A new study led by the University of Turku offers new understanding of Finland's population history during the Late Iron Age and the Middle Ages. Researchers examined the genomes of people who lived in southwestern Finland and the region of Häme between the 11th and 13th centuries. Their goal was to understand how the population changed over time and how people in Finland were connected to other regions around the Baltic Sea. The findings, published in the journal Genome Biology, highlight a notable difference in the population histories of coastal and inland areas of Finland. During the Early Medieval period (1050–1250 CE), the people living in coastal and inland southwestern Finland were genetically very similar, despite the cultural and economic differences between the regions. However, after this time, the genetic makeup of these groups began to diverge. Inland areas retained a genetic continuity that persists to the present day, while the coastal population experienced a significant shift in genetic composition after the Middle Ages. This change is largely attributed to migration from Sweden, which left a lasting genetic legacy along Finland's coast. Today, people living in coastal areas have a much higher proportion of Scandinavian ancestry compared to those living in the same region around 1,000 years ago. The study also highlights the extent to which Finland was connected to broader networks across the Baltic Sea. Researchers looked at ancient DNA samples from various parts of the Baltic region to identify genetic relatives and track human movement. Individuals from Early Medieval Finland were found to have genetic links with Viking Age Sweden, the island of Gotland, Latvia, and the Lake Ladoga region. The strongest genetic ties were with Gotland, which was a crucial hub for trade and movement in the Baltic Sea. One intriguing discovery involved two individuals who died when the Swedish warship Kronan sank in 1675. These individuals shared DNA segments with people from Early Medieval Finland. Historical records indicate that Finns were recruited to serve on the Kronan, and the genetic evidence supports the idea that some of those on board had Finnish roots. The study suggests that large-scale migration from Sweden to Finland began during the Middle Ages, though people had been moving across the Baltic Sea earlier than 1250 CE. Overall, the research shows that Finland was never isolated from the wider Baltic world, and its people were deeply integrated into the international networks that shaped the region during this period.