How Many People Are Married to Their Cousins Right Now?

Illustration for article titled How Many People Are Married to Their Cousins Right Now?

Friday’s an excellent day for fun facts, and this week’s excellent and important piece of information comes from FiveThirtyEight’s Ask Mona column which answers the important question of how many people are not just kissing, but wedding their cousins in the United States.


The question, asked by an Australian named Daryn—who’s making fun of ‘muricans, I presume—is actually one of those things that’s really interesting. We know that marrying your first cousin is illegal in some states (still totally kosher in California and Florida, in case you were wondering, but you can’t even marry an adopted cousin in Texas), but how many people are getting hitched anyway, maybe even moving to more permissive states to exercise their love?

Mona Chalabi’s answer is long, very sensitive, and incredibly detailed. (I kind of expected her to write something like, “Ten. Ten people are married to their cousins. Next.”) You should read the entire thing for yourself here, but if you don’t have time for facts and maps and conversations with researchers who study genetics, here are some numbers for you:

An estimated 0.2 percent of marriages in the United States are between individuals who are second cousins or closer — that means there are about 250,000 people in America in those relationships. I know you asked about first cousins, but all the research I’ve found uses second cousins as the benchmark of consanguinity (more commonly known as intermarriage). A brief reminder here, Daryn, if, like me, you get confused about who is a second cousin: It’s someone who shares a great-grandparent with you.

Other fun facts you should know: Cousin marriages occur at a higher rate in Australia (FACE, Daryn), and that if you’re worried about marrying your cousin in Iceland, there’s an app for that.

Maybe, though, Daryn, you’re uncomfortable with the notion of a romantic relationship with a first cousin, or anyone with whom you have a high inbreeding coefficient. If so, this app developed in Iceland (a country with a small population where naming conventions make it hard to figure out who’s related by blood) may be of interest to you. The “incest spoiler” uses a genealogical database so users can check if they’re related before hooking up.

“Incest spoiler.”

Image via FOX.

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Thanks for bringing this up. 10% of marriages worldwide are between first cousins. My aunt married her first cousin (her daughter is my first and second cousin). My great grandparents were cousins. More than one president has married his cousin. Cousin marriage is far more common among people from some parts of the world, making our unwarranted prejudice against the practice a form of xenophobia. The only reason first cousin marriage is illegal in some states is an obsession in the early 20th century with eugenics, which, among other things, also fostered Nazism and racism. Actual study of the incidence of mutation in first cousin couples demonstrates that it is less than or the same as the risk of mutation in women over 40. It makes no more sense to criminalize first cousin marriage than to criminalize pregnancy over age 40.

Do some families with homozygous disorders have higher potential risk of disease? Yes. They should seek genetic counseling and may benefit from IVF and embryo selection and/or in utero screening and termination.