Updated on: October 2, 2020

Endogamy is the practice of marrying within one specific group. It is usually an ethnic group, but it can also be a social group or caste. It’s a common practice and is not the same as incest. However, it does increase the risk of genetic disorders within a group. Endogamy is legal and is practiced by many religious and ethnic groups. 

Why Do People Practice Endogamy?

Endogamy can be intentional or it can occur by accident. Some communities want people to marry within their same religious group. Others intermarried based on cultural practices. It can be a combination of both of these things. 

In other cases, there isn’t much choice. People who live in isolated communities and don’t have access to travel don’t have much chance of meeting anyone that would enable them to not practice endogamy. This was the case in the past more than it is now, but these isolated communities still exist.

Sometimes incidences of endogamy occur “just because.” Let’s say your mother and her sister grew up in a house across the street from your father and his brother. Everyone spent a lot of time together and got along. There might have been no restrictions or cultural traditions and by chance, your family created an endogamous relationship when you and your cousin were born.

How Does Endogamy Affect Genetic Matching and Ancestral Research?

Endogamy can make genealogical research easier or more complicated, depending on the specific circumstances. People without endogamous relationships have to find eight sets of great grandparents, whereas people who have endogamy in their families must locate fewer. The same couple will appear on multiple lines in their genealogy results. 

Additionally, it’s easier to trace people when relationships were more insular.

Let’s say your family was Acadian Catholic and you want to know more about your heritage. It’s easier to research because if you know you descend from a group of people who are inclined to practice endogamy and they attended a church in a certain area, chances are church records will be enough to help you identify your entire family. The church kept detailed records of all marriages and required non-Catholics to be baptized before marrying. You’ll have access to a lot of information that is already organized and easily located from one resource.

It’s a different story, though, if your ancestors practiced a religion that did not keep such detailed records or that had its records destroyed. In these cases, endogamy makes your research more complicated. 

Communities that most often practiced endogamy include Ashkenazi Jews, Native Americans, Acadians, Amish, and Mennonites.

Without detailed record-keeping, it’s difficult to make distinctions with so much overlapping DNA. For example, let’s say your aunt on your mother’s side married your uncle on your father’s side. This creates a “double cousin” scenario. Not only do you share DNA with your cousin because her mother is your mother’s sister, but you also share DNA on your father’s side because her father is your father’s brother. You are maternal and paternal first cousins, which means you share twice the amount of DNA shared by first cousins.

Here’s where it gets tricky:

In standard DNA test, the company to which you submit your sample does not know that your family practiced endogamy. A double first cousin would look like a half-sibling on paper because she has approximately the same amount of DNA that you’d share with the same mother or father. It’s even more complicated when this relationship was further back in your family tree and happened with your grandparents or great grandparents.

And because endogamy rarely only occurred once in a family, most people end up sharing a lot more DNA with their cousins than you’d expect. It’s difficult to determine genealogical relationships because of DNA overlaps in your community, not because of one recent common ancestor, but because you share multiple distant relatives in common.

What Does an Endogamous Relationship Look Like When Conducting Genealogical Research?

It depends.

You’re not going to get any obvious signs or triggers telling you that endogamy occurred on DNA test results. 

One of the best ways to spot an endogamous relationship is to notice the total amount of DNA you share AND the size of the DNA shared. Most DNA testing companies provide this information. You’ll be examining the total DNA shared, the number of segments shared, and the length of the largest segment.

If this seems complicated, your best bet is to take your DNA test results to an expert analyst who can help you make sense of what you are looking at. They’ll assess your genetics and then you can take that information and apply it to your genealogy. They also offer services where they can help you analyze the genetics on your own.

It’s also important to consider geography. Where you live and the areas where you know your ancestors lived rule out some groups.

Joel is a writer with a passion for the science of DNA and the power of its manipulation.
Resources

“Endogamy - Sociology of Family - IResearchNet.” Sociology, sociology.iresearchnet.com/sociology-of-family/endogamy/. Accessed 30 Sept. 2020.

Pickholtz, Israel. “JGSI Jewish Genealogical Society of Illinois - ‘Jewish Genetic Genealogy - A Study in Endogamy’ by Israel Pickholtz.” Jgsi.Org, jgsi.org/event-2090195.

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