Should the UK government ban first-cousin marriage?
The recent proposal to ban consanguineous marriage in the UK has reignited a scientific debate that encompasses genomics, culture and personal freedoms
Marriage between first cousins, known as consanguineous marriage, has been practiced for centuries across many cultures – often seen as a way of preserving family wealth, strengthening social ties and maintaining cultural traditions. It is legal in most countries around the world, including in the UK; it has, however, long been the subject of scientific discussion.
The law
UK laws allowing first-cousin marriage date back to the reign of Henry VIII in the 16th century: having broken with Rome in order to marry Anne Boleyn, Henry passed a new law that enabled him to marry her cousin, Catherine Howard, four years after Anne’s execution.
The Marriage Act 1949 states that prohibited degrees of relationship in marriage include marriage to a sibling, parent, grandparent, child and grandchild. First-cousin marriage is not included, and the UK government states that it has no current plans to change the law.
However, Conservative MP Richard Holden believes the risks of first-cousin marriage are serious enough to justify a total ban. Speaking in parliament, he described it as a public health issue and a threat to women’s freedom, arguing that some women may be pressured into marrying their cousins.
“I have outlined the risks to health, freedom – especially for women – and the cohesion of our society,” Holden said. “For me, those risks tip the balance against personal freedoms.”
The concern around women’s rights in particular has been echoed in other parts of the world – including Norway, where cousin marriage was banned in 2024, with lawmakers claiming that it was linked to forced marriage and so-called ‘honour’ violence.
Genomic considerations
Each person carries two copies of most genes, one inherited from each parent. Many genetic conditions are recessive, meaning they only manifest when a child inherits pathogenic variants in both copies of the same gene. If a child inherits only one copy with the variant(s), they will be a carrier for the condition but will not develop it themselves.
Two first cousins will share around 12.5% of their genes, which increases the likelihood that they will both carry the same genetic variants. This, in turn, increases the chance of their children being born with a genetic condition.
In its recent coverage of new evidence around first-cousin marriage and child health, the BBC reported that more babies are being born with certain genetic conditions in Bradford – an area with a large British Pakistani population, in which first-cousin marriage is ‘fairly common’ – than in other parts of the UK. Professor Sam Oddie, who has worked with families affected by genetic conditions in Bradford for over 20 years, describes seeing families lose ‘several children, one after the other’ to the same genetic condition.
Is cousin marriage really the culprit?
However, Professor Oddie argues that to blame this phenomenon on first-cousin marriage is an “oversimplification”. Instead, he believes that the cause is a similar issue known as endogamy, in which people marry within the limits of their close community – though not necessarily blood relations. He explains that, even if exact family ties cannot be traced, in a tight-knit community certain genetic variants will occur more often, resulting in a higher chance of both parents having the same affected gene.
It must also be noted that, although children of first cousins have an increased chance of being born with a genetic condition, that increase is a small one: in the general population, a child’s chance of being born with a genetic condition is around 2%–3%; this increases to 4%–6% in children of first cousins. Hence, most children of first cousins are healthy.
The British Society for Genetic Medicine (BSGM) agrees that citing health as a reason to ban first-cousin marriage is not justified. It warns that, according to research, focusing on cousin marriage in this way stigmatises certain communities, undermines trust in medical services and causes couples to disengage from clinical support.
Responding to the proposed ban, the BSGM argues that the risks can be reduced through existing measures such as premarital genomic testing – which can identify carriers of certain recessive genetic conditions and is already offered in some countries (and, in certain regions with high rates of first-cousin marriage, is even mandatory) – as well as offering targeted health education and genetic counselling.
Balancing culture and science
Research into first-cousin marriage describes various potential benefits, including stronger extended family support systems and economic advantages (resources, property and inheritance can be consolidated rather than diluted across households). In addition, though first-cousin marriage is linked to an increased likelihood of a child having a genetic condition or a congenital anomaly, there are many other factors that also increase this chance (such as parental age, smoking, alcohol use and assisted reproductive technologies), none of which are banned in the UK.
Genetic counselling, awareness-raising initiatives and public health campaigns are all important tools to help families make informed decisions without stigmatising certain communities and cultural traditions. In order to balance respect for cultural practices with evidence-based healthcare, Professor Oddie stresses a focus on what he calls ‘genetic literacy’ – that is, education and voluntary screening – rather than simply banning the practice of first-cousin marriage.
