Sex at Dawn

While her subjects were being buffeted by this onslaught of varied eroticism, they had a keypad where they could indicate how turned on they felt. In addition, their genitals were wired up to Plethysmographs. Isn’t that illegal? No, a plethysmograph isn’t a torture device (or a dinosaur, for that matter). It measures blood flow to the genitals, a surefire indicator that the body is getting ready for love. Think of it as an erotic lie detector.

What did Chivers find? Gay or straight, the men were predictable. The things that turned them on were what you’d expect. The straight guys responded to anything involving naked women, but were left cold when only men were on display. The gay guys were similarly consistent, though at 180 degrees. And both straight and gay men indicated with the keypad what their genital blood flow was saying. As it turns out, men can think with both heads at once, as long as both are thinking the same thing.

The female subjects, on the other hand, were the very picture of inscrutability. Regardless of sexual orientation, most of them had the plethysmograph’s needle twitching over just about everything they saw. Whether they were watching men with men, women with women, the guy on the beach, the woman in the gym, or bonobos in the zoo, their genital blood was pumping. But unlike the men, many of the women reported (via the keypad) that they weren’t turned on. As Daniel Bergner reported on the study in The New York Times, “With the women . mind and genitals seemed scarcely to belong to the same person.”⁴ Watching both the lesbians and the gay male couple, the straight women’s vaginal blood flow indicated more arousal than they confessed on the keypad. Watching good old-fashioned vanilla heterosexual couplings, everything flipped and they claimed more arousal than their bodies indicated. Straight or gay, the women reported almost no response to the hot bonobo-on-bonobo action, though again, their bodily reactions suggested they kinda liked it.

This disconnect between what these women experienced on a physical level and what they consciously registered is precisely what the theory of differential erotic plasticity predicts. It could well be that the price of women’s greater erotic flexibility is more difficulty in knowing—and, depending on what cultural restrictions may be involved, in accepting—what they’re feeling. This is worth keeping in mind when considering why so many women report lack of

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interest in sex or diffaculties in reaching orgasm.