The balance of probabilities is that the ‘Gerins/Guerins’ of Killaloe are most likely descendants of the Ó Géaráin sept of the Clan Culéin (the MacNamaras) of Co. Clare and are unconnected with the Huguenot name Guerin. The Ó Géaráin sept have been in Co. Clare since at least the late Middle Ages (1200); they are most likely an indigenous Thomond or north Munster family and possibly also the origin of the other pockets of Guerins to be found in south Munster – Cork and Kerry. Their relationship to the other Guerin names of Cos. Mayo, Down, and Longford, mentioned by Wulfe and McLysaght respectively, is less clear.

Since RC church records did not, in general, begin until the early 1800s and because the Ó Géaráin/Gerins of Killaloe were not registered landowners we are unlikely to be able to prove this conclusively by tracing individual ancestral line further back into the 18th and 17th centuries.

However manuscript/documentary evidence that members of the Ó Géaráin sept lived in pre-Huguenot times in that part of Clare bordering the Shannon or that by the early 1700s they had moved into the area, specifically O’Briensbridge, Killaloe and Scariff areas, would further add to the existing body of circumstantial evidence supporting the hypothesis of an Ó Géaráin origin for the Guerins of East Clare.

There may, nevertheless, be another solution to the problem with the help of modern medical science and DNA testing. It seems that DNA markers in the male line of descent can say conclusively whether any two males share a common male ancestor or not. Apparently there is no equivalent test yet for the female line.

To quote the example given in the relevant article, taken from the internet (pgtaylor@mail.btinternet.com); a copy of the article is included below.

“FOR INSTANCE, an American man with the O’Hanlon surname may have traced his ancestry back to Sean O’Hanlon who was born in Ireland, say, 250 years ago. He then might also find other living descendants of Sean O’Hanlon during the course of his genealogy search. The DNA test can provide conclusive support for this or, alternatively, exclude such a relationship. The method assesses genetic relatedness using molecular techniques alone; it therefore provides an independent assessment of relatedness that does not involve archive searches.”

It only remains to find a male Irish Guerin of genuine (genealogically proven) Gaelic O Géaráin descent who is willing to give a DNA sample for comparison! While a positive test here would be necessary to prove an O Géaráin ancestry, a negative result would not, of itself, be sufficient to prove a Huguenot ancestry. For this a further positive test against a male Irish Guerin of genuine (genealogically proven) Huguenot descent would be necessary.

http://archiver.rootsweb.com/th/read/GENMTD/1999-01/0915630392

GENMTD-L Archives

From: pgtaylor <pgtaylor@mail.btinternet.com>
Subject: DNA tests and patrilineal surname extinction
Date: Wed, 06 Jan 1999 05:46:32 -0800

I was interested by the discussion on extinction of surnames. I would appreciate comments on the use of the following method to address this issue. My overall point is that regardless of surname extinction and non-paternity in human male lineages, the Y chromosome and its genetic markers reveal the TRUE paternal lineage.

I posted the following message to soc.genealogy.marketplace yesterday.
I would like people's reaction to this proposal.

Message copied:

I am a molecular geneticist living in the UK. I have recently developed some novel techniques for testing whether men share a common ancestor centuries ago. The methods are at present unique and unrivalled (and peer reviewed by the scientific community) but not yet available to the wider public. The DNA test uses genetic markers on the human Y chromosome, so the test can only be done on males. However, all that is required from the presumed "relatives" is a few cheek cells (liberated by a simple salt/sugar mouthwash). No needles or blood are involved. Men who want to be tested should (normally) have the same surname (unless adoption is evident), must be living, and suspect that they share a common male ancestor some generations ago.

Here is an explanation by hypothetical example (with arbitrary names!):

FOR INSTANCE, an American man with the O’Hanlon surname may have traced his ancestry back to Sean O’Hanlon who was born in Ireland, say, 250 years ago. He then might also find other living descendants of Sean O’Hanlon during the course of his genealogy search. The DNA test can provide conclusive support for this or, alternatively, exclude such a relationship. The method assesses genetic relatedness using molecular techniques alone; it therefore provides an independent assessment of
relatedness that does not involve archive searches.

What I would like to know, from all the genealogy hobbyists out there, is whether anyone would be interested in using this DNA test if it were offered as a commercial service. Are there many potential customers out there? I would aim to make the service friendly, informative and accessible to all enthusiastic genealogists.

Please note however that DNA testing is still an expensive procedure; although I believe it would be competitive when compared to the total cost (in time and money) of classical genealogical search methods.

The tests are very accurate and improving all the time. A prototype version of the same technique was used to search for relatives of President Thomas Jefferson, though I concede that some of its conclusions and methods of data interpretation are controversial/debatable (See Foster et al. (1998). Nature. Vol. 396 pages 27-28. “Jefferson fathered slave’s last child”).
I do not personally agree with some of the conclusions, and I certainly did not choose the misleading title!
However, I have made considerable improvements to these methods of analysis since that notorious project.

Please be aware that (unfortunately) there are no similar tests available for female lineages that go back more than a few generations.
Please don’t contact me about this: it is a biological fact and there is currently no solution to it. Sorry about that.

So, to all serious genealogists out there, is there a market? Would you want to use this commercial DNA testing service as a part of your family tree research?

Paul G. Taylor (BSc, MSc, DIC)
Human Molecular Geneticist
United Kingdom

pgtaylor <pgtaylor@mail.btinternet.com>