Population genomics, demography, and circum-Baltic connectivity of Early Medieval southwestern Finland

AI interpretationAI-generated

Ancient DNA reveals 1,000 years of inland continuity but a major coastal shift in medieval Finland.

Researchers sequenced 34 ancient genomes from southwestern Finland (1050–1250 CE) and compared them with modern Finns. Inland early medieval people were genetically very similar to today's inhabitants, showing long-term continuity. In contrast, coastal populations have since gained much more Scandinavian ancestry and lost Baltic ancestry, indicating a large genetic shift after the medieval period. This shift matches historical records of Swedish migration to Finland. The population also grew rapidly, reaching an effective size of about 13,000 by 1250 CE, likely helped by new farming and a favorable climate.

• Inland southwestern Finland shows nearly a millennium of genetic continuity from the Early Medieval period to today.
• Coastal Finland experienced a major genetic shift after the Early Medieval period, with increased Scandinavian and decreased Baltic ancestry.
• The effective population size grew throughout the study period, reaching about 13,000 by 1250 CE.

Sample interpretation

The study analyzed 38 site samples, with 18 Y-chromosome haplogroups resolved. The most common Y lineages were N-Z1927 (3), N-Z1957 (2), and N-Y7300 (2), alongside I-DF29, N-FT12605, I, N-M2126, and I-M253. Mitochondrial DNA was less diverse: J2a1a1a1 appeared 3 times, H27a twice, and H1h1, H2a1-T146C!, H5b2, and J1c2 once each. By culture, 26 samples were Early Medieval Period, 9 Late Iron Age/Early Medieval Finland, 2 Late Iron Age, and 1 outlier (PRK001_Outlier).

For genealogy enthusiasts

For ancestry enthusiasts, this study shows that modern Finnish coastal ancestry is not simply a continuation of the medieval past. It highlights how migration, especially from Sweden, reshaped coastal gene pools, while inland populations remained stable for centuries.