Genome sequencing has revealed new clues to Irish origins.
Image credit: Daniel Bradley, Trinity College
The genetics of Ireland fascinate many. Ireland lies at the edge of several European genetic gradients for variants that code for lactose tolerance, the Western European Y chromosome type and several important genetic diseases, including one of excessive iron retention called hemochromatosis. However, where this heritage comes from has remained a mystery.
The oldest Gaelic literature describes the origins of the Irish people as a series of ancient invasions; Ireland's archaeological record also reflects several major cultural shifts.
In Europe, the advent of agriculture and later of metallurgy constituted the two greatest shifts in prehistory. These innovations brought huge cultural and also, in places, genetic changes.
The current study supports similar transitions in Ireland, accompanied by large-scale genetic shifts.
Two major shifts in prehistoric Ireland
The first change came with the introduction of agriculture, bringing animal husbandry, cereal crops, ceramics and timber houses. This occurred around 3750 BC, or some 5,000 years after it first appeared in the Near East.
The second transition started around 2300 BC, with the appearance of copper mines, quickly followed by Bronze tool-making, weaponry and gold-working, and the evolution of distinct food vessel pottery at each stage.
Exactly how these shifts affected Ireland has been subject to debate. What caused the transitions? Were the new ways adopted locally or did they result from migrations?
Now, genetic studies offer new clues. By sequencing genomes directly from ancient people, scientists are able to carry out a type of genetic time travel that is showing us more about the past.
Clear evidence of migration
In this study, a team of geneticists from Trinity College, Dublin, in the Republic of Ireland, and archaeologists from Queen's University, Belfast, in Northern Ireland, sequenced the genome of four ancient Irish people.
One was an early farmer woman who lived near Belfast some 5,200 years ago; the others were three men from a later period, around 4,000 years ago in the Bronze Age, after the introduction of metalworking.
The findings show clear evidence for massive migration. The early farmer has a majority ancestry originating ultimately in the Middle East, where agriculture was invented. In the Bronze Age genomes, about a third of the ancestry can be traced to ancient sources in the Pontic Steppe.
The early farmer had black hair, brown eyes and was more similar to southern Europeans. However, the genetic variants circulating in the three Bronze Age men from Rathlin Island had the most common Irish Y-chromosome type, blue eye alleles.
The results in the three men also provide evidence of a C282Y mutation, the most important variant for hemochromatosis, a genetic disease is so frequent in people of Irish descent that it is sometimes referred to as a Celtic disease.
Study leader Dan Bradley, professor of population genetics in Trinity College Dublin, says:
"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. This degree of genetic change invites the possibility of other associated changes, perhaps even the introduction of language ancestral to western Celtic tongues."
Dr. Eileen Murphy, senior lecturer in osteoarchaeology at Queen's University Belfast, says the project shows how powerful ancient DNA analysis can be in answering long-standing questions about the origins of the Irish.
Lara Cassidy, also of Trinity, adds that there is a strong genetic affinity between the Bronze Age genomes and modern Irish, Scottish and Welsh. This, she says, suggests that central attributes of the insular Celtic genome were established some 4,000 years ago.
Medical News Today previously reported on genetic studies suggesting the black death existed far earlier than previously thought.