, and co-funded under the European Regional Development Fund and by FutureNeuro industry partners.
Bibliographic information:
Daskalaki et al.: “The genetic history of Scandinavia from the Roman Iron Age to the present”, Cell, DOI: https://www.cell.com/cell/fulltext/S0092-8674(22)01468-4
Press release from Cell Press.
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DNA from archaeological remains show exceptional immigration to Scandinavia during the Viking era
A new study based on 297 ancient Scandinavian genomes analysed together with the genomic data of 16,638 present day Scandinavians resolve 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.
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:
“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.”
The gene pool bounced back after the Viking 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.”
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 the scientists were able to track this component in northern Scandinavia through the latest 1000 years.
Dr Ricardo Rodríguez Varela comments, “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”.
Based on well-known Swedish archaeological sites
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 conclude: “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 today in Cell, is an international effort with several collaborators, but it was 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” is published in Cell.
This research was supported by The Swedish Research Council Project ID 2019-00849_VR and ATLAS (Riksbankens Jubileumsfond).
Press release from Stockholm University on the study about the genetic history of Scandinavia, elucidating from Viking age to modern day.
