We’re all supposed to be born with an innate disgust for incest. It’s been put there by evolution to force us to leave the cave to find a suitable partner for having babies with. But for some people, that part of their brain is apparently broken. Whether mental illness or a phenomenon known as Genetic Sexual Attraction, here are six couples who committed the ultimate sexual taboo- having sex with, sometimes marrying and even having children with a close relative.

In June, 2004 Bruce McMahan eloped to England with his 35-year-old daughter. There was no wedding attire or officiant, but the couple exchanged rings at Westminster Abbey and posed for photos. Adopted at birth, Linda met Bruce for the first time in 1990, subsequently changed her last name to McMahan and began a sexual relationship with him in 1998. From there, Linda and Bruce decided to make their union official, despite the lack of papers, legality or a divorce from their prospective spouses. But after only a year, which was spent trying to hide their incestuous relationship, Bruce and Linda McMahan fell out after Linda refused to lie for Bruce’s divorce proceedings. Months of legal wranglings followed, with each party suing the other for everything from theft and extortion to defamation.

When this Australian couple were famously interviewed by 60 minutes in April 2008, the world took notice. John and Jenny Deaves didn’t have a typical father-daughter relationship after the divorce between John and his daughter’s mother, though Jenny did sporadically spend time with him growing up. They reconnected in 2000 and both John and Jenny left their spouses to live together as a couple. They’ve had two children together, one dieing shortly after birth from a heart defect, and were arrested and charged with incest by an Australian court. After pleading guilty the Deaves were released by the courts, provided they stop the sexual part of their relationship, which they claimed they curtailed for fear of a prison sentence. The couple has since separated.

Danielle and Nick didn’t grow up as brother and sister. Raised in foster care, Nick Cameron met his half-sister Danielle when she was twenty and he 26. After three weeks of knwoing each other they began a sexual relationship but were reported to authorities by their mother who walked in on them having sex. Incest in their native Scotland is a felony, and Heaney and Cameron were sentenced to nine months probation where they could not have verbal or physical contact. They now live together but claim to not be sexually intimate. When they were last interviewed the pair were contemplating a move to France, where incest is not a crime.