*Some names have been changed to protect identity.

Casey is proud of his 23-year marriage to Sara, but he wants to clarify something straight away: “I don’t have any other cousins I’m attracted to, and I never decided consciously to pursue my cousin.”

The couple, who are from North Carolina in the US, met properly for the first time as teenagers. There was immediate chemistry, but Casey’s father and Sara’s mother are siblings, so for five years neither acted on their desires. When they finally did, it evolved into something they “couldn’t ignore”, so when he was 22 Casey proposed to Sara.

His family were shocked. “I had one uncle tell me I deserved to be in a ditch and my dad told me I’d end up in jail, but that all died down once we got married,” Casey says. “There are uncles I still don’t speak to, but they didn’t like me before the relationship either.”

“Even I was surprised that it’s happened,” he adds. “But besides the fact we’re first cousins, it’s an entirely normal relationship.”

The couple are now more open about the fact they’re related, but Casey only ever told one friend when he and his wife were dating. “There was a sense of shame and a fear that people would say we’re wrong,” he says, “and that was something I struggled to deal with.”

The idea of romantically or sexually involved cousins is generally met with distaste. It’s family; you don’t have sex with family. Despite this, cousin relationships, known as consanguineous relationships, are a “deeply rooted trend” among one-fifth of the world’s population, especially among Muslim regions in parts of South Asia and the Middle East, where consanguineous relationships can make up 30-50 percent of entire communities.

The practice is less common in the West, but consanguineous relationships in Europe and the United States were common until the mid-19th century, when attitudes began to turn on the practice due to medical opposition.

“In terms of the global population, more than a billion people are born and live in communities where 20-50 percent of the marriages are to [at least] a second cousin,” says Alan Bittles, Research Leader in the Centre for Comparative Genomics at Murdoch University.



Bittles, who has been researching consanguineous relationships for more than 40 years, says this means 10 percent of the world’s population are consanguineous, at a minimum. “A lot of countries like Indonesia, Bangladesh and Sub-Saharan countries [lack] data, as well, so that figure is most likely a lot higher.”

“On a cultural level,” Bittles says, “there’s no reason why we shouldn’t accept it in our society.”

Few religious texts or national legislations explicitly ban consanguineous relationships. In Australia, it’s perfectly legal to marry your first cousin (or your niece, nephew, aunt or uncle). But the act is still taboo, particularly in the West.

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“It [the stigma] all boils down to this fear of birth defects and having a kid with two heads,” Casey says, “but that’s just ignorance. We’re trying for kids at the moment, and we know there’s nothing to worry about.”

Having a child with a cousin does appear to pose a risk of a potential recessive trait in your genes surfacing. But, says Dr Greg Jenkins, an obstetrician at Auburn Hospital who has seen at least 4,000 babies born of consanguineous relationships, the risk of congenital defects is lower than you might think.

“The data we’ve got from Auburn Hospital shows there’s a two- to three-fold increase in congenital defects and a two-fold increase in stillborn deaths in consanguineous relationships,” says Dr Jenkins. “With two percent of all births having some type of congenital abnormality, consanguineous relationships are something like five to six percent. So 94 percent of [consanguineous] births are fine and healthy babies.

“So we’re talking small numbers, but it’s a ‘bigger’ small number if you’re in a consanguineous relationship,” he says, adding, “I don’t think we should be telling people that they shouldn’t be reproducing with their first cousin. I think the better work we can do [is] educate couples about the risks associated with it.”

Attitudes against cousin marriage aren’t always exclusively genetic: community and religion can also drive opposition. This was the case for 20-year-old Devleena, who has been in a relationship with her father's sister's son for three years, and whose community in New Delhi is against the idea. In parts of India cousin marriage does happen and is accepted, Devleena says, “[But] I’m Hindu, and in our religion the attitudes are more community-specific.”



Like Casey and Sara, Devleena and her cousin met as teenagers; soon after, her cousin professed his love for her, and one year later they started a relationship. At first they both felt anxious that it would tear the family apart, she says. “Our family isn’t happy about our relationship. My parents aren’t violent [but they] say mean things to me all the time and they wish to arrange a marriage for me, but I refuse.”

“Once I move in with him, I know I’ll never see my family again,” Devleena continues. “It can be scary to be in these relationships though, because honour killings do happen over this. I’ve had friends in relationships with their cousins who’ve had death threats from their parents”

Despite staunch opposition from her parents and her community and the very real threat of honour killings, Devleena does have support from friends in the same position as her. She knows 15 other consanguineous relationships through social media and real life, including two in her own social circle. Most importantly, she has her partner, who she tells me will fight for their relationship.

“I don't think I would be against any form of consensual relationship," Devleena says. “Love is love.”

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This article originally appeared on VICE AU.