The mapping of DNA from some of the settlers who colonised Iceland more than 1,000 years ago offers an insight into the fate of thousands of slaves – mostly women – who were taken by Norse Vikings from Ireland and Scotland before they put down roots on the North Atlantic island.

Anthropologist Sunna Ebenesersdóttir, of the University of Iceland and the company deCODE Genetics in Reykjavik, analysed the genomes of 25 ancient Icelanders whose skeletal remains were found in burial sites across the island.

Sequencing using samples from teeth revealed the settlers had a roughly even split of Norse (from what are today Norway and Sweden) and Gaelic ancestry. It is the first in-depth investigation of how a new population is formed through a genetic process known as “admixture”.

When the researchers compared the ancient genomes to those of modern people in Iceland and other European countries, they found contemporary Icelanders, on average, draw about 70 per cent of their genes from Norse ancestry.

This suggests that in the 1,100 years between settlement and today, the population underwent a surprisingly quick genetic shift in favour of Norse genes, the researchers report in the journal Science.

Indistinguishable

They confirm that while the ancient settlers, “mainly Norse men and Gaelic women”, are genetically indistinguishable from present-day Irish, Scots and Scandinavians, present-day Icelanders have over the course of 1,000 years, and numerous population bottlenecks, become a distinct new population.

“Repeated famines and epidemics led to a substantial loss of sequence diversity from the Icelandic gene pool, causing it to drift away from its source populations in Scandinavia and the British-Irish Isles,” explained Kári Stefánsson, deCODE chief executive and co-author on the paper.

Another possibility, he suggested, is that ancient Icelanders with more Norse ancestry held a slight edge in reproductive success over those with Gaelic ancestry, many of whom were enslaved when they came to the island.

The Celts were often buried in unmarked graves though, intriguingly, a minority were buried in the traditional Viking way, with their sword and boat.

On the study, he added: “This is a fascinating example of how a population is shaped by its environment, in this case the harsh and marginal conditions of medieval Iceland.

“It is also another demonstration of how our small but well characterised population can continue to make important contributions to understanding the fundamental genetic and evolutionary processes that shape our species.”

Their next step is to expand sample size, and to examine how diseases affected the population.