Legend has it that, while raiding England around 500 C.E., the Irish warlord Niall of the Nine Hostages took a young St. Patrick prisoner and brought him to Ireland. Historians disagree about whether Niall was really the kidnapper, but one thing is for certain: This ancient king went on to found the most powerful ruling dynasty in Irish medieval history, the Uí Néill (literally "descendants of Niall"). Now, a study reveals that this royal lineage may be imprinted in the genes of roughly a tenth of Irish men living today.
Although most of our genetic makeup comes from both parents, men inherit their Y chromosome exclusively from their fathers. As such, geneticists can trace paternal lineage by studying genetic markers on this chromosome. Small mutations creep in over generations, so the number of differences in the markers of any two men can reveal how long ago their common forefather lived. In 2003, a population study in East Asia discovered a set of Y chromosomes with very similar markers among men living in what had been the Mongol Empire. The scientists speculated that some 16 million men with these markers were all descendants of Genghis Khan (Science, 23 February 2003, p. 1179).
In the same spirit, geneticist Daniel Bradley and his colleagues from Trinity College in Dublin analyzed the Y chromosomes of 796 Irish men. Interestingly, quite a few shared the same markers--more than would be expected by chance. Looking for a historical explanation, the team realized that many of the men with this Y signature had family names that traced back to various offshoots of the Uí Néills. "Our research shows that these dynastic groups did have a common ancestor," Bradley says, thus providing a genetic underpinning to Ireland's rich genealogical tradition. This ancestor appears to have lived approximately 1700 years ago--consistent with the period of Niall's reign--the team reports 8 December in the American Journal of Human Genetics.
Some experts remain sceptical. Although the findings are compatible with the Niall hypothesis, geneticist Chris Tyler-Smith of the Wellcome Trust Sanger Institute in Cambridge, U.K., warns that the conclusion rests on uncertain assumptions about mutation rates and time between generations. He thinks the main significance of this work is that it shows--as did the earlier Genghis Khan study--how power and status can affect genetics. The Uí Néill Y chromosome owes its success not to a particular evolutionary advantage, he says, but rather to the fact that the high-ranking Uí Néill males in medieval Ireland could father many sons who later did the same.