The Frontal Cortex

The Incest Taboo and Kin Selection

There’s an interesting evolutionary psychology paper in the new Nature. It’s by Tooby and Cosmides, and it investigates the roots of the incest taboo. The researchers found that, on average, our repulsion at the idea of having sex with a sibling correlates with two variables: how long we lived with that sibling and how long we watched our mother care for that sibling (their “perinatal association”). We use these two variables to compute a “kinship index” that “corresponds to an estimate of genetic relatedness between self and other.” Siblings with a high “kinship index” not only triggered the incest taboo – the idea of having sex with them is disgusting – but exhibited increased altruistic behavior. That’s a nice proof of kin selection.


  1. #1 The Ridger
    February 15, 2007

    I recall reading somewhere, not that long ago, someone who pointed out that dynastic marriages (in China, I think it was) which involved bringing a very young child to live in the equally young spouse’s household until they grew up and were formally married often failed to produce offspring because the spouses regarding each other as kin, even though they weren’t.

  2. #2 David Harmon
    February 21, 2007

    Ridger: That was the Westermarck(sp?) study, it was mentioned in at least the SciAm article on this.

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