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Kissing Cousins: Why Haven’t Arranged Marriage Laws Reduced Human Genetic Diversity?

Credit: Elka Lesmono

Credit: Elka Lesmono

By Murray Cox

Many traditional communities, including our ancestors, have long enforced marriage between first cousins. Why hasn’t this had a negative impact on genetic diversity?

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In the middle of the rainy season in 1975, cultural anthropologist Gregory Forth walked into the village of Rindi on the small island of Sumba in eastern Indonesia. For 2 years he studied the social rules, ethnography and environment of this remote community, including the cultural meaning of their distinctive house styles and megalithic monuments. He also recorded their intricate customs and rules around marriage.

Rules that dictate who we can and cannot marry were once more common than they are in western societies today. Our rules are now typically few: you cannot marry your siblings, but you can usually marry your cousin. (Although frowned on by many, including some religions, the only country in the western world to actually outlaw first cousin marriage is the United States. Even there, the rules vary widely: you can marry your first cousin in California but not in Mississippi). In contrast, the rules prescribing options for marriage partners in most traditional societies are far more ornate.

In Rindi, people follow a particularly complicated set of rules that date back centuries. A man must marry his first cousin, but only on his mother’s side. Communities are subdivided into clans, with a woman moving to the clan of her husband after marriage. Clans are further structured into “wife-giver” and “wife-taker” groups.

Generation after generation,...

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