11"Medieval Irish Warlord Boasts Three Million Descendants." The New Scientist. Web. 12 June 2012. <http://www.newscientist.com/article/dn8600-medieval-irish-warlord-boasts-three-million-descendants.html>.
From the story: "The study says the chromosome has also been found in 16.7% of men in western and central Scotland and has turned up in multiple North American population samples, including in 2% of European-American New Yorkers...Though medieval Ireland was Christian, divorce was allowed, people married earlier and concubinage was practised. Illegitimate sons were claimed and their rights protected by law...As in other polygamous societies, the siring of offspring was related to power and prestige...one of the O'Neill dynasty chieftains who died in 1423 had 18 sons with 10 different women and counted 59 grandsons in the male line."
Another scientist, Ugo Perego, a senior DNA researcher at Sorenson Molecular Genealogy Foundation, determined that Mormon prophet Joseph Smith Jr. was definitely descended from Niall (http://www.genealogyblog.com/?p=8663).