Researchers sequencing the genomes from prehistoric Irish individuals for the first time – a female farmer and three men who lived several thousand years ago – reveal genetic changes that parallel the onset of the Neolithic and Bronze Age transitions in Ireland. The findings are published in Proceedings of the National Academy of Sciences this week.
The Neolithic transition, marked by the advent of farming, was thought to have arrived in Ireland around 3750 BCE. This was followed by the Bronze Age and the introduction of metalworking around 2300 BCE. For decades, researchers have debated over whether these two major cultural shifts were triggered by waves of immigrants from the Near East or the adoption of agriculture by local people who had been on the British Isles during the earlier Mesolithic period.
To investigate, Trinity College Dublin’s Daniel Bradley and colleagues sequenced the whole genomes of prehistoric Irish people using ancient DNA extracted from their remains: a Neolithic female farmer from a tomb in Ballynahatty in what is now Northern Ireland dating back between 3343 and 3020 BCE, and three Early Bronze Age men who lived on Rathlin Island between 2026 and 1534 BCE. The team found unequivocal evidence for massive migration in these ancient Irish genomes. "Our results show that migration was substantial enough to change the genetic character of the population," Bradley tells IFLScience. "Cultural transfer by small scale migration, or even elite individuals, would not be enough to do this."
Despite showing traces of hunter-gatherer ancestry, bones of the Neolithic female suggest she descended from a large group of early farmers who came to the island from the Near East. And based on her similarities with Neolithic samples from Spain as well as modern populations living in the southern Mediterranean, farming may have taken a southern coastal route to reach Ireland – rather than a central European one.
The bones of the three Early Bronze Age men reveal genetic affinities with modern Irish, Scottish, and Welsh people, as well as genetic traces of herders from the Pontic Steppe in Eastern Europe. "There was a great wave of genome change that swept into Europe from above the Black Sea into Bronze Age Europe," Bradley says in a statement, "and we now know it washed all the way to the shores of its most westerly island."
Furthermore, gene variants found in high frequencies in Ireland today – including those that code for blue eyes, persistence of the enzyme lactase (for breaking down milk sugars), and a potentially fatal iron-retention disorder called hemochromatosis (or Celtic disease) – were detected in the bones of the three men. That means these genotypes we see today can be traced back to the Irish Bronze Age.