Marriages between cousins, also known as consanguineous marriages, have been quite common throughout history, especially in small communities where options are slim when it comes to potential spouses.
But this also happens today: from 2022, more than 10 percent of marriages worldwide were between first or second cousins.
“In some situations, especially in island communities, marriages between distant and not-so-distant cousins have been celebrated many times over many generations,” Bakkala says. “In these cases, their descendants often have more than one relationship to each other. It is possible, and indeed not uncommon, for two people to be, for example, fourth cousins and sixth cousins once separated at the same time. In two ways different produces two different results.
Although it is not that rare, marrying your cousin is extremely taboo in some places. In some countries (including China, Taiwan and the Philippines) marriage between cousins is completely prohibited.
In the US, some states outlaw sexual relations, cohabitation or marriage between cousins, and some prohibit all three. Some states like Arizona and Indiana ban marriage between cousins in those under 65 years of age.
Although consanguineous children are reputed to have high mortality rates, mortality in the offspring of first cousins is about 3.5 percent higher than in children whose parents are not cousins. And even if children of cousins survive, there are other genetic considerations to take into account, such as a greater likelihood that recessive genetic traits will be expressed in their offspring.
This article was updated along with artificial intelligence technology, then verified and edited by a HowStuffWorks editor.