UPDATED APRIL 2020. Approximately 66% of the present population of the Island of Ireland are descendants of ‘Native Irish Gaels' who were themselves a fusion of prehistoric and Celtic peoples who occupied the Island virtually uninterrupted until the Vikings arrived in 795 AD.

Medieval Irish society was intensely hierarchical, where status mattered, and where clear distinctions were drawn between Kings, Cleric, Poets and the free and un-free. It mattered who you were in early Irish society! It is no coincidence that Ireland  was the first European Country to adopt (from about 800 AD onwards) paternally inherited surnames, which were typically denoted by either 'Mac’ or 'O' meaning ‘son of’ or ‘grandson of' respectively. Surnames of this nature were a form of genealogy. They immediately informed strangers as to where you were from, and to whom your allegiances lay. These surnames are different from English surnames which typically denoted a persons profession e.g. Smith, Forrester, and Taylor, or where they lived or originated from e.g. Townsend, Hill, and York.

Even more amazing is that scientific research has revealed that most (if not all) of the estimated 1,500 distinct Irish Clans had a single founding male ancestor, that's 1,500 'Adams.' For example, research has shown that the surnames ‘Sullivan’ and ‘Ryan’ both have a single founding Ancestor, and that both those surnames are associated with a single geographical location. Scientific research has shown that after 1,200 years there is a 50% chance that each male is directly descended from their founding surname-Adam. The other 50% of males have acquired their surname through 'non-paternal' events (adoption/maternal transfer of a surname) that have occurred since their surname first appeared. However, some surnames are derived from common personal names which means that there were more than one surname-Adam for most surnames. For example, the Surname ‘McGuinness’ had at least 2 founding Adams which corresponds to 2 distinct Clans found geographically quite far apart. The Surname ‘Donohoe’ has at least 3 founding Adams representing at least 3 quite distinct clans found in separate parts of Ireland.

If you have taken a commercial ancestral Y-DNA test, and you have received your results detailing many dozens of unfamiliar surnames of people with whom you share a common male ancestor, you may well (like me) have asked yourself; 'How can I match males with different surname?' The answer is quite simple. Those surnames are a snapshot of your male ancestors relatives and neighbours from about 1,000 years ago (the approximate time when surnames were first used). For example, my own closest genetic matches are with people named 'Bowe/Bowes,' ‘Carroll,’ 'Flanagan,' 'Purcell' and ‘Dooley.’ When one plots where those surnames occur together with many other surnames that appears as Y-DNA matches are in County Laois in Ireland. County Laois is where my ancestor was living when he first took his surname. Put simply, although my founding-Adam ancestor took the surname 'Bowe,' his distant relatives who lived close by, took the surnames Carroll, Flanagan, Purcell and Dooley.' Hence, Irish Origenes can examine the surnames revealed in your Y-DNA test and pinpoint where in Ireland your Adam lived. If your ancestors were there 1,000 years ago, they were probably there for 100’s if not 1,000’s of years before that and their descendants (and your distant relatives) still live there today. 

Anybody interested in the Science of Surnames should read:

Using Y Chromosome DNA testing to Pinpoint a Genetic Homeland. Dr Tyrone Bowes 2013 (click here to download).

A Y-chromosome signature of hegemony in Gaelic Ireland. Moore LT, McEvoy B, Cape E, Simms K, Bradley DG. Am J Hum Genet. 2006 Feb;78(2):334-8.

The scale and nature of Viking settlement in Ireland from Y-chromosome admixture analysis. McEvoy B, Brady C, Moore LT, Bradley DG. Eur J Hum Genet. 2006 Dec;14(12):1288-94.

Y-chromosomes and the extent of patrilineal ancestry in Irish surnames. McEvoy B, Bradley DG. Hum Genet. 2006 Mar;119(1-2):212-9.

In the name of the father: surnames and genetics. Jobling MA.Trends Genet. 2001 Jun;17(6):353-7.

Y-chromosome variation and Irish origins. Hill EW, Jobling MA, Bradley DG. Nature. 2000 Mar 23;404(6776):351-2.