NewScientist.com reports (found via Marginal Revolution; see also Catallarchy) that “according to a study published this week, up to 45% of the differences between women in their ability to reach orgasm can be explained by their genes.” The study compared the similarity in orgasm frequency, as reported by respondents to a questionnaire, of identical and non-identical twins. This is my guide to interpreting these results:
1. If you are already convinced that people differ in this kind of traits due to genetic differences, and not to environmental differences, and so you do not really need scientific studies to make up your mind, then you can skip the remainder of this post.
2. NewScientist.com says: “The idea behind twin studies is that pairs of twins grow up in similar environments. So if identical twins are more similar in some way than non-identical twins, then that similarity must be down to their identical genes rather than the environment.” Wrong. It may be that identical twins share a more similar environment than non-identical twins. You may ask, why? I may reply, why not? It is Rowan Hooper of NewScientist.com, not me, who is stating something about the environments of twins. Anyway, I will suggest two possibilities. First, maybe relatives and friends expect identical twins to behave identically and this leads to overly similar experiences for identical twins. For example, parents decide that two six-year-old identical twins take basketball lessons (or both take soccer lessons) instead of one of them taking basket and the other soccer, because they expect identical twins to share similar preferences for sports. Second, maybe identical twins show certain similar behaviors due to some genes they have in common (for example, two twins play basketball because both are tall, which may be due in part to identical genes) and these similar behaviors create further environmental similarities (for example, they share the same circle of basket-playing friends). These environmental similarities may in turn produce similarity in behaviors whose variation has nothing to do with genes.
3. Still, you may be convinced that this sort of environmental similarities, which may occur more often between identical than between non-identical twins, cannot possibly explain the higher similarity in orgasm frequency among identical twins. If so, I told you, you could have stopped reading this post at point 1.