Population genomics of the Viking world

The Viking Age maritime expansion of Scandinavian populations (c. 750 to 1050 CE) was a far-flung transformation in world history. To understand its global influence, we sequenced the genomes of 442 ancient humans (median depth of c. 1X) from across Europe and Greenland. We find the Viking period involved foreign gene flow into Scandinavia from the south and east. We observe genetic structure within Scandinavia, with diversity hotspots to the south and restricted gene flow within Scandinavia. We find evidence for a major Danish influx in England, Swedish influx in the Baltic, and Norwegian influx in Ireland, Iceland, and Greenland. Additionally, we see substantial foreign European ancestry entering Scandinavia during the Viking Age. We show that a Viking expedition included close family members. We find that pigmentation-associated loci have undergone strong population differentiation during the last millennia. We trace positively selected loci with unprecedented detail, including the lactase persistence allele and alleles associated with the immune response. We conclude that the Viking diaspora was characterized by substantial trans-regional engagement: distinct populations influenced the genomic makeup of different regions of Europe, while Scandinavia experienced increased contact with the rest of the continent.