“Its offshoot I2a2a1a1a1a (S7753) includes men of several surnames of Irish Gaelic origin, such as McGuinness, Callahan, McConville and McManus, indicating that S7753 arrived in Ireland before the development of surnames. The estimated date of the haplogroup is around AD 500, which makes a neat fit to the earliest reference to the Cruithin in AD 552 (see p. 169).41 84 Tree of Y-DNA haplogroup I2a2a1a1 (M284).”