Why Do Some People Marry Within the Same Group: This is Endogamy

Endogamy is the practice of marrying within the same group. It’s often practiced as a cultural custom, though it can also be dictated by law or happen by circumstance.

Some examples of endogamy include marrying within the family, clan, tribe, and caste—or the same social, cultural, religious, or ethnic group.

Old Order Amish, Orthodox Jews, Cajuns, Polynesians, French Canadians, the Parsi of India, the Yazidi, and Armenian-Iranians are endogamous societies.^1,2

The practice of endogamy is not the same as incest, which is considered illegal and defined as sexual relations between close blood relatives.³ However, endogamy—like incest—increases the risk of genetic disorders.

Why Do People Practice Endogamy?

Endogamy is a common practice in many cultures. It can be done as part of a custom (such as religious tradition), or it can be dictated by law.

The group can isolate and preserve itself by practicing marriage within a specific group. It is a form of segregation that prevents one group from merging with other groups that do not share the same culture, beliefs, practices, or resources.⁴

Some families engage in endogamy to retain their property, wealth, or social class.⁵

Endogamy also helps one’s social group survive by promoting unity and giving them better control over the resources they need to thrive.³ This is why endogamy is common in displaced populations—such as migrants and refugees—who live in places away from their geographic origin.

In other cases, people get into endogamy because they have little choice. A good example is living somewhere isolated, like an island (geographical isolation). Some other practices of endogamy are also innately racially motivated, as many conservative societies look down on and want to avoid interracial marriages.

Are There Different Types of Endogamy?

There are several types of endogamy, it depends on the social unit and if they’re practicing certain cultural traditions, religions, or how isolated they are. Here are a few of them:

• Cultural Group or Social Endogamy – Endogamous marriages within a cultural or social group are often done to preserve tradition and cultural identity
• Religious Endogamy – When people center their faith, they’re often expected by their religious community to marry only within that same faith community or have their potential marriage partner convert first
• Ethnic Endogamy – This is done to preserve cultural practices and ethnic homogeneity
• Caste Endogamy or Class Endogamy – In certain societies, a caste system is heavily enforced, and people only marry within their caste group to prevent caste intermixing
• Royal Endogamy – This was done to maintain the purity of bloodlines, which was important to aristocratic and royal families
• Geographic Endogamy – Many communities that practice endogamy usually have no other choice as they’re pretty isolated from other societies

What Are Some Endogamous Communities?

Some of the most well-known endogamous communities are:

• India’s caste system
• Coptic Christians
• Greek Cypriots
• The Amish
• The Church of Jesus Christ of Latter-day Saints
• The Yazidis
• The Alawites
• Ashkenazi Jews

Many other ethnic minorities also tend to practice endogamy to maintain traditions, practices, and even because they have little choice or social mobility.

Are Endogamous Communities At Risk for Genetic Diseases?

Yes. Since endogamy isolates one’s group, it results in a small gene pool. Endogamy increases the risk of genetic disease.⁴

The following conditions are commonly seen in endogamous communities: 

• Stillbirths and increased risk of abortions
• Perinatal mortality
• Congenital malformations
• Autosomal recessive disorders

The genetic diseases that affect endogamous groups tend to vary. For example, Bloom syndrome is a rare condition common in Ashkenazi Jews and other tight-knit Jewish communities.

When people from the same group marry, their children have a higher chance of inheriting harmful genetic traits from both parents. Some genetic disorders that can be passed on include:

• Cystic Fibrosis – A genetic disorder that affects the lungs, digestive system, and more. Thick mucus production can cause breathing and digestive problems.
• Sickle Cell Anemia – A blood disorder where red blood cells become deformed, causing pain, anemia, and organ damage. Sickle cell anemia can be more prevalent in groups that practice endogamy and have a history of malaria.
• Tay-Sachs Disease – A rare genetic disorder that affects the nervous system. It can lead to severe physical and mental disabilities, usually in infancy.
• Thalassemia – A group of blood disorders where the body doesn’t produce enough hemoglobin, leading to anemia and other health issues. Due to limited genetic diversity, it’s prominent in the Mediterranean, South Asia, and the Middle East.
• Hereditary Nervous System Disorders – Some groups may have a few genetic nervous system disorders, including Charcot-Marie-Tooth disease and hereditary ataxias.

Unfortunately, this increased risk for certain genetic disorders can lead to a group’s extinction. It’s tricky as there is rarely a hard boundary for endogamy in these societies.

Health Challenges of Endogamy

Endogamy has severe implications for the genetic health of populations. It can significantly impact the prevalence of genetic disorders via:

• Founder’s Effect – Occurs when a small group carries specific genetic mutations, which can become prevalent within the community due to intermarriage
• Genetic Drift – Refers to the random increase in frequency of specific genetic mutations within an isolated population

Understanding the complex relationship between endogamy and genetic disorders is essential for addressing health challenges within communities that practice it.

One of the most significant consequences of endogamous marriages is the higher risk of recessive genetic disorders. In an endogamous population, people are more likely to inherit two copies of a harmful recessive gene, leading to a genetic disorder.

These genetic disorders often remain hidden as carriers (people with one copy of the harmful gene) until they have children with another carrier, increasing the possibility of affected offspring.

How to Deal with Genetic Disorders in Endogamous Populations

Several necessary measures can be taken to tackle the health challenges associated with endogamy and genetic disorders.

Genetic Counseling

It is important to make genetic counseling available to people considering marriage within endogamous communities. This service helps them make well-informed decisions about family planning and assesses the risk of passing genetic disorders to their children.

Genetic counselors can offer guidance and support to couples.

Genetic Screening

It is also important to implement premarital genetic screening within endogamous groups. These programs aim to identify carriers of specific genetic mutations before marriage.

When both partners are carriers of the same mutation, they can make informed choices about marriage and reproduction. The couple can choose for genetic testing of embryos or consider alternative family planning options.

Risk Awareness

Another important approach to dealing with health problems associated with endogamy is to make more people aware of the risks involved. Educating people and groups empowers them to take steps to protect the health of upcoming generations.

This awareness can be spread through public campaigns that share crucial information and motivate people to get genetic testing when necessary.

These efforts ensure everyone has the knowledge to make informed decisions about their health and family planning.

Promoting Genetic Research

Backing genetic research in endogamous populations is important. Genetic research helps us understand how often genetic disorders happen and what causes them, especially in these unique populations.

When scientists study the genetics of these groups, they can detect trends and use that information to develop tailored solutions, like potential treatments or ways to prevent these disorders.

How Endogamy Affects Genetic Matching & Ancestral Research

Marrying within your group boundaries can make genealogical research easier or more complicated. It depends on the circumstances.

Genetic matching is usually more difficult for people without endogamous family relationships. They have to find eight sets of great-grandparents.

People who have endogamy in their families have it easier. They only need to locate fewer grandparents to confirm a genetic match.

The same couple will appear on multiple lines of their genealogy results.

Additionally, it’s easier to trace your family history when relationships are more insular.

For example, if your family was Acadian Catholic (an endogamous group), you can easily learn more about your heritage.

If you’re descended from religious groups who practiced endogamy and attended the same church, church records may be enough to identify your whole family.

It would be a different story if your ancestors practiced a religion that didn’t keep records. In these cases, endogamy does not affect your research.

What Happens When Records Aren’t Kept?

Without detailed record-keeping, it isn’t easy to make distinctions since the DNA matches tend to overlap.

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 in your family tree.

Not only do you share DNA with your cousin because her mother is your mother’s sister. You’ll also share DNA with 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.

Endogamy & Genealogical Relationships

In a standard DNA test, the company you send your sample to may not be able to determine that your family practiced endogamy. This is because endogamous populations cannot be easily distinguished.

A double first cousin would look like a half-sibling on paper. He/she will have the same amount of DNA you’d share with the same mother or father.

It’s even more complicated when this relationship is further back in your family tree and happened with your grandparents or great-grandparents.

And because endogamy rarely occurs once in a family, most people end up sharing more DNA with their cousins than is expected.

When marrying within a specific group, it can be challenging to determine genealogical relationships. DNA overlaps in your community, not because of one recent common ancestor but because you share multiple distant relatives in common.

Identifying Endogamous Relationships In DNA Results

One of the best ways to spot an endogamous relationship is to look at the DNA size and total amount of DNA you share.

Most DNA tests provide this information. You can examine the number of shared DNA segments and identify the largest DNA segment and its length.

If this seems complicated, your best bet is to take your DNA test results to a geneticist who can help you make sense of what you are looking at. A geneticist will assess your genetics and provide information on your genealogy. They also offer services that can help you analyze your genetics on your own.

It’s also important to consider the geographic location. Knowing where your ancestors lived may help rule out some groups. In some cases, a thorough genetic study, paired with efficient statistical analysis of available data, may be needed.

This is especially true for extended families with very limited information.