The Irish: Endogam-ish

When you hear the term endogamy, what communities come to mind? French Canadians, Puerto Ricians, Mennonites, Pacific Islanders, and Ashkenazi Jews are common examples. Some of these examples are from island peoples, so what about the Irish? 

Last time, I discussed the effect of a clearly endogamous community, Ashkenazi Jewish (AJ), on a relatively non-endogamous community, German, within my dad’s match list. My dad has more AJ matches with longer segments (greater than 20 cM), than expected at MyHeritage.com. I learned that even though my dad shares these longer segments, that most of his AJ matches probably do not share a recent common ancestor with him. As I worked on my family and client projects, I also noticed that recent Irish (especially Catholic who may be more native Irish) ancestors had a lot of matches and that many did not seem to connect with recent ancestors. I began to see that endogamy was on a spectrum. Some communities have accumulated more IBS segments than others.

How excited do I get about this 20 cM segment?

Most 20 cM segments we share with a match will be IBD (identical by descent or one we each received from a recent common ancestor), but about 25% of the time our 20 cM segment will be IBS (identical by state or one we received from a quite distant common ancestor). Though matches that share a 20 cM segment with you should (about 75% of the time) have a recent common ancestor with you, endogamy will increase the chances you do not share a recent ancestor. Endogamy will make IBS segments more common than 25%. If I was going to boil down managing endogamy to one question it would be: how excited do I get about this 20 cM segment? My answer is that the less endogamous your ancestor’s community is, the more excited I am about the 20 cM segment. 

In part these posts on endogamy arise from noticing the differences in my parent’s DNA tests. My parents each have 1 colonial and 7 mid-19th century immigrant great grandparents. Even though they each have the same number of somewhat recent immigrant ancestors, my mom (with 5 Irish great grandparents, 2 Dutch) has twice the matches (above 20 cM) my dad (7 German great grandparents) has at Ancestry.com: today it’s 714 to 332. The level of DNA test saturation in a community (probably higher for Irish people than German) will affect how many matches you have, but most likely the level of endogamy also plays a part. 

Why might the Irish be more endogamous than Germans?

Many communities with known endogamy have been geographically isolated, such as Puerto Ricans or Pacific Islanders. Even though diverse groups have contributed to its gene pool (native Irish, Vikings, Scots, Normans, English, etc), Ireland is an island, so some higher level of endogamy might be expected than a more centrally located place such as central Europe. One sign of endogamy in Ireland might be a higher rate of recessive traits: such as red hair (Mapping redheads: which country has the most?), and a high rate of rare diseases ( Could Ireland hold the genetic codes to crack serious diseases? Diseases, genes and Irish population history, Rare Diseases in Ireland).

Does endogamy make it easier for the DNA testing companies to identify ethnicity?

DNA companies have had an easier time identifying some ethnicities than others. One way to see this is when the DNA companies test their effectiveness with identifying ethnicities by plugging their reference population (all 4 grandparents from one locality) back into their algorithm. Some ethnicities will come back with less noise. 

 

The following graph comes from Ancestry.com’s most recent 2022 white paper on ethnicity:

Does ethnicity connect to endogamy?

In the last blog post I said that I thought the endogamy in my family went like this: German <  Irish < Ashkenazi Jewish. In Ancestry.com’s “Ethnicity Estimate 2022 White Paper” figure 4.1 above, I drew the horizontal lines under these ethnicities: Ireland, Germanic Europe, and Jewish Peoples of Europe. Essentially the fewer and more solid in color the square(s) for an ethnicity, the more often a person in that reference population (“single-origin individual”) will be assigned by the algorithm to the community that they came from. 

Germanic Europe has considerable “noise:” Germanic Europe’s reference population gets assigned to other ethnicities more than most. This is not surprising given the history and geography of German lands being the crossroads of many different populations. In contrast, Ireland and the Jewish Peoples of Europe ethnicities have less noise. Ancestry.com’s algorithm works better on them. Why? Probably because of endogamy. If endogamous populations have fewer distant ancestors, perhaps they have fewer different segments, and fewer segments can be more easily identified.  

A screenshot from Ancestry.com’s 2020 white paper can be seen below. Again Ancestry.com’s algorithm correctly assigned Ashkenazi Jewish and the Ireland reference populations nearly 100% of the time.

What evidence do we have for endogamy being on a spectrum?

In my experience, I have hypothesized that the probable levels of endogamy in my family look like this : Ashkenazi Jewish > Irish > German. One of my hypotheses when I look at my parents’ results is that more endogamous groups are easier for the DNA companies to assign to a correct ethnicity. Within my family and my clients, I have noticed a trend: those with recent (great or 2nd great grandparents) Irish Catholic ancestors get assigned to specific Irish communities at AncestryDNA.com. 

I have only had two cases with Protestant Irish great or 2nd great grandparents, so this is my theory for now. Neither of the two Protestant Irish cases had specific Irish communities at Ancestry.com (e.g. Munster), while every Irish Catholic case, 10 in all, has been assigned to a specific Irish community. It’s probable that Irish Catholics are more likely to have more native Irish ancestry than Irish Protestants- generally. More native Irish people have more ancestors with long histories on the island, which may have caused more IBS segments to accumulate in their community.

In contrast the more German communities in my family seem harder to identify correctly. My dad’s, aunt’s, and my ethnicity results have varied significantly over each update at Ancestry.com, mostly due to how the “German” parts are calculated. The relative ease of Ancestry.com to identify my family’s more endogamous ethnicities (Ashkenazi Jewish and Irish) over the less endogamous ones (German lands), may indicate that ethnicity can be some measure of endogamy. That plus the accumulation of recessive genes (e.g. rare diseases), and the mere fact that Ireland is an island are three reasons to suspect the Irish may be prone to many matches with a 20 cM segment and no recent common ancestor.

In the last post I showed the largest clusters from my dad’s MyHeritage.com matches. His endogamous Ashkenazi Jewish community, representing about 6% of his DNA, dominated his clusters. Would I see this with my mom’s Irish side? 

 

Like my dad, my mom’s brother here has a large cluster (red) of chromosome 9 pile-up matches. Besides that, my uncle has a few clusters that represent matches who share a variety of segments with my uncle and each other- clusters I want to take seriously (orange, turquoise, blue, maybe brown). But there are many clusters, with the telltale gray boxes, that are all one segment of chromosome 6- a likely IBS segment many people likely have from Co. Cork. My guess is that this segment is one reason Ancestry.com can peg my family as having a recent ancestor from Munster with their ethnicity results. I would say that this pile-up on chromosome 6 may be a result of endogamy.

 

The above DNAPainter.com screenshot of the middle of ch. 6  I got by first painting my uncle’s 2C (32.8 Mbp to 93.7 Mbp) on his grandma’s side, whose parent’s origins were in Co. Cork. I then painted those matches with the longest segment on the same on ch. 6. I found this mostly by researching the family trees of matches with long segments on MyHeritage.com. I found those with long segments by using the “Filters” tool, then “Sort By,” and then “Largest Segment.” I began to notice that many matches with long segments triangulated over the same place on ch. 6. The more matches piled up on the same segment, the more I became skeptical that all these matches shared a recent common ancestor with my uncle, but instead that this segment on ch. 6 might be a pile-up region (IBS) that many people with ancestors from Cork might share.

My strategy

Like my dad’s Ashkenazi Jewish line, I need to take note of pile-up regions, known (chromosome 9) and unknown (chromosome 6) in my uncle’s example above and de-emphasize those. Though I may look into the matches that have very long segments in pile-ups (e.g. the top 5 in purple above, besides the 2C in fuschia), I will focus more on clusters that match my uncle and each other over multiple segments. I will pay attention to location, and surnames. 

I hope these two posts on endogamy have helped you think about how endogamy may affect your cluster report and match list. The bottom line is that though matches that share a 20 cM segment with you should (about 75% of the time) have a recent common ancestor with you, endogamy will increase the chances you do not share a recent ancestor. We need to be wary of pile-up regions known and unknown, start with matches that share (multiple) longer segments with us, and build their trees first.

Learn More

To learn more about using DNA evidence in your genealogy research, you may want to sign up for the Research Like a Pro with DNA independent study course. In this course, Diana Elder, AG, Nicole Dyer, and Robin Wirthlin take you step by step through organizing and analyzing your matches and applying DNA evidence to focused research questions.

Other Articles in this Series

Endogamy, Pedigree Collapse and Multiple relationships: What’s the Difference and Why does it matter? by Diana Elder, AG
How Multiple Relationships Affect DNA Match Analysis by Nicole Elder Dyer
Multiple Relationships in an African-American Case Study by Allison Kotter
The Effect of Pedigree Collapse on DNA Matching: A Case Study by Nicole Elder Dyer
Visualizing Complicated Relationships: Working with Pedigree Collapse, Multiple Relationships, and Endogamy by Steve Little
Strategies for Overcoming Endogamy by Nicole Elder Dyer
The Irish: Endogam-ish by Heidi Mathis
Endogamy: Ashkenazi Jewish Case by Heidi Mathis

Sources

1. Southard, Diahan. “Your DNA questions answered live with Diahan,” Legacy Family Tree Webinars, 18 Sep 2020 (https://familytreewebinars.com/webinar/your-dna-questions-answered-live-with-diahan-3/: accessed 25 Jan 2021): Irish IBS comments in the “Segment Data” part of webinar, about minute 4. ” A lot of times people who are from Ireland will have this kind of baseline amount of DNA that doesn’t really mean they share a recent common ancestor. It just means they’re all from Ireland.”
2. Chalabi, Mona, “Mapping redheads: which country has the most?,” TheGuardian.com, 25 Nov 2013 (https://www.theguardian.com/politics/2013/nov/25/mapping-redheads-which-country-has-the-most; accessed 21 Oct 2022).
3. Stories.Abbvie.com, “Could Ireland hold the genetic codes to crack serious diseases?,” 15 Mar 2017 (https://stories.abbvie.com/stories/could-ireland-hold-genetic-codes-to-crack-serious-diseases.htm: accessed 21 Oct 2022).
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5. SaoirseFoundation.org, “Rare Diseases in Ireland,“ (https://www.saoirsefoundation.com/rare-diseases-in-ireland/: accessed 21 Oct 2022).
6. Adrion, Jeffrey et. al,, “Ethnicity Estimate 2022 White Paper,” AncestryDNA.com, (https://www.ancestrycdn.com/support/us/2022/08/ethnicity2022whitepaper.pdf : accessed 21 Oct 2022).,
7. Ball, Catherine A., et. al., “Ethnicity Estimate 2020 White Paper,” AncestryDNA.com, (https://www.ancestrycdn.com/dna/static/pdf/whitepapers/Ethnicity2020_white%20paper.pdf : accessed 21 Oct 2022).
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