Why Europe Is Turning Against Cousin Marriage

Unlike the recent Scandinavian reforms, these laws were not introduced primarily in response to contemporary migration patterns or concerns about honor-based abuse, but formed part of broader family law designed to prevent consanguineous unions.

The Cost to Public Health

The principal case for a ban rests on health and genetics. The concern is not that every child born to first cousins will have a disorder. Most will not. Rather, closely related parents are more likely to carry the same recessive genetic mutation. If both pass it on, the likelihood of a child inheriting a serious genetic condition increases.

The best-known British evidence comes from the Born in Bradford study, which followed a large multiethnic birth cohort in West Yorkshire. Researchers found that first-cousin marriage remained a significant risk factor for congenital anomalies even after accounting for deprivation.

Data from the study showed that in three inner-city wards, 46% of mothers from the Pakistani community were married to a first or second cousin. According to the medical journal BMJ, congenital anomalies occurred in 6.1% of children born to first-cousin parents compared with 2.4% among children whose parents were unrelated.

For an individual couple the increased risk is measurable but not overwhelming. The broader concern is repeated cousin marriage over successive generations, which can concentrate inherited disorders within extended families.

Just one NHS trust in Birmingham has revealed that it spent $3.6m between 2020 and 2025 on treating patients with a “family history of consanguinity”. These figures emerged via a Freedom of Information request, as the NHS does not habitually publish data on the costs of such cultural practices. That number, however, suggests that millions must be spent every year.

Immigration, Integration and Social Cohesion

In Britain, however, the issue cannot be separated from immigration. Cousin marriage does happen but it is relatively rare. The exceptions are communities with family origins in Pakistan, parts of the Middle East, North Africa and among the Irish Travellers. Bradford has become the center of the debate because of both its large British Pakistani population and the extensive medical research carried out there.

It has been argued by critics that habitual cousin marriage can reinforce tightly knit clan structures, encourage bringing in foreign spouses and make it more difficult for younger family members, particularly women, to resist family expectations. Political parties like Reform therefore present the issue not only as one of health but also of integration and individual freedom.

Sweden's legislation reflects this broader approach. Rather than focusing solely on health risks, lawmakers explicitly linked the ban to honor-based oppression, coercion and forced marriage.

This might drive marriages into unregistered religious ceremonies, reducing legal protection for women. The legislation could also risk discouraging families from seeking genetic counseling. Many critics of the ban therefore favor increasing education, voluntary screening and community engagement instead of criminalization.

A European Tradition Older Than Immigration

Although cousin marriage is now largely discussed through the lens of immigration, Europe's opposition to the practice predates modern migration by more than a thousand years.

Beginning in the early Middle Ages, the Catholic Church progressively restricted marriage between close relatives. By the 11th century it prohibited unions within seven degrees of kinship, among the strictest marriage rules ever imposed in Europe. These restrictions were later relaxed at the Fourth Lateran Council in 1215 to four degrees of consanguinity, which still prevented first cousins from marrying without papal dispensation.

Many historians believe these rules reshaped European society by weakening extended kinship networks and encouraging smaller family units. Joseph Henrich, author of The WEIRDest People in the World, argues that the Church's marriage policies contributed to Europe's distinctive political and economic development by reducing clan loyalties and encouraging individualism, voluntary associations and stronger state institutions.

Following the Protestant Reformation, many countries relaxed these restrictions as civil law gradually replaced canon law. Britain legalized first-cousin marriage under the Marriage Act of 1540, and it has remained lawful there ever since. As the practice became increasingly uncommon among the native population during the 19th and 20th centuries, it disappeared as an issue from political debate until post-war immigration brought it back into public discussion.

Europe's Next Political Test

The central dilemma remains unresolved. Public health campaigns may reduce genetic risks over time, but they depend on trust and voluntary participation. A legal ban sends a clearer message but risks being viewed as an attack on particular communities.

Sweden’s decision nevertheless suggests that attitudes are shifting. Increasingly, Central and Northern European governments are willing to argue that some customs, even when defended as cultural or religious traditions, conflict with individual freedom, public health and social cohesion.

Britain and Austria may not follow Sweden immediately. Parliamentary time is limited and the Labour government has shown little enthusiasm for reopening another contentious debate linked to immigration. Yet the issue is unlikely to disappear. 

For decades lawmakers largely ignored the subject. Sweden's ban indicates that this period is ending, as increased immigration and its cultural consequences play a larger role in national life. The question facing Britain and other countries in Europe is no longer whether cousin marriage should be debated at all, but how best to tackle the issue.