Evidence of massive migration to Ireland thousands of years ago has emerged from the sequencing of the first genomes from ancient Irish humans, carried out by geneticists from Trinity College Dublin and archaeologists from Queen's University Belfast.
Sequencing the genome of an early woman farmer, who lived near Belfast 5,200 years ago, showed her majority ancestry originated in the Middle East, where agriculture was invented.
Sequencing the genomes of three men whose bodies dated from the Bronze Age about 4,000 years ago showed one-third of their ancestry came from the Pontic steppe on the shores of the Black Sea.
The woman farmer had black hair, brown eyes and resembled southern Europeans, according to the researchers.
In contrast, the three men, who were from Rathlin Island, had the most common Irish Y chromosome type, blue eyes alleles and the most important variant for the genetic disease haemochromatosis, or excessive iron retention.
The latter mutation is so frequent in people of Irish descent that it is sometimes referred to as a Celtic disease.
This discovery therefore marks the first identification of an important disease variant in prehistory, according to the researchers.
A genome is an organism’s complete set of DNA, including all of its genes.
Each genome contains all of the information needed to build and maintain that organism.
Discovering the sequence of the human genome provides a first step in understanding how the instructions coded in DNA lead to a functioning human being.
The information buried in the genes of ancient bodies is already answering pivotal questions about the origins of Ireland’s people and contemporary cultures, according to the study, published in the international journal Proceedings of the National Academy of Sciences of the USA.
"There was a great wave of genome change that swept into Europe, from above the Black Sea into Bronze Age Europe, and we now know it washed all the way to the shores of its most westerly island," said professor of population genetics in Trinity College Dublin, Dan Bradley, who led the study.
“And this degree of genetic change invites the possibility of other associated changes, perhaps even the introduction of language ancestral to western Celtic tongues.”
Time travel
Ireland is considered to have intriguing genetics. It has the highest rates of variants that code for lactose intolerance, the western European Y chromosome and several important genetic diseases.
However, the origins of this genetic heritage are unknown.
The only way to discover our genetic past is to sequence genomes directly from ancient people, by embarking on a type of genetic time travel, said Prof Bradley.
In archaeology, opinion has been divided on whether the great transitions in the British Isles from a hunter-gatherer lifestyle to one based on agriculture, and the switch from the use of stone to metal, were due to the adoption of new ways by locals or the influences of new people.
Dr Eileen Murphy, a lecturer in osteoarchaeology at Queen's University, said the project has demonstrated how ancient DNA analysis can provide the tools to answer such questions.
The ancient Irish genomes sequenced for this study show “unequivocal” evidence for massive migration to Ireland, she said.
"Genetic affinity is strongest between the Bronze Age genomes and modern Irish, Scottish and Welsh, suggesting establishment of central attributes of the insular Celtic genome 4,000 years ago," said Lara Cassidy, a genetics researcher at Trinity.
