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Ancient DNA suggests that people in coastal and inland southwestern Finland were genetically similar between 1050 and 1250 CE, but their populations followed different paths afterward. A University of Turku release dated 15 September 2026 attributes the later increase in Scandinavian ancestry along the coast to migration from Sweden after the Early Medieval period. The finding describes population-level patterns in sampled DNA—not a genetic boundary separating individuals—and it applies to this southwestern comparison, not every Finnish coast and interior.
What the 1,000-year comparison found
The University of Turku’s account of the study compares ancient genomes from southwestern Finland, including the coast and Häme, with modern evidence. It reports that coastal and inland residents were genetically very similar during 1050–1250 CE. The inland population shows continuity to the present, while the coastal population changed after the Middle Ages. Modern people in the coastal region have considerably more Scandinavian ancestry than people from the same area around a thousand years ago. University of Turku, 15 September 2026.
“Genetically divided” is therefore shorthand for a difference in population-level ancestry patterns across time. It does not mean that everyone on one side shares the same ancestry or differs categorically from everyone on the other. The release does not give a percentage estimate for the increase in Scandinavian ancestry, so the size of the change should not be expressed as a specific number.
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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteWhy the coast changed—and why Finland was not isolated
The Turku release interprets the later coastal shift as the result of migration from Sweden after the Early Medieval period. Lead author Ronan James O’Sullivan, a postdoctoral researcher, said: “Our findings suggest that migration from Sweden began to have a broader impact on Finland’s population relatively late, during the Middle Ages”. The evidence, as summarized in the release, points to a later population impact; it does not imply that contact across the Baltic began then.
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Early Medieval individuals from Finland had genetic links to Viking Age Sweden, Gotland, Latvia, and the Lake Ladoga region, with the strongest reported links to Gotland. O’Sullivan summarized the broader context: “Finland was never isolated from the wider Baltic world,”. Earlier connections and later migration are compatible: the study’s interpretation is that movement existed before the coastal population experienced a broader impact from migration from Sweden. University of Turku’s account of the findings.
How this differs from Finland’s east–west genetic structure
A separate, nationwide pattern is described in the 2017 study Fine-Scale Genetic Structure in Finland. It reports a main east–west division in Finland and a notable correspondence between that structure, settlement history, and the approximate 1323 boundary of the Treaty of Nöteborg. This is not the same result as the newer comparison between coastal and inland southwestern Finland.
The 2017 authors caution that the treaty boundary was administrative and likely did not restrict ordinary movement. Its alignment with genetic structure does not establish that the treaty physically caused the division. A more careful interpretation is that the correspondence may reflect shared historical geography and settlement processes. The study also describes later settlement in eastern and northern regions, including migration mainly from Southern Savonia beginning in the 16th century. “Fine-Scale Genetic Structure in Finland,” G3: Genes, Genomes, Genetics (2017).
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| Finding | Geographic scope and time | Evidence and interpretation |
|---|---|---|
| Coastal–inland change | Southwestern Finland, including comparison with Häme; ancient period includes 1050–1250 CE, followed by later change | Ancient genomes compared with modern evidence; the Turku release attributes the broader later coastal Scandinavian ancestry signal to migration from Sweden after the Early Medieval period. |
| East–west structure | Nationwide pattern; study focuses on structure before internal migrations from around the 1950s onward | Modern genetic clustering and historical correspondence with settlement and the approximate 1323 boundary; correspondence does not prove the treaty caused the structure. |
The datasets behind the national study also have distinct scopes. Its geographically selected FINRISK reference dataset included 2,376 people; some analyses used a 1,042-person subset. The University of Helsinki visualization describes 1,042 individuals whose parents were both born within 80 km of one another, excludes close-relative pairs, and reports using 230,000 genetic positions. Those figures describe particular datasets and analyses, not the number of people in Finland or the ancient-DNA sample. Study methods; University of Helsinki, “Population Genetics of Finns”.
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What ancient maternal lineages add—and what they cannot show
A University of Helsinki summary of a 2019 study reports mitochondrial DNA from archaeological bones of more than 100 people who lived between the 4th and 19th centuries CE. Mitochondrial DNA traces maternal lines, so these results describe one part of ancestry rather than a genome-wide picture of whole populations.
- At Luistari in Eura and Kirkkailanmäki in Hollola, lineages associated with Stone Age hunter-gatherers were common.
- At sites in eastern Finland and Karelia, farmer-associated lineages were common.
- Many individuals at Levänluhta carried lineages associated with modern Sámi.
These site-specific observations help illustrate the varied population history of the region. They do not establish the cause or scale of the later coastal shift found through genome-wide comparisons. University of Helsinki summary of the 2019 study.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What Finland’s broader population history contributes
FinnGen describes Finland’s population history as shaped by founder effects, bottlenecks, geographic and cultural isolation, and later expansion. It characterizes regional genetic differences as slight overall and largely associated with historical settlement patterns and small founding populations. This national overview provides context, but it does not replace the more geographically specific ancient-DNA finding about southwestern coastal change. FinnGen, “Population genetic history”.
Quick Recap
How to read the findings without overstating them
- Keep the map narrow: the newer result concerns coastal and inland southwestern Finland, with the study also examining Häme; it does not establish the same pattern for every Finnish region.
- Keep the timelines distinct: the newer account compares ancient and modern evidence to describe later coastal change; the 2017 study addresses nationwide fine-scale structure and settlement history.
- Keep the evidence types separate: genome-wide ancestry comparisons, modern clustering, and mitochondrial maternal lineages answer different questions.
- Do not convert association into proof: the 1323 boundary’s correspondence with an east–west genetic pattern is not evidence that the treaty itself blocked movement or caused the pattern.
- Do not invent a magnitude: the Turku release describes considerably more Scandinavian ancestry in the modern coastal population but provides no percentage estimate.
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