In a recent study published in Cell, researchers investigated the history of Scandinavia for the period from the Roman period (between 1.0 CE and 400.0 CE) to the present, spanning over 2,000 years.
Novel hierarchies emerged in Scandinavia during the period of migrations of individuals (400 CE to 550 CE), with social, economic, and religious power accumulated among elite individuals who profited from networking with Romans. Long-distance mercenary and trading activities improved their status and economic profiles. However, the effects of the migration of Anatolian Neolithic farmers, European Mesolithic hunter-gatherers, and early Bronze Age groups from the Steppe into Scandinavia after the Bronze Age on the genetic pool of Scandinavia have not been well-characterized.
About the study
In the present study, researchers studied the genetic history of Scandinavia over 2,000 years between the Roman Age and the current times.
Whole-genome sequencing (WGS) data of 48 and 249 novel and ancient genomes, respectively, and genotypes of 16,638 modern Scandinavians, were analyzed. Assessment sites included burial sites in chambers and boats, sites such as the Kronan Swedish warship (12 persons) that sank near an island off the southeastern Swedish coast in 1676 CE, and the Sandby borg ringfort.
Individuals were categorized as belonging to five periods of time, which were: the pre-Viking period between 1.0 CE and 749.0 CE, the Viking period (between 750.0 CE and 949.0 CE), the Late Viking period (between 950.0 CE and 1099.0 CE), the Medieval period (between 1100.0 CE and 1349.0 CE), and the period after the Medieval period, between 1350.0 CE and 1850.0 CE.
The gene pools of Scandinavians were separated chronologically and geographically to infer the type and extent of events shaping it for the study period. WGS data of 64 and 13 new and previously documented individuals were generated, from which the team excluded ten individuals with autosomal coverage below 0.1 and six individuals with lesser coverage of genetically-associated individuals with the kinship of third-degree. The team estimated deoxyribonucleic acid (DNA) contamination for mtDNA (mitochondrial DNA) and the X chromosome.
PCA (principal component analyses) were performed based on genotypes for 168,599 single-nucleotide polymorphisms (SNPs) among 9,052 modern persons of 67 populations of west Eurasia. To identify genetic flow from Europe into different Scandinavian groups, three populations of modern individuals were selected as proxies for different European regions, including British-Irish individuals for western Europe, Sardinians for southern Europe, and Lithuanians for eastern (Baltic) Europe.
Further, ancient Norwegian and Swedish individuals were split sub-region-wise as the northern, central, and southern, with the island of Gotland as a distinct region. The team also investigated probable gender bias in the genetic flow into Scandinavian regions. The geographical pattern of Uralic-related ancestry among modern Scandinavian individuals was explored by calculating an f4-statistic [f4(X, Mbuti, Finnish, and Danish]. The Finns and Danes represented the northern and southern ends of the cline, respectively, and X represented 19 and 21 counties in Norway and Sweden, respectively, and Finns also represented a Uralic-origin population.
A considerable increase in gene flow from multiple sources into Scandinavia was observed in the Viking period (especially in south Sweden). There was a probable female bias in inserting eastern Baltic and British-Irish origins among Scandinavians. Genetic descent from the British-Irish Isles in the study period showed long-term effects on the Scandinavian gene pool, such that modern Scandinavians showed more British-Irish descent compared to the Pre-Viking period individuals from similar regions.
The findings were concordant with the extent of Norse actions in the British-Irish islands between the eighth century and the 11th century Empire of the North Sea, including the kingdoms of Norway, England, and Denmark. British-Irish individuals who migrated to Scandinavia in the period varied from slaves who were forcibly migrated to Christian monks and missionaries who migrated voluntarily. A definitive example of British-Irish genetic flow in the late Viking period was the case of sal002, a female of British-Irish descent with high social status, who was buried in a boat in central Sweden.
The findings indicated minimal genetic flow from the British-Irish Isles into Scandinavians before the Viking period; however, the case of VK213, a Danish female of British-Irish descent, buried with no objects during the fifth century, was an exception. More individuals of eastern Baltic descent in the Viking period were identified in central Sweden and Gotland. However, a noteworthy decline of eastern Baltic origin was observed among modern Scandinavians.
The observed north-south clinal pattern of genomic variation among Scandinavians during present times was majorly due to the northwardly increasing Uralic origin present in the Viking period and perhaps even before. The Kronan warship crew members clustering with current-time Finnish exemplified the types of migratory forces for continued Uralic origin among Scandinavians.
The massive changeover within a short time could be due to the intervening genetic flow from different areas with a lesser such origin and previous limitations on reproduction based on social hierarchies stratified by origin relative to the Gaelic and Norse origins during the initial settlement generations in Iceland.
Another explanation could be that individuals of a specific origin could have been over-represented in the records concerning those who were alive in that period in that region, e.g., due to origin-associated differences in funeral customs. However, based on the evidence obtained, it seems difficult to determine the explanation that would most precisely justify region-wise reductions among individuals of eastern Baltic or British-Irish descent.
Overall, the study findings highlighted the impact of migration on the Scandinavian gene pool across 2000 years for the period between the Roman Age and the present. The long-term Scandinavian history appears to be characterized by genomic flow from differently-originated populations, with a profound impact of the Uralic origin in the north-south cline.