In 1870, Charles Darwin, tormented by the idea that his marriage to his first cousin might be the cause of his children’s ill health, asked his friend Sir John Lubbock to take the matter to Parliament. Lubbock was to propose that the national census include a question on cousin marriage. As Darwin wrote, cousin marriage was often objected to for fear of its “supposed injurious consequences”, though this belief rested “on no direct evidence”. Darwin thought that the suspicion should either be proved wrong, or else confirmed so that “the marriage of cousins might be discouraged”. But when he raised the idea in the Commons, Lubbock was apparently laughed out the room. The House believed that cousin marriage was perfectly respectable, and it was far more concerned with debating the question of whether a man should be allowed to marry his deceased wife’s sister.
Today, Darwin’s conundrum has returned to Parliament. Richard Holden, the MP for Basildon and Billericay, has proposed a bill to ban first-cousin marriage in the UK. While the bill is highly unlikely to pass, it follows similar debates in Sweden, Norway, and Denmark, and reflects a swelling interest in the subject on the British Right. According to Holden, cousin marriage creates problems in three areas: health, freedom, and our national values. Muslim communities, particularly Pakistani ones, have been at the centre of these debates due to their high rates of cousin marriages. Around 27% of the women in the most recent cohort (2016-2019) of the “Born in Bradford” study were married to their first cousin.
Is this sudden interest in cousin marriage driven by genuine concern for the communities involved? Or does it — intentionally or not — fuel anti-Muslim sentiment, fostering division by presenting cousin marriage as an unnatural and foreign practice?
“Is this sudden interest in cousin marriage driven by genuine concern for the communities involved?”
Cousin marriage isn’t unnatural: it has been practised around the world for thousands of years. But could it pose a health risk to the resulting children? If Darwin were alive today, he might be surprised to discover that, despite our better understanding of genetics, significant gaps in our knowledge remain. Roughly, the baseline risk of unrelated parents having a child with a major birth defect is 3%; for a child of first cousins, this risk increases to 6%. This means that the vast majority of children born from consanguineous marriages will be healthy. Of course, if there are known genetic disorders within the family, then this risk increases, and successive generations of cousin marriage can also compound the likelihood of having a disabled child — but this is by no means inevitable.
Nevertheless, these additional risks can be offset through prenatal genetic screening, which is currently offered to other at-risk groups. Older pregnant women, for example, are screened for Down’s syndrome, as are couples who are carriers of cystic fibrosis. We don’t ban these individuals from marrying or having children, and we don’t consider them a burden on the healthcare system.
Nor is it only the children of cousins who are at risk. The likelihood of health problems is increased whenever there is a higher chance that two individuals share genes. This can occur in small populations or in any close-knit community that marry among themselves — such as the UK’s Jewish community, or else the Amish in America or French Canadians. Would Holden also support banning marriage within other ethnic communities? I suspect not.
Beyond birth defects, the risks of cousin marriage are difficult to calculate. The Bradford study suggests that consanguineous children access health care at higher rates, and may also struggle more at school. The children of unrelated parents have a 7.4% probability of having speech and language difficulties; this figure rises to 11.3% for the children of first cousins. Yet we shouldn’t leap to conclusions. One issue with this analysis is that cousin marriage often correlates with poverty, which has an independent effect on health. Many of the areas in Britain with high rates of cousin marriage are extremely deprived, and while this analysis does control for poverty, it is unlikely to capture all aspects of socioeconomic disadvantage — making it unclear the extent to which genetics ultimately matter.
Holden’s second argument against cousin marriage — that it undermines the freedom of women — is similarly simplistic. He, along with other commentators including journalist Matthew Syed and researcher Patrick Nash, suggest that cousin marriage is often forced and harmful to women. They argue that cousin marriage produces a “clannish” inward-looking culture, which leads to strict control over the behaviour of group members. In the case of women, this can mean having no choice over their husbands, and being subject to honour codes that dictate appropriate female behaviour. Nash even argues that clan institutions are “known to condone abuses [including] spousal violence”.
Firstly, there are many forced marriages that do not involve cousins. So why target them indirectly via a ban on cousin marriage? That aside, the relationship between cousin marriage and women’s freedom is far more complex than Holden implies. There is a large body of research that suggests that exogamous marriage — that is, marrying outside one’s community — can actually damage a woman’s status and undermine her freedom. Across the world it has been, and still is today, much more common for women to move away from their natal kin to live near her husband’s kin. When a woman marries “out”, she often leaves her support networks behind; in moving into her husband’s household, she enters a community where she has little established status, reputation, or family protection. This isolation can reduce her bargaining power, and without nearby family support, she becomes vulnerable to exploitation by her husband and in-laws.
But when a woman marries her cousin, this separation from family doesn’t happen: and she may have greater status than if she hadn’t. In a survey from Bangladesh, almost 80% of respondents say that a key benefit of cousin marriage is that wives have influence over their in-laws. Men say something similar. In Lila Abu-Lughod’s 1986 ethnography of Egyptian Bedouins, men described how they could trust their cousin-wife because they “care about you and your things because they are hers” and that “after all she is my father’s brother’s daughter”.
These dynamics have been shown to protect women. In studies of domestic violence, including my own, women married to their cousins report less intimate-partner violence. This is arguably because the family connection creates accountability that may not exist in marriages between unrelated individuals. Though the results could also reflect a hesitancy to admit to domestic violence. Nonetheless, it is overly simplistic to say that cousin marriage is inherently oppressive to women, and it is telling that even when individuals have free choice over their marriage, many still choose cousins as partners, as documented in Bangladesh.
But let’s be clear: cousin marriage typically occurs in conservative communities, where women frequently have low status and where interaction between men and women is restricted. For women navigating these environments, marrying a cousin can provide a degree of certainty and security in an otherwise potentially risky proposition. For many, it could be a strategic choice. The critical question — does cousin marriage create gender restrictions or simply exist alongside them? — is rarely addressed by those who condemn the practice.
Yet as mentioned, critics like Nash and Syed argue that cousin marriage not only encourages domestic violence, but also creates honour codes that can lead to honour-based violence — a punishment enacted for dishonouring the family through actions that can range from leaving the house without a male chaperone to premarital sex. It differs from intimate-partner violence, in that it is often perpetrated by a woman’s immediate family, such as her father, brothers, uncles, and cousins. My own research has tested this association, and finds that societies that have practised higher rates of cousin marriage also tend to have stronger honour cultures.
Yet this connection should not determine modern policy, for several reasons. Firstly, even if cousin marriage historically contributed to the emergence of honour systems, banning it won’t necessarily dismantle them. Cultural norms can persist independently of their origins — and if men are intent on controlling the behaviour of women, and the honour code is a useful tool with which to do that, then they will continue to use it. This might explain why, even as cousin marriage rates have declined around the world, honour codes have remained entrenched.
Neither has this theory been proven beyond a reasonable doubt. It is certainly not established enough to justify restricting personal freedoms, and much like many singular theories of human culture, is unlikely to ever be. Anyway, basing individual rights on scientific theories is fundamentally problematic; all theories should remain open to challenge and revision, and are unsuitable foundations for determining laws — as these very laws would be undermined as science gets updated.
In the end, emotive calls to ban cousin marriage accomplish little beyond sowing distrust towards certain ethnic groups. Concerns relating to health and violence against women would be better tackled by other policy levers. That would leave the intimate decision of marriage up to the individual, rather than the state.
