What endogamous communities existed in the past? What DNA fingerprint did they leave behind? Jayne reviews studies about various historical communities affected by endogamy. Were your ancestors part of this history?

What has been written about your ancestors’ endogamous communities? If you have been able to identify them, perhaps you’ve already read up on them. History books and articles can help you better understand and connect with your intergenerational identity, even if it takes you a long time to sort out exact individuals on your family tree. 

Looking specifically through the lens of endogamy, you may find fascinating genetic, historical or sociological studies that help your overall understanding of your ancestors’ experiences. Just as a reminder, endogamy is when a community marries within its defined culture or location for many, many generations. In genetic genealogy, we look at the genetic effects of prolonged endogamy.

Not all endogamous communities were the same. Some were deliberately fostered for religious or socioeconomic reasons; others resulted by circumstance. Some communities have practiced endogamy for millennia, others have adopted the practice only briefly. Geography, war, racism, and other factors may have shaped your ancestral community’s experience. DNA studies have even begun to better define and refine some of these communities.

Even studies about groups that don’t reflect your heritage can help you understand the impact of endogamy, and the decline of its practice in certain groups. These articles explore some of the special cases of endogamy: prolonged cultural/religious intermarriage, nested endogamy, endogamy over a more limited number of generations, and isolation by geography. They suggest some of the genetic effects that might be expected in descendants from populations with similar characteristics. So dive into these primary research articles to learn more about what you might expect to see in your DNA results if endogamy is part of your historical landscape.

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Historical endogamous communities

Prolonged cultural and religious intermarriage, plus nested endogamy

Jewish endogamous communities in North Africa

DNA works! The genetic findings from this 2012 study (Campbell) of Jewish populations in North Africa support the historical knowledge of how this endogamous group formed over 2,000 years ago and how it’s changed over time. A thorough genome-wide analysis was performed on over 500 people from 5 contemporary North African Jewish groups (Moroccan, Algerian, Libyan, Tunisian, Djerbian). 

North Africa regions map. Peter Fitzgerald, Wikimedia Commons. CC BY-SA 3.0

Researchers carried out a series of comparisons of their genetic data to determine their relatedness to themselves and other surrounding groups: the North African Jewish groups (1) compared among themselves, (2) compared to immediate geographic neighbors that aren’t Jewish, and (3) compared to historical populations of origin or others that they may have mixed with. Genetically, among the North African Jewish people themselves two distinctive Morocco/Algeria and Libya/Djerba subgroups presented. They showed genetic separateness even from each other, suggesting an extended practice of disconnection from not just the larger world but even from other Jewish regional neighbors. When compared to people from broad Eurasian populations, they showed the most genetic affinity for other Ashkenazi and Sephardi groups, but were quite genetically incongruous with regional neighbors in North Africa that had no Jewish heritage. 

These findings illustrate a theme that you could find evidence of in your own inter-related lineages: nested endogamy. The worldwide Jewish population is broadly endogamous and has intermarried for millennia, but this is a huge group that has further smaller subgroups that are additionally endogamous inside the larger umbrella population.

It should be noted that MyHeritage reports five major Jewish regions, more than any other company, as well as many, many others in their Genetic Groups. (The five are Ashkenazi Jewish; Sephardic Jewish – North African; Ethiopian Jewish; Yemenite Jewish and Mizrahi Jewish – Iranian/Iraqi. If your ancestry may include these groups and you haven’t tested there, you may want to transfer your DNA to MyHeritage and pay the $29 unlock fee to see whether they identify your DNA with these groups.)

Endogamy Over a More Limited Number of Generations

Endogamy in German Lutherans in Kansas, and Splinter Groups in Rural Illinois

In her 2021 book (Coburn), Carol Coburn details some of the religious and social factors that preserved an insular existence for German Lutherans in Kansas in the late 19th century. Ethnic and religious practices were intentionally cultivated to keep the community from integrating with broader American society. The German language was used in worship services and in schools, and group members faced exile from their community if they associated with “outsiders.” Leaders of this tradition saw threat and hostility to their way of life everywhere and communicated this to their adherents. 

For several decades this community posture kept their rural congregations insulated from neighbors outside of their tradition. With developments in transportation, communication, and an emerging urban economy, subsequent generations began to have dealings outside of the core community. Critically, World War I ushered in an era that made total isolation a dangerous stance for the Synod and its congregations. Residents of this German-Lutheran community began to gradually expand their networks past exclusively ethnic or religious associations by allowing members entrance to the outside world after careful indoctrination and deep forging of family bonds. 

Descendants of this group today are 2-3 generations removed from the formerly isolationist existence of their community, but it is possible that the genetic evidence of endogamy may be detectable. While not often recognized as “classic endogamous populations,” pockets of insular groups like this one in the United States throughout the 18th- and 19th-century may be relevant to your family’s DNA story. 

This more time-limited endogamous dynamic may be something that many families worldwide might encounter. A recent DNA study (Owings, et al.) detailed here examined the genetic effects of a few generations of endogamous isolation of splinter groups in the countryside in Illinois. Even with almost 1 million DNA markers tested, researchers did not see a detectable genetic signature that allowed the briefly isolated groups to be distinguished from one another genetically. Affinity of the groups to deeper source populations (Britain and more broadly European) was apparent in their DNA. Despite a few generations of practicing endogamy, the predominant genetic signal of these isolated Illinois groups connected them more to their deeper European origins rather than showing sharp distinctions from each other.

Periods of isolation and endogamous marriage may leave a lasting imprint on the genetic signatures of descendants, but in some groups this may not be as readily detected as in others. There are several factors that may influence this, including the genetic distinctiveness of the founders of new endogamous groups, the length of time over which endogamy is practiced, the degrees of intermarriage participated in, and other dynamics. And likely no endogamous group has the same set of influential factors, so this should be considered on a case-by-case basis.

An example of one of these case-specific factors employs detailed 1981 census data, Brigham Young University researcher Tim Heaton (Heaton) found a strong connection between religious affiliation and the practice of marriage within a faith tradition. Social factors shown to support endogamy were common concepts of roles, norms and networks shared by couples. Conversely even with high levels of cohesiveness, group size had the effect of lowering the prevalence of endogamy. So a smaller, insular group was more likely to have high levels of endogamy overall than a larger general tradition with many more members. 

Do you expect endogamy in your family may have occurred over a more limited number of generations? Do you see any of these social trends or other influences reflected in your ancestors’ communities? How do you suspect these might affect the level of genetic distinctiveness you might expect to see today in their descendants?

Isolation By Geography Results In the Prolonged Practice of Endogamy

Endogamy on Easter Island

In this study (Hernández, et al.) of surname diversity from 2000, researchers evaluated changes in the practice of endogamy on Easter Island, the most geographically isolated-by-distance population in the world. The island was colonized in the 5th century by a Polynesian expedition, and remained completely isolated until 1722 when Dutch explorers made the initial contact that brought the Rapanui people of Easter Island back onto the world stage. 

Bottleneck effect. Wikimedia Commons. CC BY 4.0.

The population suffered a devastating population decline to just 110 people counted in 1877 due to exploitation and exposure to epidemics, a significant genetic event known as a population bottleneck. This causes the genetic diversity of subsequent generations to be reduced dramatically from what it would have been with a larger pool of ancestors. The result is a cohort of descendants that are quite genetically distinct from all other groups in the world.

With centuries of endogamy compounded by a significant genetic bottleneck, modern Rapanui descendants would be expected to carry an extremely distinguishing genetic fingerprint. Even once under the sovereignty of Chile in 1888, the Rapanui maintained a strong practice of endogamy through 1965. From 1937-1965, 96.5% of all Easter Island births were from endogamous marriages, with a sharp decline evident over 1966-1980 with 56.8% of births between Rapanui couples. The declining trend continued through 1996 when just 49.2% of births were attributed to unions from within the island. 

Even though descendants of the original Rapanui have continued to mix with others outside of Easter Island, the legacy of endogamy and genetic bottleneck would be expected to shine clearly through their genetic profile. Do you have any ancestors that may have been part of a genetic bottleneck event, or centuries of profound genetic isolation by geographic distance or otherwise?

The Declining Practice of Endogamy in Some Modern Groups

Exogamous Jews in Small-Town USA

Where endogamy is the practice of marrying within an ethnicity, religion, or other social structure, exogamy is inter-group marriage. In a 1969 publication (Schoenfeld), Eugen Schoenfeld highlighted the higher rate of Jewish exogamous marriage in small towns compared to urban areas. Within 16 small towns in Illinois, 39% of Jewish marriages were exogamous. 

Factors affecting the practice of endogamy include socioeconomic standing and strong cohesion in ethnic groups (language, custom, and national prejudices). In places where the socioeconomic standing of an ethnic group remained low, endogamy was more prevalent. In smaller towns where an endogamous group is the minority, adherents are less likely to find a marriage partner within their tradition. Do any of your ancestors come from a tradition of endogamy that may have ended due to lack of marriageable partners in their accessible circles (the small town effect or otherwise)?

Considering Endogamous Trends In Your DNA Match List

Many factors may influence the historical and continued practice of endogamy in your family’s history. Prolonged endogamy in particular leads to elevated DNA sharing among descendants of a much larger group that may not be very closely related in real time. You may be able to make an educated guess about how impactful endogamy might be in your DNA match list. 

Are you seeing many false “close” cousins based on shared DNA that is actually due to a centuries’ old tradition of endogamy? Are you seeing elevated sharing due to centuries of intermarriage motivated by geographic isolation? If endogamy was practiced in your family for a more limited time, do you suspect the levels of elevated DNA sharing may be more minor? Do you see a more recent trend of declining endogamy in your more recent generations, or is the practice still going strong? 

These and other questions may help you to contextualize your DNA match list and sort out how likely it is your list of cousins reflects recent shared ancestry, or if the DNA signals are connecting you to deep endogamous trends. 

Diahan helps you to sort all of this out and more in the popular and unique Endogamy and DNA Course. See what you can learn about your people!

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What to read next? Where’s Your Endogamy?

1. Campbell CL, Palamara PF, Dubrovsky M, Botigué LR, Fellous M, Atzmon G, Oddoux C, Pearlman A, Hao L, Henn BM, Burns E, Bustamante CD, Comas D, Friedman E, Pe’er I, Ostrer H. North African Jewish and non-Jewish populations form distinctive, orthogonal clusters. Proc Natl Acad Sci U S A. 2012 Aug 21;109(34):13865-70. doi: 10.1073/pnas.1204840109. Epub 2012 Aug 6. PMID: 22869716; PMCID: PMC3427049.
2. Coburn, Carol K. “The Outside World,” chapter 5 in Life at Four Corners: Religion, Gender, and Education in a German Lutheran Community (University Press of Kansas, 2021), pp. 112-135.
3. Owings AC, Fernandes SB, Olatoye MO, Fogleman AJ, Zahnd WE, Jenkins WD, Malhi RS, Lipka AE. Population Structure Analyses Provide Insight into the Source Populations Underlying Rural Isolated Communities in Illinois. Hum Biol. 2019 Feb 17;91(1):31-47. doi: 10.13110/humanbiology.91.1.05. PMID: 32073243.
4. Heaton, Tim B. “Religious Group Characteristics, Endogamy and Interfaith Marriage,” Sociological Analysis (Canadiana, Winter 1990, 51:4), pp. 363-376.
5. Hernández M, García-Moro C, Moral P, González-Martín A. Population evolution in 20th-century Easter Island: endogamy and admixture. Hum Biol. 2000 Apr;72(2):359-77. PMID: 10803666.
6. Schoenfeld, Eugen. “Intermarriage and the Small Town: The Jewish Case,” Journal of Marriage and Family (Feb 1969, 31:1), pp. 61-64.