Researchers Trace Roots of Irish and Wind Up in Spain
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By NICHOLAS WADE
For any observer of last week's St. Patrick's Day celebrators who wondered where all those Irish came from, science has provided an unexpected answer: Spain.
Using ancient Irish surnames and DNA analysis, researchers at Trinity College in Dublin have developed evidence that Irish men in Connaught, a western province of Ireland, are almost all descended from a population of hunters and gatherers who inhabited Ireland before the invention of agriculture.
Archaeologists believe the inventors of agriculture migrated from their homeland in the Near East, starting about 9,500 years ago, and gradually spread across Europe, displacing the existing inhabitants or intermarrying with them.
Dr. Daniel G. Bradley and colleagues at Trinity analyzed a DNA signature that was assumed to belong to the first inhabitants. In terms of the percentage of the population that carries the signature, there is a gradient across Europe, from 2 percent in Turkey to 63 percent in Britain to 78 percent in Ireland as a whole, as if reflecting the degree of mixing between Europe's ancestral hunters and gatherers and the farming invaders from the east.
The signature, a set of variations in the usual DNA sequence, is carried on the Y chromosome, which is bequeathed unchanged from father to son. Since surnames are inherited the same way Y chromosomes are in Ireland, Dr. Bradley measured the commonness of the DNA signature in Irish men with surnames known to originate in the north, south, east and west of Ireland.
He and his colleagues report in today's issue of the journal Nature that the DNA signature gradient continues within Ireland, with 98 percent of Connaught men, on the west coast, carrying the signature.
From genetic variations within the signature, Dr. Bradley estimates the Irish versions of it stemmed from individuals who lived 4,000 or more years ago. Ireland is believed to have been inhabited for 9,000 years, so Irish men who carry the signature could well be descendants of their country's very first occupants.
"It seems that in our extreme west of Ireland we have a snapshot of what western Europe was like before farming," Dr. Bradley said.
But where did those first hunter-gatherers come from?
The first carriers of the ancestral European DNA signature are estimated to have lived some 30,000 years ago and presumably were among the earliest modern human occupants of the continent after the Neanderthals were driven out. Outside of Ireland, the signature is most common in the Basque country of northern Spain, where 89 percent of men carry it.
In the last ice age, which lasted in Europe until around 10,000 years ago, Spain was a refuge for many plants and animals that recolonized Europe as the glaciers retreated. Dr. Bradley believes people may have done the same.
"They may have peopled this part of Europe by coming up from Spain," he said.
Dr. Bryan Sykes, a human geneticist at the University of Oxford in England, said he had traced a similar pattern of gene flow, from Spain through Brittany, Ireland and the west of Scotland. People of the Mesolithic period -- the Middle Stone Age -- were apparently taking a sea route from southern Europe's warm refuges as the glaciers retreated.
The geneticists are not the first to link the Irish with Spain. A Celtic legend says that the sons of a man named Milesius arrived in Ireland from Spain 1,000 years before the birth of Christ.
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