Cousin Marriage OK by Science

In an age of sexual liberation, marriage between cousins remains taboo, at least in the United States — and from a scientific perspective, laws against the unions are a socially legitimized form of genetic and sexual discrimination.

That argument, raised Monday in an editorial in Public Library of Science Biology, may turn the stomachs of people raised to disapprove of any form of incest. But dispassioned analysis suggests that cousin marriage is no more troubling than childbearing by middle-aged women.

"Women over the age of 40 are not prevented from childbearing, nor is anyone suggesting they should be, despite an equivalent risk of birth defects," write zoologists Hamish Spencer and Diane Paul. Bans against cousin marriage, they say, should be repealed, "because neither the scientific nor social assumptions that informed them are any longer defensible."

Thirty-one states outlaw marriage between first cousins, making the United States the only developed country in which the practice is regularly banned. Most were passed in the Civil War's aftermath — not, say Spencer and Paul, to reduce the chance of defects caused by combination of deleterious genes, but as part of a radical expansion of government authority over private lives.

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