Coastal and inland residents of southwestern Finland were genetically very similar between 1050 and 1250 CE, but their populations followed different paths afterward. A University of Turku release published on 15 September 2026 reports that genetic continuity persisted inland, while the modern coastal population carries considerably more Scandinavian ancestry than people from the same region about a thousand years ago. The researchers attribute the later coastal shift to migration from Sweden after the Early Medieval period.
This is a finding about population patterns in sampled DNA—not a dividing line between individual Finns, nor a claim about every coast and inland region in Finland.
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What changed between the medieval coast and inland?
The University of Turku’s account of the ancient-DNA study describes a contrast across time. In southwestern Finland, coastal and inland residents were genetically similar in the period 1050–1250 CE, despite cultural and economic differences. Inland genetic patterns then show continuity to the present, while coastal patterns changed after the Middle Ages.
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallThe release says people living in the coastal region today have considerably more Scandinavian ancestry than people from that same region around a thousand years ago. It attributes that broader change to migration from Sweden after the Early Medieval period. The source does not provide a percentage estimate for the increase, so the finding is best described comparatively rather than as a quantified share.
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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”.
Does this mean Finland was isolated before Swedish migration?
No. The same study reports earlier connections across the Baltic. 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. The distinction is between earlier contacts and the later, broader demographic impact attributed to migration from Sweden—not between isolation and first contact.
O’Sullivan put the wider context this way: “Finland was never isolated from the wider Baltic world,”
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The new coast–inland comparison concerns southwestern Finland, including research on Häme. It should not be generalized into a coast-versus-interior rule for the whole country. “Genetically divided” refers to differences in population-level patterns across sampled groups and periods; it does not mean that every coastal person shares one ancestry or that individuals can be sorted into two discrete genetic categories.
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FinnGen’s overview describes Finnish regional genetic differences as slight overall and largely associated with historical settlement patterns and small founding populations. It also identifies founder effects, bottlenecks, geographic and cultural isolation, and later population expansion as forces shaping Finland’s population history. That national overview provides context, but it is not a substitute for the specific southwestern ancient-DNA comparison.
How is this different from Finland’s east–west genetic structure?
A separate 2017 study, Fine-Scale Genetic Structure in Finland, describes a broad east–west division in modern Finnish genetic patterns. It reports that this division corresponds strikingly with settlement history and the approximate 1323 boundary of the Treaty of Nöteborg. That nationwide pattern is not the same result as the newer comparison of ancient and modern populations along the southwestern coast and inland.
| Finding | Geography and time | Evidence and interpretation |
|---|---|---|
| Medieval-to-modern coast–inland change | Southwestern Finland, including Häme; similarity reported for 1050–1250 CE, followed by different later trajectories | Ancient genomes compared with modern evidence; the release attributes the later coastal shift to migration from Sweden after the Early Medieval period. |
| East–west genetic structure | National pattern, reflecting historical settlement; study focuses on structure before internal migrations from around the 1950s onward | Modern population-genetic clustering; the 2017 study reports correspondence with settlement history and the approximate 1323 treaty boundary, not proof that the treaty caused the division. |
The 2017 authors explicitly caution that the Treaty of Nöteborg boundary was administrative and likely did not restrict ordinary movement. Its alignment with genetic structure is better understood alongside settlement history and shared historical geography, rather than as evidence that a border physically divided populations. The study also describes later settlement in eastern and northern regions, including migration mainly from Southern Savonia beginning in the 16th century.
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The datasets behind the national result have distinct scopes. The 2017 paper reports a geographically selected FINRISK reference dataset of 2,376 people; some analyses use a 1,042-person subset. The University of Helsinki’s visualization describes 1,042 individuals whose parents were both born within 80 km of one another, excludes close-relative pairs, and uses 230,000 genomic positions. These figures describe specific modern datasets and analyses, not the ancient-DNA study.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What can ancient maternal DNA tell us?
A University of Helsinki summary of a 2019 study reports mitochondrial DNA from archaeological bone samples of more than 100 people who lived between the 4th and 19th centuries CE. Mitochondrial DNA follows maternal lines, so it illuminates only one line of ancestry for each person; it is not a genome-wide account of entire populations.
The summary describes different patterns among archaeological sites:
- 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 maternal-lineage observations demonstrate the varied ancestry represented in the region’s past. They do not establish the cause or scale of the coastal change reported in the later genome-wide comparison.
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Sources and evidence
- University of Turku, “Ancient DNA traces medieval migration from Sweden to Finland,” 15 September 2026.
- G3: Genes, Genomes, Genetics, “Fine-Scale Genetic Structure in Finland,” 2017.
- University of Helsinki HiLIFE, “Population Genetics of Finns,” 2017.
- FinnGen, “Population genetic history”.
- University of Helsinki, “Early DNA lineages from Finland shed light on the diverse origins of the contemporary population,” summarizing 2019 research.
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