A new ancient DNA study reveals that genetic similarities existed between coastal and inland populations in southwestern Finland during the early Middle Ages, prior to Swedish migration altering the makeup of the coastal inhabitants. Published in Genome Biology, the research offers a clearer picture of how migration, trade, and population growth shaped Finland during the Viking Age and the medieval era.
Genomes Reveal Early Medieval Similarities
Researchers led by the University of Turku analyzed genomes from human remains recovered at 17 archaeological sites in southwestern Finland. Out of 38 sampled individuals, 34 produced data suitable for main analyses. Most dated from the Early Medieval period between 1050 and 1250 CE, while two belonged to the Late Iron Age.
Despite economic and material cultural differences—such as strong Scandinavian connections on the coast and eastern-western influences inland in Häme—the genetic evidence indicates that ancient coastal and inland inhabitants were very similar around a thousand years ago. According to lead author Ronan James O’Sullivan, people were already moving across the Baltic Sea earlier than 1250 CE, but large-scale migration from Sweden to Finland took place later.
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Historical recruitment records from the area are reflected by the fact that two individuals who perished on the Swedish warship Kronan—which went down during the 1675 Battle of Öland—shared remote genetic ties to early medieval people from Finland.
Coastal Transformation and Inland Continuity
The genetic trajectories of these two populations diverged significantly after the early medieval period. Inland southwestern Finland exhibits nearly 1,000 years of population continuity, with modern inhabitants retaining strong genetic links to early medieval residents.
Along the coast, however, modern populations show an approximately 25-percentage-point increase in Scandinavian-derived ancestry compared to ancient coastal inhabitants, alongside reduced Baltic-derived ancestry. Researchers attribute this shift to large-scale immigration from Sweden that intensified mainly after the thirteenth century as southwestern Finland integrated into the Kingdom of Sweden.
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As noted by researchers in Genome Biology, the concentration of Swedish settlers near coastal administrative and ecclesiastical centers—facilitated by established maritime routes—demonstrates how political and economic integration directly reshaped regional demographics over centuries.
Circum-Baltic Connections and Trade Networks
The study also details extensive connections linking Finland with the wider Baltic world long before large-scale Swedish settlement. Archaeological finds like Finnish items at Birka in Sweden, alongside imported glass beads, weapons, jewelry, and Islamic, Anglo-Saxon, and Germanic coins in Finland, point to active trade where furs likely served as a primary export.
DNA segments connected individuals in Finland with Viking-Age populations in Sweden, Gotland, Denmark, Norway, Russia, and medieval Latvia. Gotland showed the highest average normalized DNA sharing with Finland, while a woman buried at Laukskola on the Daugava River between 1031 and 1147 shared DNA with two southwestern Finland individuals at a level consistent with distant kinship.
Demographic Growth and Farming
Genetic data tracked an increase in effective population size from roughly 2,500 at the beginning of the Late Iron Age to approximately 13,000 by the end of the Early Medieval period, though researchers note the earlier estimate carries more uncertainty due to fewer sampled individuals. This growth coincided with new plough technologies that eased cultivation of heavy clay soils in southwestern Finland.
Frequently Asked Questions
What did the DNA study discover about coastal and inland Finland?
Researchers found that coastal and inland inhabitants were genetically very similar during the early Middle Ages, but subsequent migration from Sweden after 1250 CE significantly increased Scandinavian ancestry along the coast while inland populations maintained nearly 1,000 years of genetic continuity.
Where was the study published?
The research was published in the journal Genome Biology under the title “Population genomics, demography, and circum-Baltic connectivity of Early Medieval southwestern Finland.”
How far back do Finland’s Baltic trade connections stretch?
Genetic and archaeological evidence demonstrates that Finland was connected to vibrant international networks across the Baltic Sea during the Viking Age, showing shared DNA segments and trade items with Sweden, Gotland, Denmark, Norway, Russia, and Latvia.
How might future ancient DNA studies alter our understanding of medieval demographic shifts across northern Europe?
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