Cousin Marriage: Pros, Cons, and Genetic Risks

Cousin marriage, a form of consanguineous marriage, is a marriage between close relatives, up to second cousins. It’s a union between people who are related by blood. The practice has existed in many cultures for religious, political, and kinship reasons; however, its prevalence and level of acceptance vary across communities.¹Cousin marriage. (2025, August 30). In Wikipedia. Retrieved August 30, 2025, from https://en.wikipedia.org/wiki/Cousin_marriage

Consanguineous marriage refers to a union between blood relatives, generally second cousins or closer, but it also includes other close-relative unions, such as uncle-niece marriages. While consanguineous or close-cousin marriage may offer some social benefits where it is practised, it also increases the risk of certain inherited disorders in children, some of which can be life-threatening.²Khayat A M, Alshareef B, Alharbi S F, et al. (February 09, 2024) Consanguineous Marriage and Its Association With Genetic Disorders in Saudi Arabia: A Review. Cureus 16(2): e53888. doi:10.7759/cureus.53888. The pros and cons deserve special attention, especially if you are planning to have children.

Thus, whether you are considering marrying a cousin or simply want to understand the practice, this article examines its reported benefits, potential disadvantages, and genetic risks to help you make an informed decision.

Pros and Cons of Cousin Marriage

The table below summarises reported social benefits and potential disadvantages. These outcomes vary between couples and communities; social benefits do not remove reproductive risks.

Table showing the pros and cons of cousin marriage.

Difference Between First and Second Cousins

Your first cousins are the children of your aunt or uncle, meaning one of your parents is the other’s sibling, and you share grandparents. They are also referred to as first-order cousins and share about 12.5% of their DNA.³Genealogy Explained. (n.d.). How much DNA do first cousins share? https://www.genealogyexplained.com/how-much-dna-do-first-cousins-share/

Second cousins are children who share the same great-grandparents but not grandparents. Their parents are first cousins to each other, and their grandparents are siblings.

There are several orders of cousins, such as third-order, fourth-order, sixth-order, and beyond, but children of first-order cousin unions have the highest (4-6%) reproductive risks, including stillbirths, infant mortality, and birth defects. These risks generally decrease with higher-order cousin relationships, but an individual cousin-couple’s risk may also depend on their family history and whether they carry variants for an inherited condition.⁴Hamamy H. Consanguineous marriages: Preconception consultation in primary health care settings. J Community Genet. 2012 Jul;3(3):185-92. doi: 10.1007/s12687-011-0072-y. Epub 2011 Nov 22. PMID: 22109912; PMCID: PMC3419292.

Can First or Second Cousins Marry?

Marrying your first or second cousin is not inherently wrong, but this depends on your personal and religious beliefs, cultural expectations, and the marriage laws where you live. Some cultures and religious contexts may permit close cousin marriages, while others may not. Free consent from both individuals is also important.

Having children with a second cousin generally carries a lower additional genetic risk than having children with a first cousin. This may explain why some cultures condemn the practice. However, if you are considering marrying and having children with a first or second cousin, it can help to review your family history with a genetic counsellor to clarify the risks and whether additional testing would be required.

Potential Benefits of Cousin Marriage

Consanguineous marriage, of which cousin marriage is a type, has been practiced mainly due to social reasons. Notable individuals in history who married a close cousin include Charles and Emma Darwin (first cousins), Saddam Hussein and Sadija Talfah (first cousins), Albert Einstein and Elsa Lowenthal (first maternal cousins and second paternal cousins), Franklin and Eleanor Roosevelt (fifth cousins once removed)⁵”Once removed”; meaning separated by one generation. MyHeritage, and Thomas Jefferson and Martha Wayles Skelton (third cousins).

Here are some potential benefits of cousin marriage.

1. Better relationship between a partner and in-laws

One of the potential benefits of marrying a close cousin is that it sustains a cordial relationship between a partner and in-laws. This was also in keeping with a Pakistani study on consanguineous marriage, which showed that the majority of respondents experienced a better and more caring attitude from the in-laws, and it was easier for new brides to adjust to their new family.⁶Hussain, R. (1999). Community perceptions of reasons for preference for consanguineous marriages in Pakistan. Journal of Biosocial Science, 31(4), 449–461. https://doi.org/10.1017/S0021932099004496⁷HandWiki. (2022, October 12). Cousin Marriage. In Encyclopedia. Retrieved September 2, 2025, from https://encyclopedia.pub/entry/28985

2. Familiarity with a partner and their family

Authors have also cited that some people believe that marrying within the family may mean fewer surprises about a partner’s health history and financial circumstances. However, while there may be some familiarity, this does not guarantee full transparency about undiagnosed illness or financial difficulties in all cases.⁸Ibid. Hamamy H. Consanguineous marriages: Preconception consultation in primary health care settings. J Community Genet.

3. Existing family support

Some cultures value maintenance of physical closeness between relatives. In these situations, marrying a close cousin may potentially strengthen the family ties between a wife and her relatives-in-law.

In many cultures, a wife’s parents prefer to have their daughter living near them, so as to enjoy the presence of their grandchildren. To facilitate marriage between close relatives, families may conduct premarital negotiations more easily and sometimes less costly.⁹Ibid. Hamamy H. Consanguineous marriages…

4. Preservation of cultural values

It is also believed that consanguinity may enhance family solidarity and provide excellent opportunities for the transmission of cultural values across generations. With both partners already familiar with their family’s customs and traditions, they may find it easier to maintain shared practices and pass them on to their children. However, these benefits are not exclusive to cousin marriages.

5. Keeping property within an extended family

Families with significant assets may encourage consanguineous marriage to keep property within the family. This way, family wealth, such as land, businesses, or inherited assets, may consequently remain under the ownership of relatives across generations. However, this may depend on property inheritance laws and the couple’s decisions, and not necessarily on cousin marriage alone.

Disadvantages and Risks of Cousin Marriage

Cousin marriage may have the following disadvantages and risks.

1. Increased risk of certain inherited disorders in children

Children born to first- or second-cousin couples are at a higher risk of some inherited diseases, including Tay-Sachs disease, cystic fibrosis, and sickle cell disease. These genetic diseases have an autosomal recessive pattern, meaning they require two copies of the gene to produce the disease condition.

In families where this gene exists in individuals as a single copy, cousin marriage may increase the chances of giving birth to a child(ren) with both copies of the gene, leading to the disease.

2. Potential family pressure and reduced freedom of choice

In communities where cousin marriage is strongly preferred, individuals may face family pressure in their choice of a partner. Parents or relatives may favour a cousin. making it difficult to refuse without fear of disappointing the family or causing a conflict.

3. Relationship conflict affects the wider family

Marital conflicts in a cousin marriage may be harder to keep separate from existing family relationships. Because both partners belong to the same extended family, relatives may feel pressured to take sides or get involved in private disputes. This can create wider tensions and complicate family relationships.

4. Possible reduction in birth weight

A 2007 study in Lebanon found that babies born to consanguineous couples had slightly lower birth weights for their gestational age than those born to unrelated couples. The findings showed an estimated reduction of 1.8% in birth weights; however, it does not mean that every baby born to related parents will have a lower birth weight.¹⁰Mumtaz, G., Tamim, H., Kanaan, M., Khawaja, M., Khogali, M., Wakim, G., Yunis, K. A., & National Collaborative Perinatal Neonatal Network. (2007). Effect of consanguinity on birth weight for gestational age in a developing country. American Journal of Epidemiology, 165(7), 742–752. https://doi.org/10.1093/aje/kwk108

What To Consider Before Marrying a Cousin

Before marrying a first or second cousin, here are some important factors to consider.

• Free and informed consent: Both partners should freely choose the marriage without pressure from relatives or cultural expectations.
• Local marriage laws: Check whether your relationship falls within the legally permitted degree where you intend to marry and live. Some marriage laws permit cousin marriage up to the third-cousin degree.
• Plans for children: Discuss whether you want biological children and the potential risks from the marriage towards childbearing. This should be included in the questions to discuss before marriage.
• Family health history: Are there any known inherited conditions, birth defects, or unexplained childhood deaths in either partner’s family? Some inherited conditions can be expressed in children born to consanguineous partners.
• Genetic counselling and testing: A genetic counsellor can review your family history, explain reproductive risks, and advise whether carrier testing would be useful.

Historical Perspectives of Cousin Marriage

Historically, while some cultures forbade cousin marriage, others permitted it for various reasons. Changing laws also affected the acceptance of cousin marriage globally, as we see here.

Europe – Preservation of Family Wealth and Alliances

One of the major reasons why early Europe encouraged close cousin marriage was for the consolidation of family wealth and alliances. But cousin marriage soon became prohibited as the laws evolved.

The Roman civil laws in early medieval Europe allowed close cousin marriage. The Justinian reforms in the 6th century CE prohibited it up to the fourth cousins, and by the 9th century, the Justinian Code adopted by the Catholic church had extended the ban up to the sixth cousins.¹¹Wikipedia contributors. (2025, August 29). Cousin marriage. In Wikipedia. Retrieved September 2, 2025, from https://en.wikipedia.org/wiki/Cousin_marriage

By the 11th and 12th centuries, it became nearly impossible to find a spouse who wasn’t within the forbidden degrees. Due to this, the Fourth Lateran Council of the Catholic church revised the prohibition to allow fourth-cousin marriages in 1215. This demonstrates how changing laws affect the acceptance of consanguineous marriage in human societies.

Asia (China) – Maintenance of Family Boundaries and Kinship Roles

Ancient Chinese communities subscribed to Confucian values that marriage is a union between two surnames. This is to maintain proper family boundaries and avoid confusion in kinship roles.

However, while that significantly prevented close-cousin marriages, it permitted cross-cousin marriages, where one can marry a child of a parent’s opposite-sex sibling (that is, one’s father’s sister’s child or one’s mother’s brother’s child). Cross-cousins had different surnames and did not disrupt sibling-like roles within the extended family.

Later, during the Ming Dynasty (14th to 17th century, all cousin marriages were prohibited by Chinese law. During the Qing Dynasty (17th to 20th century), the former law was restored, once again allowing first-cousin marriages. Eventually, mid-20th century anthropologists noticed that cross-cousin marriage had become generally obsolete, termed as “permitted but not encouraged”.

In 1981, the government of the People’s Republic of China enacted a legal ban on first-cousin marriage due to potential health concerns. This prohibition was retained in the revised Marriage Law of 2001 and the Civil Code of 2021, which is still in effect to this day.

Unlike mainland China, Hong Kong and Macau, which are Special Administrative Regions of China, do not prohibit marriage between first cousins solely because they are cousins.¹²Immigration Department. (n.d.). Marriage registration. The Government of the Hong Kong Special Administrative Region. Retrieved October 16, 2026, from https://www.immd.gov.hk/eng/faq/marriage-registration.html

Middle East – Traditional Kinship System

Cousin marriage has been allowed throughout recorded history of the Middle East. Some anthropologists view this as the defining feature of the Middle Eastern kinship system, while others have opined that the rate of acceptance is not the same across the entire Middle East. The tradition likely originated in ancient times when tribes relied on their cohesion during periods of movement and nomadism, Dr. Assel Aljaied opined.

According to the accounts of Raphael Patai, a Jewish anthropologist, in Central Arabia, a man has a customary preferential claim to marry his father’s brother’s daughter (FBD). The girl is not forced to marry her male cousin, but she requires his consent before marrying another man.¹³Patai, R. (1962). Golden river to golden road: Society, culture, and change in the Middle East. University of Pennsylvania Press.

This custom is pervasive in the Middle Eastern and Arab countries, including Jordan, Iraq, Syria, Qatar, Yemen, the UAE, etc. Deeply rooted in kinship traditions and as a social institution tied to property, inheritance, and clan solidarity, consanguineous marriage in some of these countries is among the highest reported rates worldwide. However, this prevalence varies considerably across the region.

Africa – Religious Considerations of Cousin Marriage

While the exact rates of consanguineous marriage in Africa are unknown, cousin marriage in this continent is largely influenced by religion. However, it has been estimated that 35–50% of sub-Saharan African populations either prefer cousin marriage or accept the practice.¹⁴Bittles, A. H. (1994). The Role and Significance of Consanguinity as a Demographic Variable. Population and Development Review, 20(3), 561–584. https://doi.org/10.2307/2137601

African Traditional Religion (ATR), Christianity, and Islam are the major religions in the African continent, and these have their respective views on cousin marriage.

ATR forbids cousin marriage up to around the fourth-cousin degree, and particularly links close cousin marriage to a taboo. In some areas, special atonement rites are done to permit close cousin marriage if the marriage must be consummated. It is believed that these rites help to lift curses that may come from intimate relationships between close relatives.

Attitudes towards cousin marriage vary among Christian communities in Africa. This may reflect church teachings, local kinship customs, or a combination of both. Some communities discourage or prohibit close-cousin marriage, while others accept it under special circumstances.¹⁵Shawky, R. M., El-Awady, M. Y., Elsayed, S. M., & Hamadan, G. E. (2011). Consanguineous matings among Egyptian population. Egyptian Journal of Medical Human Genetics, 12(2), 157–163. https://doi.org/10.1016/j.ejmhg.2011.07.001

Among Muslim communities in Africa, Islam permits cousin marriage, but this does not translate into a preference for it. Local kinship traditions and family expectations also shape the acceptance of close relative marriages significantly.¹⁶Egypt’s Dar Al-Ifta. (2015, March 15). Arranged marriages between cousins: Is it recommended? https://www.dar-alifta.org/en/fatwa/details/8196/arranged-marriages-between-cousins-is-it-recommended

The Americas – Social Order and Genetic Reasons

In the United States, even though consanguineous marriage was not legally prohibited, several attempts have been made to ban the practice, for reasons including maintenance of social order, religious morality, and to safeguard the creation of fit and viable offspring.¹⁷Ibid. Wikipedia

Writers like Lewis H. Morgan (1818-1881) wrote on topics like “The advantages of marriages between unrelated persons” and “The necessity of avoiding the evils of consanguine marriage” to argue against close-cousin marriage.¹⁸Ibid. Wikipedia. Cousin Marriage.¹⁹Ottenheimer, M. (1996). Forbidden relatives: The American myth of cousin marriage [Archived webpage]. Urbana: University of Illinois Press. Retrieved September 3, 2025, from https://archive.org/details/forbiddenrelativ00otte/page/n5/mode/2up

In 1846, George N. Briggs, then Governor of Massachusetts, appointed a commission to carry out a study which implicated cousin marriage as being responsible for idiocy in offspring of these unions. Several other reports supported that cousin marriage could lead to deafness, blindness, as well as idiocy. Perhaps the most important was the report of the Physician, Dr. Samuel M. Bemiss, which was of the conclusion that cousin inbreeding can lead to physical and mental deprivation of offspring.²⁰Ibid. Ottenheimer. 1996

Even though later scientific discoveries had refined these conclusions, those findings led to the passing of cousin marriage prohibitions in 13 states of the United States in the 1880s. Before the end of the 1920s, the number of states had doubled. By 1985, genetic counselling and possible genetic screenings were mandated for marrying cousins to minimize reproductive risks to their children.

Frequently Asked Questions

Final words

Cousin marriage involves social, cultural, legal, and reproductive considerations. Social benefits such as familiarity and family support may be valued benefits, but these are not guaranteed and are not exclusive to cousin marriages.

Before marrying a cousin, both partners should freely choose the relationship and understand the applicable marriage laws. If they plan to have biological children, reviewing their family history with a genetic counsellor can help clarify reproductive risks and determine whether testing would be useful.