On May 31, 2018, deCODE genetics published new findings about the founding of the Icelandic population, and its subsequent evolution, based on ancient DNA. The study appeared in the online edition of Science.

Iceland was settled around 1100 years ago, at the height of the Viking age. By sequencing the genomes from 25 ancient skulls dating to the first generations of settlement, and comparing them to genomes from the contemporary inhabitants of Iceland, Scandinavia and the British and Irish Isles, the deCODE team was able to demonstrate that most of the settlers were of unmixed Norse or Gaelic ancestry. Some were already admixed on arrival to Iceland, and presumably originated from Viking settlements in the British and Irish Isles. Norse ancestry in Iceland increased from 57% at the time of settlement to 70% today. This change may be explained by less reproductive success of Gaelic settlers, many of whom were taken to Iceland as slaves. Another contributing factor could be later immigration from Denmark.

A striking finding of the study is that as a result of genetic drift, contemporary Icelanders have diverged from their ancestors in Scandinavia and the British and Irish Isles, while the Viking age settlers are effectively indistinguishable from modern representatives of these source populations. Finally, the new study reports the first discovery of an individual with Klinefelter syndrome based on ancient DNA.