Do you want to if you have endogamy in your DNA matches? In this post, learn how to spot it, as well as see examples of endogamy so you can know what to look for in your DNA match list.
In this article, you’ll learn:
- A basic definition of endogamy
- How engodamy affects our DNA match list
- Signs that you might have endogamy in your DNA match list
- How to adjust for endogamy in your DNA match list – key for figuring out how you might be related to your endogamous DNA matches
There are several ways that people begin to suspect they might have found evidence of endogamy in their DNA match list. Maybe the shared matches or matches in common seem to overlap multiple lines of the family tree.
Alternatively, we might wonder why we share so many small DNA segments with relatively distant cousins.
If you have spotted these signs, you are correct in thinking about endogamy. Keep reading to learn more about this very interesting topic.
What is endogamy?
The “official” definition of endogamy describes it as the custom of marrying within the same ethnic, social group, or even social class. Many times, endogamy also includes the custom of discouraging marriage to outsiders not a member of the group.
This means that when people are searching for partners or mates within their social or ethnic group, it is likely that their choices for mates share common ancestors with them. After many generations of this practice, it would be difficult to find someone within the group who was not related to you in some way.
Sometimes, endogamy occurs by chance, and not necessarily by choice. Specifically, I’m referring to genetically isolated groups that don’t have regular contact with people from other areas.
For example, imagine a group of 100 people who left their original homeland to live on a large island. For our particular example, no one from the outside world has access to the island.
These 100 unrelated people, some men and some women, make their homes on this island and start families. The first few generations of descendants from the original founding group will likely not have endogamy, since the founders were unrelated to each other.
However, since the descendants can only choose mates from other descendants of the original group of founders, eventually they will have to choose someone that they are related to in some way.
It would be easy to imagine that, especially after the passing of many generations, almost all of the youngest generation of children would be related to each other in more than one way.
After many generations, descendants are unlikely to know all of the different ways that they are related to other members of their community.
In other words, there will be many ancestors shared on multiple lines of the family and most people will not be able to identify all of these individuals. They are most likely to know the most recent common ancestor, but not all of the common ancestors.
Here’s another example: A few lines of my grandmother’s family tree can be traced to Colonial American times. Both of her parents have roots in North America going back as far as the 1600s.
Eventually, we can find evidence that my grandmother’s parents likely shared multiple distant ancestors. Their descendants are unaware of this fact.
How engodamy affects our DNA match list
Endogamy can cause distant cousins to share more DNA with each other than is typical among cousins of a particular relationship distance. How does this work?
So, you know those kids on the island that I mentioned? Since they are all related to each other in many ways, they would also likely be DNA matches to each other.
If we gave all of those kids a DNA test, they would all show up on each other’s DNA match list.
This might be what you would expect.
Imagine two young residents of this island. They are friends, and they are discussing their families, and after a few minutes, they realize that they share a great-great-great grandmother.
I know it’s not super likely that a couple of kids know so much about their family tree, but work with me!
This means that they are fourth cousins.
Fourth cousins who share DNA typically might share as much as 75 centimorgans. These two fourth cousins that I mentioned above might share some DNA that they both inherited from their mutual great-great-great grandmother.
So far, so good – right?
Descendants of endogamous populations are often related to each other in multiple ways
What these two fourth cousins might not know is that they also share a great-great-great grandmother, a set of great-great-great-great grandparents, and even a set of great-great-great-great-great grandparents, all on different lines of their family trees.
Even more interestingly, these fourth cousins might even share additional common ancestors further back – from even before those 100 peoples decided to settle that isolated island. They came from a founding population with similar ancestral roots, so it’s quite conceivable.
In other words, these are fourth cousins, but they are also fourth cousins in a different line, fifth cousins, and sixth cousins. Plus, if they are related more distantly (further back than the initial population of that island), they might be eighth cousins, too!
People who are related in more than one way might share more DNA than is typical for their relationship distance
If these two “fourth cousins” took DNA tests, it’s possible for them to share DNA that they inherited from all six of their recent common ancestors. And if they did share DNA inherited from all, or some, of those ancestors, there is a good chance that they would share more DNA than 75 centimorgans.
If the DNA test detects substantial DNA inherited from the more recent shared ancestors, and smaller amounts of shared DNA from those distant ancestors, these two friends might show up as second-third cousins.
Signs that you might have endogamy in your DNA match list
When people with significant endogamy in their family tree look at their DNA match list, they might become confused and frustrated. Their top matches share 100-300 centimorgans with them, which would imply that their most recent common shared ancestors with those matches should only be back a few generations in their family tree.
For example, take a peek at the image below. It’s a screenshot of my husband’s DNA match list on Family Tree DNA.
I like the Family Tree DNA match list because it’s easy to sort and filter the matches, and information like segment size and total shared DNA is easily visible right from this list:
All of the people on this DNA match list share between 184-312 cMs with my husband. In the spirit of full disclosure, I will admit that I was very excited when I first saw this list. Six matches that share more than 184 cMs!
Based on all of the popular DNA charts out there, it is easy to imagine that my husband might share great-great grandparents (at the furthest!) with all of these individuals.
Spoiler alert: None of these individuals, except for the top match, are related to my husband in the past 8+ generations.
Alas, I still had to learn about endogamy.
You might have endogamy in your DNA match list if:
- You have lots of close matches but can’t find the connection anywhere
- You are descended from a population that has known endogamy (i.e. genetically isolated populations)
- You share lots of small segments with your matches
- You share a lot of DNA with your matches, but the size of the longest segment is small (more on this below)
It’s possible to spot endogamy even on a excellent site like Ancestry DNA (where detailed segment data not available). Take a look at the screenshot from my husband’s DNA match list below:
You can see that he shares 107 centimorgans across 11 segments with his top match. While I don’t know exactly how big those 11 segments are, I can assume that 11 segments divided into 107 centimorgans will lead to most of those segments being pretty small.
This is unlikely to be a true 3rd-4th cousin match with my husband. Possible, but unlikely.
How to adjust for endogamy in your DNA match list
If you are pretty sure that you are seeing the results of endogamy in your DNA match list, there is one thing that you can focus on to help you get the most from your DNA matches:
- Size of the largest shared DNA segment
As generations pass, the DNA segments that we inherit from our ancestors get smaller and smaller. This also means that larger shared DNA segments with our matches generally indicate a more recent shared ancestor.
There are no hard and fast rules when it comes to the size of DNA segments, but you can use the size of the largest segment to estimate how far back your most recent common ancestor might be.
For example, if the largest segment is 12 cMs in length, it could be from an ancestor as far back as 8 generations (or much further!). If you have a largest segment of 41 cMs, it is very unlikely that the most recent common ancestor is much further back than a great-great grandparent.
It should also be noted that it is possible for some of the smaller shared segments to be inherited from a different ancestor than the one that passed down the largest segment.
I hope that this post helped you learn a little bit more about your DNA match list, especially if you have lots of endogamy in your family tree. If you have any questions about something that you read here, I would love to hear from you in the discussion below.
Thanks for stopping by today!
Wednesday 16th of November 2022
I have a DNA match who was predicted to be 2nd-4th cousin, but when I got her in my tree, she was actually my 6th cousin. That’s because my 3rd great grandparents from those lines are first cousins. I enjoyed this article because it solidified my knowledge. Before I read it, I chalked up the discrepancy to “ranges” or “estimates” that we all hear about, but in this case, I can see that the large amount of DNA that we share has a more literal concrete basis. The source of this endogamy: West Virginia. I was tickled to learn of this because most of my endogamy traces to New England. In fact, Ancestry told me that I have tiny amounts of DNA in me from three ancestors born in the 1600s who are from Connecticut and Massachusetts. So I am glad for some diversity even if it’s more endogamy!
Friday 29th of July 2022
My question is how is it possible for a nephew to share more dna with his uncles 1st cousin than the uncle? Nephew shares 1338cm and the uncle only shares 635cm with uncles 1st cousin
Sunday 1st of May 2022
If Endogamy can inflate the numbers of shared dna. It would or could effect the value of the longest segment, right? Thus making use of longest segment under that circumstance unreliable in figuring out how close a relation actually is or am painstakingly wrong?
Monday 7th of March 2022
Intriguing!! A most thought provoking blog. This is undoubtedly an anomalous case. This many outliers is surreal. Are we sure that the last five matches are not missing a decimal in the third position or that the number of cM is actually number of segments? Also how recent is this test? I am guessing that this blog was originally posted on or before Feb 16, 2020. FTDNA updated on june 16, 2021. If tested before this date did the results remain the same??
Also have we considered IBS?? On Ancestry three of my matches and I do not have any matches in common. These are 9, 11 and 14 shared cM's. I write them off as either false matches or IBS. The longest block in the example is 7 cM, below the 9cM number. Have we checked for matches in common? It would be interesting to see these matches compared on the chromosome browser.
There are no hard and fast rules when it comes to the size of DNA segments,
No, but there hard and fast rules to simple math. Using just one of the outliers, if there are 184 shared cM and the longest segment is 5 cM then there would of necessity be at least 37 segments shared. 36 segments of 5 cM (highly unlikely that this many segments would be equal) and 1 of 4 cM. Much more likely that there would many more segments of shorter length. You have not shared with us the total number of segments.
I have tested on ftDNA, Myheritage and Ancestry. My closest matches on ftDNA (there are only four 132 or more) share 311 (14 segments-40 longest), 162 (7-70), 150 (11-30), 132 (8-39). Your screenshot must come from the autosomal match page. The chromosome browser page shows total number of segments.
And yes I descend from an endo-gamous society: Western NC, Tenn and Ga. Some of my matches per Ancestrydna have as many 6 different connections over a period of 8 generations. Yet I have found no outliers to this extreme. 5th great grandfathers without the endo-gamy would give us at least 128 possible connections.
Thursday 17th of March 2022
Hi Gera, You ask a lot of excellent questions. I am probably going to update the post, but I can say that the basics have not changed much. However, I can see a benefit in providing further information from the chromosome browser for each match and more recent screenshots. Thank you for providing this thought-provoking comment!! Sincerely, Mercedes
Monday 7th of March 2022
My parents were first cousins 1x removed which means that in the family that I have most DNA links with, my mother and I are in the same generation which causes complications with thinking through how people relate. I've had to draw a chart to keep thinking clearly. It also means that getting a parent to take a DNA test has meant that Mum and I come up as the same relationship to lots of matches so isn't the step farther back that you hope to get from a parent. Your articles are some of the most intersesting I've found. Thanks