have Irish forebears, making the Irish diaspora one of the largest of any nation. Historically, emigration from Ireland has been the result of conflict, famine and economic issues. People of Irish descent are found mainly in English-speaking countries, especially Great Britain, the United States, Canada, New Zealand and Australia. There are also significant numbers in Argentina, Chile, Colombia and Brazil. The United States has the most people of Irish descent, while in Australia those of Irish descent are a higher percentage of the population than in any other country outside Ireland. Many Icelanders have Irish and Scottish Gaelic forebears. Origins and antecedents Prehistoric and legendary ancestors During the past 33,000 years, Ireland has witnessed different peoples arrive on its shores. Pytheas made a voyage of exploration to northwestern Europe in about 325 BC, but his account of it, known widely in Antiquity, has not survived and is now known only through the writings of others. On this voyage, he circumnavigated and visited a considerable part of modern-day Great Britain and Ireland. He was the first known scientific visitor to see and describe the Celtic and Germanic tribes. The terms Irish and Ireland are probably derived from the goddess Ériu. A variety of tribal groups and dynasties have inhabited the island, including the Airgialla, Fir Ol nEchmacht, Delbhna, the mythical Fir Bolg, Érainn, Eóganachta, Mairtine, Conmaicne, Soghain, and Ulaid. In the cases of the Conmaicne, Delbhna, and perhaps Érainn, it can be demonstrated that the tribe took their name from their chief deity, or in the case of the Ciannachta, Eóganachta, and possibly the Soghain, a deified ancestor. This practice is paralleled by the Anglo-Saxon dynasties. One legend states that the Irish were descended from the Milesians, who supposedly conquered Ireland around 1000 BC or later. Genetics Haplogroup R1b is the dominant haplogroup among Irish males, reaching a frequency of almost 80%. R-L21 is the dominant subclade within Ireland, reaching a frequency of 65%. This subclade is also dominant in Scotland, Wales and Brittany and descends from a common ancestor who lived in about 2,500 BC. According to 2009 studies by Bramanti et al. and Malmström et al. on mtDNA, related western European populations appear to be largely from the neolithic and not paleolithic era, as previously thought. There was discontinuity between mesolithic central Europe and modern European populations mainly due to an extremely high frequency of haplogroup U (particularly U5)