The Endogamy Files: Visualizing Endogamy in Your Tree

The first post in this series described endogamy, the practice of mating within a relatively small group over many generations, such that many marriages occur between cousins, often distant ones.  The post prompted several readers to ask some version of “Does my tree qualify?”  That’s a great question, because it means readers are grappling with how cousin marriages might affect their own genealogical research.


Pedigree View

One way of assessing pedigree collapse and endogamy is to visualize it in your tree.  However, the typical formats we use for family trees—pedigrees and descendant charts—don’t display the information we need in a way that’s easy to interpret.

Here’s an example in which the ancestors who appear more than once are circled.  While we are accustomed to this pedigree perspective, without the added circles, the degree of endogamy would not be immediately apparent.  What’s more, a graphic of this type becomes increasingly large as we add generations, making it harder to take in all of the information at a glance.

Cajun pedigree as viewed at


Exploring Family Trees

My favorite tool for visualizing endogamy in a gedcom file is the Exploring Family Trees tool by Brad Lyon.  You can read more about how to use it here.

This graphic shows the same tree as above, but the endogamy is much more apparent.  The “swoops” trace ancestors who appear two or more times in the pedigree; the more swoops, the more endogamy.

What’s more, this view can show many more generations in a compact space.  The box marks roughly the seven generations in the pedigree above.  This allows us to see the extensive endogamy further back in the tree, in the 1600s and 1700s.  It’s a classic pattern of settlement, when a small population colonized land far from their previous homes and where marriage partners were limited.

The diagram even highlights non-endogamous (or perhaps less-endogamous) lineages that married into the population.  These lineages appear as largely vertical branches.  In this particular tree, they include French, Irish, and Spanish settlers who married Louisiana’s Acadians in the 1800s.


Tally Your Duplicate Ancestors

How many of your ancestors appear more than once in your tree?  And how many times do they show up?  An easy way to find this out is with the Tree Completeness and Pedigree Collapse reports for trees at DNA Painter.  (Basic trees are free, but you’ll need a subscription if your tree goes deeper than 4th great grandparents.)

The link to tree completeness is at the top right of your tree.  As you can see, mine has 255 people who appear more than once.  The Pedigree Collapse report names them and tallies how many times each individual appears in the tree.

How Much Endogamy Is a Lot?

Even the tools described here, though, don’t quantify the endogamy.  Is it a little?  A lot?  Somewhere in between?  As we’ll see in a subsequent post, I consider the example above to be moderate endogamy.

That assessment is based on DNA matches, though, not a tree.  Ironically, dog breeders have tools that can calculate the amount of pedigree collapse, but we don’t have convenient tools to do the same thing from our gedcoms.  (Developers:  Hint!  Hint!)


Learn More!

Endogamy is the last frontier in genetic genealogy.  Learn best practices for working with this common challenge in this upcoming educational opportunity.  This class will help you understand what endogamy is, why it complicates DNA analyses, how to gauge it, and some strategies to work most effectively with your DNA results.

You will have opportunities to ask questions during and after the talk.  Attendance is limited to 35 participants per session, with two sessions of the same material currently scheduled to accommodate various schedules (5 PM PDT on 12 April and 10 AM PDT on 13 April).  Registered participants will have access to the recording for 2 weeks.  Captioning available, and a handout is included.

Follow me on Eventbrite to learn about upcoming events!


Other Posts in This Series


11 thoughts on “The Endogamy Files: Visualizing Endogamy in Your Tree”

  1. Hi Leah – thanks for this post, but I find the 2nd graph to be completely unintelligible! What on earth is a “swoop’? Where is it in the graph? Why are blue dots seeming to go up the right hand usually female side – do they represent males and pink dots females but are reversed from the usual format? I think we need some labels for the points you’re making! And how is “endogamy much more apparent”? It is? Where? It just looks like a snarled mess that can’t be followed. The first chart is fine and quite understandable, but the second is a snarl. Please explain!

      1. Thanks Leah – these two articles did the trick. Much more understandable now. So the “swoop” is the horizontal line that crosses many branches to hook up with another branch even though it may not be the same generation? I do still wish there were a few labels and arrows on the swoop diagram, though. I’ll have to upload my own GEDCOM and use the tool to solidify my understanding, I think.

        1. The live tool has pop-ups with names/dates and will highlight the multiple lines of descent from a given ancestor. It’s hard to show everything it can do in a static image. I encourage you to try it!

  2. Has anyone published a % of endogamy expected in one’s tree? Jim B published this week an expected 2% NPEs so wondered about endogamy’s percentage expected.

    I do not find any endogamy in my tree and it is robust. Thank you for this article.

    1. The only public data I know of along those lines are in the supplemental materials to a paper published by 23andMe scientists in 2012. They compiled data on the average amount of DNA shared between “unrelated” members of more than 100 different populations.

  3. I started my DNA research with Ancestry many years ago. I could not figure it out because I was new to the field and new to DNA research. I finally color coded my father’s line blue and my mother’s line red. For the first time I understood my tree. I am a descendent of colonial ancestors who intermarried a lot. I even have a female ancestor who married her uncle and her nephew. The CM share of cousins at the same level is way out of proportion which is always the hint to move up the line for a cousin marriage. I don’t have a tree I have a tangled ball, and a lot of autoimmune disorders in my family. My tree has been incredible helpful to doctors as a map for diagnosis for disease in my family.

  4. Great series of posts.
    I have one marriage of 4th cousin ancestors someone else discovered decades ago. Since then, nothing in the direct ancestral line. But I do have matches with people who have the same couple appearing repeatedly in lines in their tree, so it makes it hard to work out how far back our CA couple really is.
    The other major problem I have with endogamy is people marrying others within a restricted geographical area. In one area where records were available, a study of descendants of an ancestral couple from 1680 has helped show some points of multiple relationship to several matches. Another region has quite limited records and I can only make estimates of some DNA match connections in the late 1700s, because there has been no later connection found since despite chasing every possible line. (NPE surprises may perhaps be awaiting me – although adoptions/fostering of orphans was prevalent, so far all of the many examples discovered have retained their original name from birth, but there’s always a first exception to be found.)
    Its a challenge, so help like these posts are much appreciated.

  5. Thank You, My maternal line arrived in Philadelphia in mostly the late 1600’s and stayed in a three county area for close to 250 years, they were mostly Mennonite, some Amish and some dunkers and Schwenkfelders. My mother was one of the first to marry someone outside the group, aside from two other women on her paternal side who married non- Germans. I struggled for years tracing her family and found many cousin marriages, some double first cousin marriages. I plan on getting my DNA done and am wondering how all of this will effect the results.

  6. When you have common ancestors in your family tree, that shows up in your DNA as runs of homozygosity. You inherit half of your genes from your mother and father so if they share a common ancestor, that means there will be tracts in your genome where the each half is identical.

    These tracts are detected as runs of homozygosity and they can be used to compute a coefficient of inbreeding. That’s the probability of inheriting genes from a common ancestor on the maternal side and paternal side. For example, if your parents are first cousins, you would have a higher coefficient of inbreeding than if your parents were second or third cousins. You would also have a higher coefficient of inbreeding if you’re descended from an insular community or diaspora.

    Anyway, if you have your raw DNA file, you can check your coefficient of inbreeding at my company’s free app at

    1. Can you please point me to your company’s Terms of Service?

      It’s important not to confuse endogamy with consanguinity and also to recognize the limits of consanguinity. My parents are not related, but endogamy has a substantial impact on my DNA matches because my mother is from an endogamous population. Her parents were fourth cousins and she has a short run of homozygosity (8 cM), but her full brother has none.

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