Scientists have sequenced the first ancient human genomes from Ireland - shedding light on the genesis of Celtic populations.
A genome is the instruction booklet for building and maintaining a human - comprising three billion DNA letters.
The work shows that early Irish farmers were similar to southern Europeans.
Genetic patterns then changed dramatically in the Bronze Age - as newcomers from the eastern periphery of Europe settled in the Atlantic region.
Details of the work, by geneticists from Trinity College Dublin and archaeologists from Queen's University Belfast are published in the journal PNAS.
Team members sequenced the genomes of a 5,200-year-old female farmer from the Neolithic period and three 4,000-year-old males from the Bronze Age.
Opinion has been divided on whether the great transitions in the British Isles, from a hunting lifestyle to one based on agriculture and later from stone to metal use, were due to local adoption of new ways by indigenous people or attributable to large-scale population movements.
The ancient Irish genomes show unequivocal evidence for mass migration in both cases.
Wave of change
DNA analysis of the Neolithic woman from Ballynahatty, near Belfast, reveals that she was most similar to modern people from Spain and Sardinia. But her ancestors ultimately came to Europe from the Middle East, where agriculture was invented.
The males from Rathlin Island, who lived not long after metallurgy was introduced, showed a different pattern to the Neolithic woman. A third of their ancestry came from ancient sources in the Pontic Steppe - a region now spread across Russia and Ukraine.
"There was a great wave of genome change that swept into [Bronze Age] Europe from above the Black Sea... we now know it washed all the way to the shores of its most westerly island," said geneticist Dan Bradley, from Trinity College Dublin, who led the study.
