Population genetics, principally using Y-chromosome and mitochondrial deoxyribonucleic acid (DNA), has provided many novel insights into Ireland's past. These inlcude broad issues of early time-frame including the origin of the first Irish 9000 years before present, as well as the population impact associated with later events such as the appearance of Celtic culture and the Viking invasions. Furthermore, the Y-chromosome in combination with surname information has also allowed questions of more recent nature and smaller scale to be addresssed including the levels of patrilineal kinship in early medieval Irish kingdoms and the origin and subsequent history of Irish surnames themselves.