Bonk by Mary Roach

“Nature has favored domestic animals over womankind,” she lamented in her paper, pointing out that the clitorises of these animals were “located right on the border of the genital orifice.” Given that the average horse or cow liaison is over in a matter of seconds, these creatures sorely need a clitoral leg up. It’s just as well Bonaparte never investigated the private bits of the domestic sow, whose clitoris sits inside its vagina.
     
    i f the distance is less than the width of your thumb, you are likely to come.” This catchy anatomical ditty was penned not by Marie Bonaparte, but by Kim Wallen, an Emory University professor of behavioral neuroendocrinology. Wallen spends most of his time studying sex hormones at the Emory-based Yerkes National Primate Research Center on the outskirts of Atlanta, but he has of late been researching the physiology of intercourse. Wallen, who has a starring role in chapter 14, was the person who first told me about the princess and her clitoral travails. He was intrigued by Bonaparte’s findings, but he did not, at first, put much stock in them, mainly because the science of statistics in 1924 was relatively primitive. Then he ran her numbers himself. The vaginal-clitoral distances, he said, turned out to perfectly predict which women would have orgasms in intercourse and which wouldn’t. The cutoff point, as Bonaparte had noted, lay at around an inch—the width of a typical thumb. I asked him if he was going to trademark his “rule of thumb.”
    “Yes,” he deadpanned. “And I’m going to start selling a little custom-made ruler.”
    Bonaparte includes only 43 of the 243 subjects’ measurements in her paper, so Wallen’s data were limited to those. Nonetheless, the data are so consistent that 43 turns out to be more than enough to say that there is, as he puts it, a very powerful, statistically reliable relationship. “Certainly strong enough to say there’s something here that’s worth looking at.” Wallen plans to do a larger study himself, as soon as he has time.
    A more recent study of genital variations among fifty women confirmed the range of distances Bonaparte found: from a half inch to almost two inches, with an average at around an inch. This study, by U.K. gynecologist Jillian Lloyd and colleagues, had nothing to do with orgasm. Lloyd sought to document the truly remarkable degree of variation in the size and shapes of women’s genital features. * The hope was to reassure those who worry that their clitoris, say, is abnormally large or their pubic hair too rangy. Pornography, Lloyd points out, exposes us to idealized, highly selective images, making women needlessly self-conscious (and labia-reduction surgeons rich).
    Wallen, like Masters and Johnson, thinks it’s possible that a majority of the so-called vaginal orgasms being had during intercourse are in reality clitoral orgasms. But unlike Masters and Johnson, he doesn’t suggest that most women are having them easily. He believes, like Bonaparte, that the women having them—the paraclitoridiennes of the world—are an anatomically distinct group whose sexual response is different from that of the majority of women. And that maybe these women are “where the whole notion of the vaginal orgasm originally came from.”
    I offered to be a statistic in Wallen’s new study. He sent me detailed instructions on how to do the measuring. It’s not as simple as it sounds, because Bonaparte’s measurements—and thus Wallen’s too—were from the clitoris to the urethra (where urine exits the body), rather than from clitoris to vagina. (The urethra is dependably close to the clitoris and makes a more precise measuring point.) A clitoris is easy to find, but urethras are sometimes hidden inside the opening to the vagina, and often hard to see. I emailed Wallen twice with questions.
    “It is interesting,” he wrote back, “that you could reach this stage of life and never really have any call to know how