New genomic data suggest that the first human settlers on the Scandinavian peninsula followed two distinct migration routes. The study publishing January 9 in the open access journal PLOS Biology led by researchers from Uppsala University with an international team of collaborators, also indicates that the resulting mixed population genetically adapted to the extreme environmental conditions.

There is consistent evidence of a human presence in the Scandinavian peninsula from around 11,700 years ago, and similarities between stone tool artefacts found in Scandinavia and those seen in both Western Europe and Eastern Europe suggest that several groups may have migrated into the area when the ice retreated. The migration routes and genetic makeup of the first Scandinavians have, however, previously been elusive.

By sequencing the genomes of 7 hunter-gatherers excavated across Scandinavia and dated to be 9,500-6,000 years old, the researchers found that migrations into the Scandinavian peninsula most likely followed two routes; one from central Europe and one from the Northeast along the Norwegian Atlantic Coast. The two groups met and mixed in Scandinavia, creating a genetically diverse population with many genetic variants that have not been passed down to modern-day Europeans.

The research team also investigated whether the individuals showed signs of adaptation to the cold and low daylight conditions found in high-latitude environments. They discovered that several genetic variants in the hunter-gatherers were linked to a gene associated with physical performance, which they hypothesise could be part of the physiological adaptation to cold. The hunter-gatherers also had a high frequency of genetic variants linked to reduced skin pigmentation -- a known adaptation to environments with low UV radiation, such as those at high latitude.

"We used cutting-edge genomic approaches to investigate hypotheses about the early colonization of northern Europe after the ice-sheet of the last glaciation retracted. It is really great to see how evidence from different disciplines can be combined to understand these complex past demographic processes," said population geneticist Torsten Günther, one of the lead authors. He adds: "Our findings are important for human genetics, archaeology and anthropology, and it will be interesting to see what similar approaches can tell us about the post glacial population dynamics in other parts of Europe and the rest of the world."