Archaeogenetics reveals fine-scale genetic continuity and patterns of kinship and health in medieval Finland.

We investigated ancestry, kinship, and health in individuals from three cemeteries in Finland: Tampere Vilusenharju and Pälkäne Ristiänmäki (11th-12th centuries) and Rauniokirkko (13th-19th century). The oldest burials provide insights into Finland's medieval population, otherwise poorly known due to poor bone preservation. Using ancient genomic data, contemporary Finnish Biobank data, and identity-by-descent (IBD) analyses, we identified strong regional continuity between the medieval and modern Finnish populations and evidence for mobility within Finland and between Finland and Scandinavia. Kinship analysis identified a sibling relationship between individuals buried 30 km apart and indicated a shared genetic background for individuals from the three cemeteries. However, individuals buried in physical proximity at Rauniokirkko were not closely related, suggesting that social ties, not family relations, shaped burial practices. The pattern may reflect emerging Christian mortuary norms and community-based burial organization. Pathogen screening revealed potential Yersinia and Treponema infections, shedding light on disease burden in medieval Finland.