Saturday, 26 December 2020

The Big Y & Irish Clan Research

There has been increasing interest in Irish Clan Research as more fine-detailed Y-DNA data becomes available and the Irish branches of the Tree of Mankind have grown larger and sprouted more downstream branches. Soon we should be able to identify specific DNA signatures for particular Irish clans. This has already happened with the Uí Neill (O'Neill) in northwest Ireland and the Dál gCais (ancestors of Brian Boru) in Clare & Limerick. The discovery of the burial site of Red Hugh O'Donnell has also created a lot of media buzz (as discussed in a previous post).

The usual test to start with is the Y-DNA-37 test from FTDNA. Only men can do this because women do not have a Y chromosome. So you will need to find the appropriate male relative to test. The more upscale test is the Big Y test and this tells us very specifically on which branch of the Tree of Mankind you sit. This is the most valuable test for Irish Clan Research.

So if you want to help further this type of research, find your surname project (just google: FTDNA & your surname), discuss testing options with the Project Admin (their email will be on the project's home page), and decide whether you want to start with the Y-DNA-37 or go straight for the Big Y test. The tests are frequently discounted in the many sales that occur throughout the year (the screenshot below is from the Christmas Sale 2020).

Here is a detailed step-by-step breakdown of the various options ...

Step 1. Have you done a Y-DNA test at FTDNA already? 

If no, read below. If yes, go to the next step.

  1. go to the FTDNA website & scroll down until you get to the 3 test types (see screenshot above)
  2. choose the test you want and click on the ORDER NOW button. You may wish to start with the usual starter test (Y-DNA-37) or you may wish to go for broke and order the top of the line test (the Big Y-700). You may want to discuss the pros & cons with the relevant Project Administrator (see Step 2 below)
  3. after you have ordered the test, find the project you want to join (google: FTDNA & your surname), click on the JOIN button in the photo on the project's main page, and follow the instructions (the example below is from the O'Donnell DNA Project)

  4. If you have a coupon code for an additional discount off the price of your test, follow the instructions below ... 
a) click on “Coupon Code” when you get to the Shopping Cart screen…

b) enter the code in the Coupon Code box that appears

c) click on Apply and you will see the price drop ... then click on Proceed to Checkout

Step 2. Are you a member of the relevant Clan Project?

If no, read below. If yes, go to the next step.

  1. find the project you want to join (google: FTDNA & your surname), click on the JOIN button in the photo on the project's main page, and follow the instructions (the example above is from the O'Donnell DNA Project)
  2. if you have questions, email the Project Admin for advice & guidance. Their email is on the project's Main Page.

Step 3. Have you or one of your close relatives done the Big Y test?

If no, read below. If yes, go to the next step.

    1. Sign in to your FTDNA account
    2. click on ADD ONS & UPGRADES at the top right of your main page (see screenshot below)
    3. Scroll down to the Big Y-700 test and click on the ORDER NOW button
    4. If you have a coupon code for an additional discount off the price of your test, follow the instructions in Step 1.4 above 

    Step 4. Is your version of the Big Y test the Big Y-500?

      If no, read below. If yes, go to the next step.

        1. the Big Y-500 test was upgraded in Jan 2019 to the Big Y-700 test, which provides a lot more information than the previous version. There is a good blog post about it here.
        2. You can check which version of the Big Y test you have done by hovering over your name (top right) & clicking on ORDER HISTORY (see screenshot below).
        3. If you have only done the Big Y-500, discuss with your Project Administrator about the value of upgrading it to the Big Y-700 test. It may be helpful ... it may be not.
        4. If you have a coupon code for an additional discount off the price of your test, follow the instructions in Step 1.4 above 

        Step 5. Have you uploaded your Big Y data to the Y-DNA Warehouse?

          If no, read below. If yes, you're good! You have optimised the value you will get from your Big Y test.

          1. The Y-DNA Warehouse is a repository for Big Y data. It allows researchers to use the data to help advance many types of research, including Irish Clan Research. Appropriate safeguards are taken to protect your data and your privacy. Full details can be found in the Data Policy section here (scroll down to the end of the page).
          2. Instructions for uploading your Big Y data can be found here.

            Remember, the volunteer Project Administrators are a great source of information, so never hesitate to drop them an email with any questions you may have.

            With a bit of luck, you may find that you have a direct genetic connection to one of the major Irish Clans.

            Maurice Gleeson
            Dec 2020

            Tuesday, 11 August 2020

            Digging up your Ancestors - Citizen Science meets Ancient DNA

            There have been major advances in recent years in the field of Ancient DNA. The science has evolved to the point where the DNA profile extracted from ancient bones can be linked directly to surname projects at FamilyTreeDNA. This is particularly relevant to Irish surname projects and is sparking a renewed interest in medieval Irish history and Irish Clan research. But what is the optimal way of connecting Ancient DNA to Citizen Science? Read on!

            Dutch Water Color Painting of Irish Men and Women, about 1575
            (from Wikimedia Commons)

            Y-DNA and Citizen Science

            Y-DNA has been used for paternity testing and forensic cases since the 1980s but it was only with the advent of direct-to-consumer DNA testing by FamilyTreeDNA (FTDNA) in the early 2000s that saw Y-DNA being used in surname research (Y-DNA and surnames both follow the father's father's father's line). There are now over 10,000 group projects at FamilyTreeDNA, connecting people to their surname origins and in some cases a Clan history. You can find out if there is a project for your surname by simply googling: FTDNA & "your surname".

            Many projects have now reached an advanced state of maturity and have helped characterise the number of distinct genetic groups associated with a particular surname, how old each genetic group is, where it came from geographically, and whether or not it is associated with a particular Clan (Irish or Scottish).

            These projects are run by volunteer Administrators who help project members with their questions, collate & analyse the project data, and publish their results & conclusions. This is a great example of Citizen Science in action. The output from these projects has greatly accelerated the construction of the Tree of Mankind (Y-Haplotree) and the Tree of Womankind (mitochondrial Haplotree) to the extent that the ongoing construction of these trees has passed from the Academic Scientists to the Citizen Scientists.

            The Rapid Evolution of Ancient DNA Research

            Ancient DNA hit the headlines with the discovery of the remains of Richard III in 2012. DNA played a crucial role in his identification and the story captured the public imagination. Project Administrators discussed the possibility of using Ancient DNA within their surname projects. The Barrymore project was an early attempt to link ancient DNA to a specific surname project at FamilyTreeDNA. 

            From The Guardian, 4 Feb 2013

            More recently, advances in testing ancient DNA is producing exciting results about Ireland’s ancient past that is rewriting the history books. The Ancient DNA Lab at Trinity College Dublin has DNA tested over 100 ancient Irish samples collected over the last 200 years by intrepid archaeologists and antiquarians, and lying in wait in museum storerooms all over Ireland. These samples date from 6000 years ago up to medieval times. The first publication from this group was in 2015 and made news headlines across the world. [1,2] It completely upended long-established theories of “Celtic” origins for the Irish and showed that the modern Irish genome is substantially pre-Celtic. Since then testing ancient Irish DNA has progressed at a furious pace and further publications from this ground-breaking work are continuing to emerge. The most recent revealed evidence of an elite dynasty at the Newgrange passage tomb some 5000 years ago. [3,4] 

            Ancient DNA testing is now being applied to samples from the last millennium - in other words, within the surname era. In 2016, a road-widening scheme uncovered the site of a medieval community in Ranelagh, Co. Roscommon, which was occupied from about 500 to 1100 AD. Almost 800 skeletal remains have been found and DNA analysis of some of these is progressing. This major discovery will tell us a lot about life in medieval Ireland, how our ancestors lived, and how they died. We may even be able to link some of these medieval individuals to specific Irish Clans and even surnames, thanks to the multitude of people who have had their Y-DNA tested at FamilyTreeDNA (over 750,000).

            The medieval ring fort at Ranelagh
            (from The Irish Examiner)

            Then in May 2020, Spanish archaeologists found the site of the old chapel in Valladolid where Irish prince Red Hugh O'Donnell was buried in 1602. They located the chapter, and discovered several intact skeletons. [8] It was anticipated that identification of Red Hugh would be facilitated by the absence of his two big toes which were amputated due to frostbite following a daring escape from Dublin Castle across the Wicklow Hills. However, apparently many of the skeletons discovered were missing their feet and thus identification may have to rely heavily on DNA testing of all the skeletons and comparison of the resulting DNA profiles with those of living relatives with genealogically-established pedigrees. The O'Donnell DNA Project at FamilyTreeDNA will also help in this regard.

            The archaeological dig discovered 16 skeletons in the Chapel of Marvels at Valladolid, Spain 
            (photo: Jonathan Tajes from El Día de Valladolid website)

            It is highly likely that similar discoveries will be made over time and other examples of ancient DNA that falls within the surname era will emerge. Comparing this ancient DNA against the DNA of living people who have volunteered for surname projects and other group projects at FamilyTreeDNA will potentially allow these ancient individuals to be identified by surname and by Clan affiliation. And that will add considerably to the value of the academic research as well as advancing the aims of Surname DNA Projects run by Citizen Scientists. 

            But what kind of DNA extraction, testing and comparison needs to be done in order to optimise the chances of a successful outcome?

            Ancient DNA analysis

            There are no set standards for the retrieval and analysis of Ancient DNA, but recent projects have applied the following techniques and methods:

            1) Getting the tissue sample

            When ancient remains are excavated, one of the first questions faced by the project team is which bone to use to obtain a tissue sample for DNA testing. Bone tissue sampling from the petrous part of the temporal bone in the skull appears to offer the highest chances of success. This is the densest bone in the human body and, in ancient samples, the yield of human DNA from this bone is usually higher than elsewhere (e.g. molar teeth, other bones). There is also less risk of contamination by DNA from soil bacteria. Kendra Sirak at UCD (University College Dublin) has devised a technique of sampling the bone from inside the skull and this causes less bone destruction. For the identification of the remains of Irish rebel Thomas Kent in 2016, Jens Carlsson described how he and his team discarded the first third of the sample, analysed the middle third, and kept the last third for any future additional analyses.

            2)  Testing the extracted DNA

            Once the tissue sample has been obtained, the next step is to extract DNA from it (if possible). If there is a sufficient sample of DNA extracted, Whole Genome Sequencing (WGS) would be the test of choice. This provides all 3 types of DNA (Y-DNA, mitochondrial DNA, and autosomal DNA) and both types of DNA marker (STR & SNP markers). Coverage of the genome can be quite good - two of the first 4 ancient genomes sequenced in Ireland achieved 10-11x coverage. [1] WGS can also achieve high quality DNA data that is optimal for comparison against reference samples, including the types of test used by the commercial direct-to-consumer companies as well as standard forensic tests. 

            One of the major advantages of WGS is that it assesses 3 billion points on the human genome. In comparison, standard forensic tests only analyse about 17 DNA markers. That's 17 vs 3,000,000,000 - a huge order of magnitude difference. And that difference is associated with a huge jump in the quality of the information that can be gleaned from the data. 

            Similarly, commercial DNA tests also analyse many more markers than forensic tests - commercial autosomal DNA tests assess >600,000 markers (compared to 17 in the standard forensic autosomal tests, which use STRs) and Y-DNA testing assesses up to 851 STR markers (compared to up to 23 STR markers with forensic Y-DNA tests). In addition, forensic Y-DNA tests do not assess Y-DNA SNP markers whereas commercial Y-DNA tests (like FTDNA's Big Y test) assesses >200,000 SNP markers. Again, the quality of the information that can be extracted from these commercial Y-DNA tests is far superior to that associated with standard forensic Y-DNA tests.

            As an alternative to WGS, chip-based technologies are being developed (e.g. at David Reich's lab in Harvard, Connecticut). These would assess about 1.2 million autosomal SNP markers (compared to the 17 autosomal STR markers used in standard forensic tests).

            Summary of Process of Extraction of Ancient DNA
            (from my YouTube video)

            As far as relative-matching is concerned, the type of relationship that can be identified with standard forensic autosomal DNA tests extends only as far as parents, siblings, aunt/uncle, and niece/nephew, but cannot go beyond this with any degree of reliability. This is an important consideration if we hope to identify any of the remains of the 800 children believed to be buried at Tuam. In contrast, commercial DNA tests can reliably identify much more distant cousins, extending out to 4th cousins or greater.

            Forensic Y-DNA tests are very limited in their ability to group people into distinct genetic groups or place someone on the Tree of Mankind. In contrast, commercial Y-DNA tests (like the Big Y) are routinely used in Surname DNA Projects at FamilyTreeDNA  help group people into well-defined genetic groups with a common ancestor within a genealogical timeframe (the last 1000 years), and place people very precisely on the Tree of Mankind. In relation to ancient DNA, this could help identify a person's surname and potentially a Clan affiliation - something that would be relevant with regards to the identification of Red Hugh O'Donnell, for example.

            Thus WGS or chip-based tests would provide considerably more information than standard forensic tests and WGS should be the first choice when it comes to testing. However, the big disadvantages of WGS are a) cost and b) the need to utilise a much larger sample of DNA than is needed for standard forensic tests. So practicalities may dictate whether or not WGS is possible. Nevertheless, it should be the test of choice for ancient DNA analysis.

            3) Comparing the Ancient DNA to reference samples

            Any DNA extracted from ancient remains can be compared against targeted individuals (e.g. as was the case for Richard III, and the WWI soldiers from Fromelles - see video here) or against a more general population in a genetic genealogy database (such as GEDmatch or FTDNA) or even a forensic database (such as CODIS). In 2018, the new science of Investigative Genetic Genealogy was created and since then, the GEDmatch and FTDNA databases have been widely used to solve "cold cases" involving violent crime as well as identify unknown human remains. To date, over 100 cases have been solved.

            Y-STR data could be compared directly against the STR data on the public Results Page of specific Surname Projects. For example, the O'Donnell project's STR data could be used to help identify the remains of Red Hugh O'Donnell. 

            Y-SNP data could be compared against the available public Y-haplotrees such that the individual could be placed on a specific branch of the Tree of Mankind. This could help identify a likely surname for the individual (if the remains were <1000 years old) as well as an association to a specific Irish Clan. Of the available Y-Haplotrees, the most comprehensive is FTDNA's Big Y Block Tree which is available only to FamilyTreeDNA customers. However, they also maintain a public Y-Haplotree which can be used in conjunction with the Big Tree (for associated surnames and country origins) and YFULL's Y-Haplotree (for crude dating of branches).

            Using the example of Red Hugh O'Donnell again, based on SNP testing undertaken by the members of the O'Donnell DNA Project, it is anticipated that Red Hugh will carry the SNP marker BY21154. Below is the SNP Sequence for BY21154. A SNP Sequence is simply the sequence of SNP markers that characterises each branching point on the Tree of Mankind starting "upstream" at the level of the Haplogroup (R in this case) and progressing all the way "downstream" (i.e. towards the present day) to the Terminal SNP. Think of this string of SNPs as a line of ancestors coming forward in time towards the present day. Comparing the SNP Sequences of two branches helps us see exactly where each branch sits on the Tree of Mankind relative to each other and this tells us how closely or how distantly related are people sitting on these respective branches. The SNP Sequence for BY21154 is:
            • R-L21 >>> M222 > S658 > DF104 > DF105 > DF85 > S673 > S668 > DF97 > ZZ36 > FGC19851 > Z29319 > BY35773 > BY21154
            Age estimates for this SNP marker are available on the YFULL website here and surnames on adjacent branches of the Tree of Mankind can be viewed on the Big Tree here

            If Red Hugh does test positive for this SNP marker, then anyone else with this marker is in some way related to Red Hugh O’Donnell (via one of his direct male line ancestors - he had no descendants himself). This allows living people to connect directly with their O’Donnell ancestry and the history of the O’Donnell Clan in a very tangible way.

            Furthermore, DNA testing of ancient remains of known historical figures will help to confirm or refute the veracity of the ancient Irish annals and genealogies. We are seeing a lot of data from group projects at FamilyTreeDNA that supports the veracity of some genealogies and other data that suggests the opposite. Adding the DNA of known historical figures to the mix will help further this research. 

            This is a very exciting time for genetic genealogy as we explore the synergies between Ancient DNA analysis and Citizen Science. The rapid advances in these modern techniques are helping to enhance our understanding and appreciation of our ancient heritage.

            I can’t help feeling that Red Hugh would approve.

            Maurice Gleeson
            Aug 2020

            Resources and Links

            1) Neolithic and Bronze Age migration to Ireland and establishment of the insular Atlantic genome. Cassidy et al. PNAS 2016, 113 (2) 368-373. Available at
            2) Man’s discovery of bones under his pub could forever change what we know about the Irish. Peter Whoriskey, The Independent, 17 March 2016. Available at
            3) A Genomic Compendium of an Island (2017) Lara M. Cassidy, PhD thesis, Smurfit Institute of Genetics, Trinity College Dublin.
            4) A dynastic elite in monumental Neolithic society. Cassidy, L.M., Maoldúin, R.Ó., Kador, T. et al. Nature 582, 384–388 (2020).


            Friday, 17 April 2020

            Statistical Analysis of Irish Type III signature

            Chi-squared test on Irish Type III Analysis

            Dennis Wright’s paper from 2009 describes a four-fold greater frequency of the Irish Type III (IT3) signature among Dalcassian surnames compared to non-Dalcassian surnames …

            This data is summarised in Tables 7 and 8 of the paper.

            Thus, among men with Dalcassian surnames, 57 had the IT3 signature and 214 did not. Similarly, among men with non-Dalcassian surnames, 37 had the IT3 signature and 334 did not.

            Chi-square test

            I put these values into the 2x2 contingency table that forms part of the chi-square calculator at

            The contingency table below provides the following information: the observed cell totals, (the expected cell totals) and [the chi-square statistic for each cell].

            The chi-square statistic, p-value and statement of significance appear beneath the table. Blue means you're dealing with dependent variables; red, independent.

            Marginal Row Totals
            57   (39.68)   [7.56]
            214   (231.32)   [1.3]
            37   (54.32)   [5.52]
            334   (316.68)   [0.95]
            Marginal Column Totals
            642    (Grand Total)

            The chi-square statistic is 15.3283. The p-value is .00009. This result is significant at p < .01.

            The chi-square statistic with Yates correction is 14.4561. The p-value is .000143. Significant at p < .01. 
            (There's probably a consensus now that the correction is over-cautious in its desire to avoid a type 1 error, but the statistic is there if you want to use it).

            If we analyse only those Dalcassian surnames in bold in Table 7, we get the following results:

            Marginal Row Totals
            51   (22.04)   [38.03]
            73   (101.96)   [8.22]
            37   (65.96)   [12.71]
            334   (305.04)   [2.75]
            Marginal Column Totals
            495    (Grand Total)

            The chi-square statistic is 61.7173. The p-value is . This result is significant at p < .01.

            The chi-square statistic with Yates correction is 59.6042. The p-value is . Significant at p < .01.

            Fisher Exact Test

            I also used another calculator on the website to do a Fisher Exact Test …

            The Fisher exact test statistic and statement of significance appear beneath the table. Blue means you're dealing with dependent variables; red, independent.


            Marginal Row Totals
            Marginal Column Totals
            642  (Grand Total)

            The Fisher exact test statistic value is 0.0001. The result is significant at p < .01.

            If we analyse only those Dalcassian surnames in bold in Table 7, we get the following results:


            Marginal Row Totals
            Marginal Column Totals
            495  (Grand Total)

            The Fisher exact test statistic value is < 0.00001. The result is significant at p < .01.


            Both the chi-square test and Fisher exact test confirm that all comparisons are statistically significant, with p < 0.01 for all comparisons.

            Maurice Gleeson
            April 2020

            Thursday, 16 April 2020

            When were surnames introduced to Ireland?

            The short answer is: about 1000 years ago, but ...

            And that "but" represents the fact that different Irish surnames arose at different times, usually between 900 to 1350 AD, and mostly between 950-1150 AD, with the busiest period being 1000-1050 AD. Also, surnames with the prefix O or Ó were formed prior to 1200 AD and those that formed afterwards were mainly those with the prefix Mac. These are the top-line conclusions from the data analysis that follows.

            Back in 1923, Woulfe claimed that "Irish surnames came into use gradually from about the middle of the 10th to the end of the 13th century". [1] But let's look at some of the hard evidence supporting this statement. I have gathered such data from two sources - the introduction to the 1923 edition of Woulfe's Irish Names and Surnames [1] and a more recent 1999 journal article by Ó Murchada. [2]

            In his 1999 review article, Ó Murchada provides a table in the appendix with years of death for 78 progenitors of a selection of Irish surnames. [2] The complete list of 78 surnames is included in Footnote 1.

            Ó Murchada suggests that the average surname would have come into use during the time of the progenitors' great-grandsons.
            Using Corpus Genealogiarum Hiberniae as source, I extracted thirty genealogies which could be traced in the annals and dated for at least ten generations. This gave a total of 416 generations, which when divided into a total of 13,779 years, furnished an average generation gap of 33.2 years, i.e. the number of years between the death of a father and that of his son / successor ... By my calculations, adding sixty-six years to the date of death of the eponym will give an approximate date for the death of his grandson, and at any time subsequent to that, in his great-grandsons era, one could expect the surname to have come into use ... (Ó Murchada p30)
            Adding 66 years to the year of death of the progenitor to arrive at the approximate date of surname introduction seems like a reasonable approach. Woulfe takes a similar strategy by adding 60 years to the date when the progenitor flourished, died or was slain (see below). [1] This approach is supported by specific examples from the list of surnames.

            The earliest surname (O Clery) is probably the first fixed surname to be used in Europe. The originator died in 858 AD and the first record of its use is 58 years later in 916 AD in the Annals of the Four Masters. A second occurrence of this fixed surname occurs 34 years later in 950 AD. [1]

            Woulfe gives other examples of specific dates when several fixed surnames were first mentioned in the ancient texts, illustrating that inherited fixed patronymic surnames were well-established before the turn of the first millennium. [1]
            • Ó Canannáin (O'Cannon) ... 941 (he "flourished" in 950 AD so this surname appears to have been introduced during the lifetime of the progenitor. In the ancient texts, "flourished" simply means lived, indicated by the Latin word floruit, or the abbreviation fl.)
            • Ua Néill (O'Neill) ... 943 (the progenitor was slain in 919)
            • Ua Ruairc (O'Rourke) of Breifney ... 952 (progenitor died in 893)
            • Ua Ciardha (O'Keary) of Cairbre ... 952
            • Mag Aongusa (Maguiness) ... 956
            • Ó Maoldoraidh (O'Muldory) of Tirconnaill ... <999 (progenitor flourished in 870)
            • Ó Dubhda (O'Dowd) of Tireragh ... <999 (progenitor flourished in 876)
            • Ó Ceallaigh (O'Kelly) of Ui Maine ... <999 (progenitor flourished in 874)

            This data also disproves the mistaken belief that surnames were introduced by Royal Decree during the reign of Brian Boru (1002-1014). In fact the O'Brien surname (which derived from Brian's name) did not become a fixed inherited surname until the time of his grandsons. [1]

            Note that it was not uncommon for the same surname to arise in different places and hence the clan territory is frequently added after the surname as a qualifier. For example, we have the O'Donnell clan of Corca Bhaiscinn, another of the same name in Ui Maine, and a third in Tirconnell. And there was also the O'Conor clan of Connacht, another in Corcomruadh, and a third clan in Offaly.

            So, adding up the various dates of surname introduction in Ó Murchada's article and dividing by 78 gives an average date of 1072 AD for the introduction of surnames in Ireland. As we can see in the bar chart below, the majority of the surnames were introduced between 950 and 1150 AD (59/78 = 76%), with the time period 1000-1049 being the busiest for surname introduction.

            Estimated dates of surname introduction for 78 Irish surnames - data extracted from O'Murchada 1999 [2]

            A similar pattern is seen with the data extracted from Woulfe. [1] In the Introduction to the hard copy of his Irish Names and Surnames (page xvi), Woulfe lists 46 surnames that had previously been compiled by O'Donovan and extracted mainly from from the Annals of Ulster and the Annals of the Four Masters. The list (see Footnote 2 below) includes dates when the various progenitors flourished, died or were slain.

            Woulfe states that the date when the surname became fixed "cannot have been more than 60 years from the period when the ancestor flourished or died". However, in an attempt to standardise the dates, I have added an additional 10 years to any dates when they "flourished" (to give an approximate date of death or manslaughter) and then added 60 years on top of this. This gives an average of 66 years between the death of the progenitor and the introduction of the surname ... which is the same interval employed by Ó Murchada above.

            Based on these adjustments, the average year for the introduction of these 46 surnames was 1048 AD. The earliest was 920 AD and the latest was 1350 AD. The largest number of surnames appeared in the period between 1000-1049 AD with 83% (38/46) of surnames being introduced between 950-1150 AD.

            Estimated dates of surname introduction for 46 Irish surnames - data extracted from Woulfe 1923 [1]
            (based in turn on O'Donovan)

            Combining the two datasets and removing any duplicates (or likely duplicates) produced 109 distinct surnames (see Excel spreadsheet here). The average year of introduction of surnames was 1068 AD (range 920-1350) but the busiest period for surname introduction was again 1000-1049 AD. The majority of surnames (84/109= 77%) were introduced in the period between 950-1150 AD.

            The proportion of surnames introduced in successive centuries is as follows:
            • 10th Century ... 24/109 = 22%
            • 11th Century ... 50/109 = 46%
            • 12th Century ... 26/109 = 24%
            • 13th Century ...   7/109 =   6%
            • 14th Century ...   2/109 =   2%

            Estimated dates of surname introduction for 109 Irish surnames - combined dataset

            In the combined dataset, surnames prefixed with O or Ó arose between 920 and 1193 AD, and surnames prefixed with Mac between 955 and 1350 AD (as illustrated in the bar chart below). The prefix Mac means "son of" and O or Ó means "grandson of" or alternatively "descendant of".

            Interestingly, O surnames were introduced about 124 years earlier than Mac surnames (1032 vs 1155 AD for average dates of introduction). Woulfe states that the creation of surnames with the O or Ó prefix "had almost certainly ceased" prior to the Norman Invasion, and that surnames that arose thereafter were primarily of the Mac variety. This is almost true - in the combined dataset, only two O surnames arose after 1169 AD (the start of the Norman Conquest); one in 1170 (O'Shaughnessy) and another in 1193 (O'Growney) - see Excel spreadsheet here.

            Estimated dates of emergence of O and Mac surnames - combined dataset

            This data paints a very clear picture of the emergence of surnames in Ireland.

            But from a genetic genealogy perspective, why is this important? Knowing when a particular Irish surname was first introduced will be of particular use to Surname Project Administrators as it identifies a maximum age for the genetic group that is presumed to be descended from that particular surname founder. This upper age limit can help constrain the date calculations for the various branches in this portion of the Tree of Mankind, including those branches below the overarching SNP for the surname in question, as well as the adjacent branches of different but genetically-related surnames.

            However, the data presented above does not answer the questions: when did surnames in Ireland become commonplace? when were they adopted by the majority of the population?

            And that is a topic for a subsequent article.
            Maurice Gleeson
            April 2020


            [1] Woulfe, Patrick. Sloinnte Gaedheal is Gall: Irish Names and Surnames (1923 Dublin), pages xv-xx. Online version available at

            [2] The Formation of Gaelic Surnames in Ireland: Choosing the Eponyms by Diarmuid Ó Murchadha, Locus Project, University College, Cork. Nomina (1999) - available at

            1) 78 surnames from Ó Murchadha [1] above ...

            2) 46 surnames from Woulfe [2] above ...