As genealogists we want to understand our match lists. We want to identify the matches that will give us the solid clues we need to make progress on our target ancestor’s family tree. Endogamy and its close cousins, pedigree collapse and multiple relationships, complicates that. Diana laid out the definitions in the first blogpost in this series: “Endogamy, Pedigree Collapse, and Multiple Relationships: What’s the Difference and Why Does it Matter?” Nicole wrote about strategies for overcoming endogamy in this post: Strategies for Overcoming Endogamy.
Endogamy refers to when intermarriage has occurred over many generations (centuries) in a community, whereas pedigree collapse occurs in a much shorter time frame. At first I thought endogamy would be a non-issue for my own family research (mostly 19th century German & Irish immigrants), but then my dad turned out to have a small (3-6%) amount of Ashkenazi Jewish DNA and I learned that Ireland may be affected by low level endogamy too. How does having more marginal endogamy affect my research? Since my own family tree has ancestors of varying levels of endogamy (i.e. low for German, moderate for Irish, and high for Ashkenazi Jewish), I have needed to access these different levels to make progress. I hope to unpack in this post and the next one my own takeaway lesson from my experience: endogamy is on a spectrum.
The Human Family
In the largest sense all humans are endogamous. At some point in the distant past any human alive today will have a common ancestor with any other human (that point was about 1000 years ago between people of European descent and about 2100 BC between all people). Therefore when we say endogamous, it is a relative term (no pun intended). Some communities will be generally less endogamous than others. We are all human so we all share a lot of the same DNA with each other, but some communities will share slightly more within their community than average. In other words, endogamy is on a spectrum.
The higher the endogamy in your community the fewer distant ancestors you have. The fewer ancestors your community has, the more your community shares identical by state or IBS segments. IBS segments are those we and our match share from our common distant ancestor, as opposed to matches that we share IBD (identical by descent) segments that we each received from a common recent ancestor (up to 5-8 generations ago). Endogamous communities will have more IBS segments, which make more of our matches appear to be more closely related to us than they are.
Endogamy is on a spectrum
I have a range of probable endogamy from my ancestral lines: German < Irish < Ashkenazi Jewish (AJ). My AJ community likely has the highest endogamy here for several reasons, but one being a bottleneck about 1000 years ago. Why would Germans probably have the lowest endogamy of these groups? I wrote about this in “Tracing Your 19th-Century German Ancestors: DNA” (see Figure 2), but essentially people from central Europe have generally experienced greater population mixing than more geographically isolated communities. This means that the average German ancestor likely had more distant ancestors than the average Irish ancestor. In the next post I will write more about Irish “endogamy.”
Two factors complicating my family’s endogamy:
1. Incomplete family trees make it hard to know which matches a DNA tester shares a recent common ancestor with (IBD) and which do not (IBS). AJ have faced tremendous upheaval, took surnames later, and so can be hard to trace past the mid-19th century (my dad’s 3rd-4th great grandparents would have been born before that). Therefore finding where my family and an AJ match connect on paper may be especially difficult.
2. Germans tend to not take DNA tests, and so my dad’s 19th century non-endogamous German lines will have few matches to begin with. The fact that so far Germans as a group have a low rate of taking DNA tests means German endogamy will just be harder to run into.
In spite of the two caveats above, we can estimate that some communities will have more IBS segments than others. Does this mean Germans have no level of endogamy? No, people with a German ancestor from a small village will likely share IBS segments with others from the same village and will appear to be closer relatives than they are. Nevertheless, Germans with IBS segments from the same village will likely share these with fewer matches, because their IBS segments are less widespread in the descendants of people from German lands than people whose ancestors have more endogamy (fewer distant ancestors), such as the Amish.
Looking at my mostly German dad’s match list illustrates some of the main principles of how endogamy affects DNA analysis. My dad has a small but significant amount of Ashkenazi Jewish (AJ) DNA (3-6%) that stays consistent over many updates over several DNA testing companies. I hypothesize that one of his seven 19th century German immigrant great grandparents may have been about ¼ to ½ AJ. There is a big difference between how his non-endogamous (German) versus his more endogamous (AJ) ancestry shows up in his match list.
Endogamous vs. Non-endogamous communities at MyHeritage.com
My dad’s MyHeritage.com Autocluster chart illustrates what I mean. He has a lot of AJ matches relative to his matches from non-endogamous lines. I’ve hypothesized that my dad has about an AJ 3rd to 4th great grandparent, and if true, that ancestor from an endogamous community dominates his cluster chart below. Filtering for ethnicities at MyHeritage.com, I find that 20% of his matches have some AJ ethnicity, further indicating that his 6% AJ community claims a disproportionate number of my dad’s matches.
I will set aside the second cluster because it is over the known pile-up region on ch. 9 (38.3 Mbp- 72.6 Mbp) from his one colonial German (“Pennsylvania Dutch”) 2nd great grandma. After that I note that the large first cluster (red) plus several others (yellow, light blue, dark blue, brown) are AJ matches between 15-37 cM on the far end of ch. 16- a likely pile-up region (illustrated below). You can see the fairly large numbers of matches that are a part of more than one cluster (gray boxes) are associated with my dad’s AJ clusters- a common phenomenon with endogamy. The fact that my dad’s largest MyHeritage.com clusters are likely pile-up regions illustrates his situation (and the need to watch out for pile-up regions). His endogamous community is overrepresented. His non-endogamous German lines do not have more than a few matches generally (except the great-grandma from Baden in the last peach cluster) and so tend not to form clusters in spite of my dad having more of these ancestors.
The above DNAPainter screenshot of the right end of ch. 16 I got by first painting my dad’s ethnicities from 23&Me. To get the ethnicity CSV files from 23&Me: Start at the top of the 23&Me home page > “Ancestry & Traits” at the top > “Ancestry Composition” > “Scientific Details” > scroll down to the bottom of the page for the “Download Raw Data” button > copy & paste CSV files in the same way you would with a match’s data into DNAPainter. After that I painted my dad’s best matches from MyHeritage.com. I found my dad’s AJ matches by using the filtering tool at MyHeritage.com. On the “DNA Matches” page, I selected “Filters” > “Ethnicities” > “Ashkenazi Jewish,” then I selected “Sort By” > “Largest Segment.” This gave me a quick way to filter for my dad’s AJ matches, which I could next identify the best of these by the criteria listed in the next section.
What is the strategy for clearly endogamous populations such AJ?
- Notice pile-up regions. De-emphasize these pile-up matches, except perhaps those matches that share a long segment (at least 20-23 cM) that extends well beyond the pile-up area.
- Select matches you share the most DNA with combined with the longest segment. Several AJ DNA specialists recommend eliminating matches whose longest segment is below 23 cM, and not counting any segments in the total below 10 cM.
- Build family trees of these prioritized matches. Notice any common locations (birthplaces) first, then surnames.
I realize that it will be challenging to identify my dad’s mysterious AJ ancestor, because AJ mid-19th century records and older become especially difficult to find due to the community’s history of forced dislocation and late adoption of surnames. For several reasons not important to this topic, my theory now is that my dad’s great grandma from Bavaria may be partly AJ. Some of the better AJ matches (i.e. longer segments, non-pile-up segments) have ancestors from Bavaria. Other non-AJ matches on this great-grandma’s line also come from the same specific place in Bavaria. My next steps will be to find more records on this great grandma’s line in the U.S., and then hopefully in Europe. I will then start building some of these interesting matches’ trees more fully.
I hope my dad’s case has illustrated how endogamy can increase the number of matches, especially when the tester’s other ancestral lines are relatively non-endogamous. With my dad’s endogamous line, I need to be more careful about pile-up regions. Endogamy means it will be tricky to identify the matches that do share a recent common AJ ancestor with my dad, but it’s worth a try. In the next blog post, I hope to continue to illustrate how endogamy is on a spectrum with a community with likely moderate endogamy- the Irish.
To learn more about using DNA evidence in your genealogy research, you may also 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.
- FamilyLocket.com, “Endogamy, Pedigree Collapse, and Multiple Relationships: What’s the Difference and Why Does it Matter?,” 2 Sep 2022, Diana Elder (https://familylocket.com/endogamy-pedigree-collapse-and-multiple-relationships-whats-the-difference-and-why-does-it-matter/: accessed 21 Oct 2022).
- FamilyLocket.com, “Strategies for Overcoming Endogamy,” 5 January 2023, Nicole Dyer (https://familylocket.com/strategies-for-overcoming-endogamy/ : accessed 17 Jan 2023).
- YouTube.com, “How many unique ancestors do you have?,” 11 Aug 2014, Roots and Routes, (https://www.youtube.com/watch?v=tgXu19LNYEk : accessed 21 Oct 2022).
- Journals.plos.org, “The time and place of European admixture in Ashkenazi Jewish history,” 4 Apr 2017, James Xue, et. al.,(https://doi.org/10.1371/journal.pgen.1006644 : accessed 21 Oct 2022).
- Blog.Kitty Cooper.com, “More on Ashkenazi DNA,” 23 Mar 2021, Kitty Cooper, (https://blog.kittycooper.com/2021/03/more-on-ashkenazi-dna/ : accessed 21 Oct 2022).
- Woodbury, Paul. “Dealing with Endogamy,” Legacy Family Tree Webinars, 14 Oct 2020, (https://familytreewebinars.com/webinar/dealing-with-endogamy/ : accessed 18 Sep 2022).
- Ferretti, Alec. “Strategies for Analyzing Endogamous DNA, ” 12 Jun 2022, handout (https://www.jgsgb.org/event/ferretti-endogamous-dna/ : accessed 21 Oct 2022).
- Lara’s Jewnealogy, Diamond, Lara, “Ashkenazi Shared DNA Survey- September 2019 Update,” 1 Sep 2019, (https://larasgenealogy.blogspot.com/2019/09/ashkenazic-shared-dna-survey-september.html: accessed 21 Oct 2022).