Bonk: The Curious Coupling of Science and Sex

by Mary Roach

The body’s limiting factors seem to get shut off.* The organism is driven toward nature’s singular goal—conception, the passing on of one’s genes—and anything that stands in the way is pushed into the background. Sensory distractions become imperceptible: noises go unheeded and peripheral vision all but disappears—a fact some prostitutes use to their advantage, working with “creepers” who emerge from the shadows when the action heats up and go through the john’s pockets as easily as if he were unconscious.

The most dramatic example

of this biological priority shift is a sexually mediated disregard for pain and physical discomfort. Whatever ails you pretty much stops ailing you during really hot sex. Fevers and muscle aches, Kinsey cl...

Heart rate and blood pressure, it turns out, are more reliable indicators of orgasm than they are of deceit.)

The clitoris hides at a certain point in the proceedings. In the stage of arousal just before orgasm, the visible portion of the clitoris retracts under its tiny foreskin. It disappears from view, potentially creating great confusion and consternation on the part of the person doing the stimulating. Masters points out that the clitoris, at this point, is likely to be too sensitive for direct contact anyway.

(Subjects were either on their backs or on all fours, doggy-style.) So what, then, was bringing these women to their peak? “Penile traction on the labia minora,” said Masters and Johnson: Penis going into vagina pulls on

labia, which in turn pull on clitoris.

“the biggest detriment for effective female response was male control

of thrusting pattern.” In other words, a phallus is a welcomed addition to female pleasure, as long as the woman has some say about it—its speed, its angle, its depth, its outfit.*

In Alfred Kinsey’s sample of 8,000 women, 20 percent reported occasionally making some kind of “vaginal insertions” when they masturbated—though usually in addition to doing something directly clitoral. It was Kinsey’s opinion that many of these women penetrated themselves because their husbands liked to watch them, or because they didn’t know any better. It’s mo...

zone, or whatever you wish to call it), and that they weren’t simply thrusting straight-on, like a pen...

i f the distance is less than the width of your thumb, you are likely to come.”

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.

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.

Bonaparte also discovered a correlation between a woman’s height and how close together her vulval features are. Shorter women tend to have shorter

spans.

Based on a small, anecdotal survey that he’d probably prefer I not mention, Wallen has also been finding that women with small breasts seem more likely to have shorter distances.

The stereotypical ideal female—Barbie tall with Barbie big breasts—is the one least likely to respond to a manly hammering.

Levin ran a small investigation that focused on the erotic sensitivity of the female urethra. More specifically, his interest was in the toenail-sized patch of tissue that surrounds the outlet of the urethra: the periurethral glans. In men, this glans, which lies at the tip of the penis, is exquisitely erogenous. Levin has observed that when women have intercourse, the female glans, as he calls it, is repeatedly pulled partway inside the vagina—as much as half of it typically disappears into the crevasse with each thrust. Perhaps women who have orgasms during intercourse, he reasoned, are women who are

more erotically sensitive in this spot. (Though you’d think that, here again, proximity might play a role; i.e., the closer the glans is to the vagina, the more gets pulled inside.)

Jessamyn Neuhaus, in an article about marriage manuals in the Journal of the History of Sexuality, credits the birth of the birth-control movement for this change. Having spent the past century shackled to reproduction, sex suddenly emerged as

a recreational pastime. Orgasm—particularly women’s—became a prerequisite for good health and matrimonial harmony, and dozens of authors, medical and not, chimed in with tips on how to achieve it.

The key, explained Dickinson, was to find a position in which the man’s pubic bone pressed against the woman’s clitoris and/or moved it to and fro.

“Women who routinely have orgasm in intercourse without explicit clitoral stimulation all say that it makes little difference what the guy does, as long as he doesn’t come too soon,” Wallen said in an email. Meaning, it’s the women’s own movement that matters most.

the last portion of a man’s ejaculate contains a natural spermicide—not intended to kill his own soldiers, obviously, but to annihilate the seed of any who come after him.

Erections are all about blood. Blood is the backbone of a stiff penis.

The blood resides in a pair of cylindrical chambers—the corpora cavernosa—which lie side by side like a diver’s tanks. The chambers are filled with smooth-muscle erectile tissue, full of thousands of tiny hollow spaces, like a sponge. When the smooth-muscle tissue relaxes—which it does at the behest of an enzyme activated when the brain

perceives a sexual stimulus—it expands. (Smooth muscle, unlike the striated muscles of your arms and legs, is operated by the autonomic nervous system; this is why men can’t simply will themselves erect—or unerect.) The relaxation of the erectile tissue allows blood to rush in and fill out the spongy hollows. Drugs like Viagra enhance the erection process by knocking out a substance nicknamed PDE5, which inhibits smooth-muscle relaxation. They inhibit the inhibitor. (Thus, they’re called PDE5 inhibitors.)

The blood that has filled the two erection chambers* must be trapped there, otherwise the erection wilts. This is tricky, as the chambers are equipped with drainage veins along their surface. What keeps the blood from leaking out via these veins? The miracle of passive venous occlusion. (Stay with me here.) These drainage veins lie outside the erection chambers but inside the stiff outer membrane (called the tunica) that protects the erectile tissue. When the chambers expand with blood, they slam up against the tunica—which also expands, but not as much—and this pressure squeezes shut the veins caught in

between. If all goes well, the blood stays trapped until a postorgasm chemical messenger tells the smooth-muscle tissue to stop relaxing.

When a man is impotent, very often it’s because the erectile tissue isn’t expanding as vigorously as it needs to squeeze shut the veins, and some of the blood...

The bitter irony here is that regularly spilling one’s seed serves a valuable biological function. Sex physiologist Roy Levin explained to me that sperm which sit around the factory a week or more start to develop abnormalities: missing heads, extra heads, shriveled heads, tapered and bent heads. All of which render them less effective at head-banging their way into an egg. Levin speculates that that’s why

men masturbate so much: It’s an evolutionary strategy. “If I keep tossing myself off, I get fresh sperm being made.” Thereby upping the likelihood of impregnating someone and passing on your genes.

Though if conception is the goal, you don’t want the sperm to be too fresh. Daily masturbation would deplete the number of sperm per ejaculate. Got to give the pinheads time to build up their ranks. To produce an ejaculate with optimum potential...

Dr. Foreman explains that one pair of pelvic floor muscles runs along the sides of the penis like guy wires and helps hold it erect. Another pelvic floor muscle encircles the penis and, when tightened, puts pressure on the dorsal vein and helps trap blood inside the penis. Toning these muscles should, in theory, help men have firmer, longer-lasting erections.

A man can have an orgasm—or even multiple orgasms*—without ejaculation, and he can have an orgasm and/or ejaculation without an erection.

Maravilla has found that, on average, women’s clitorises hold twice as much blood while they are watching porn than when they are watching, say, footage of a Space Shuttle launch.

FSAD is the ladies’ edition of ED (erectile dysfunction). It is distinct from FOD (female orgasmic disorder) and HSDD (hypoactive sexual desire disorder, or low libido).* Confusingly, there is also female sexual dysfunction, or FSD, but this is simply the catch-all term for anyone who has one—or a combination—of these conditions. Lack of desire (HSDD) is the most common of women’s sexual complaints,

Male and female fetuses both begin life with something closer to a clitoris. The male’s expands into a penis, while the female’s remains more or less as is.

Even in their adult forms, the two organs have much in common. The clitoris, like the penis, ends in a sensitive, nerve-dense, pleasure-yielding bulb of tissue called a glans. Like the penis, the clitoris has a shaft, and that shaft contains a pair of expandable chambers called corpora cavernosa. It also has a prepuce, or foreskin, just like the penis does, and if you draw it back you may, just as with the penis, discover a wee cache of smegma.

And yes, a clitoris expands when its owner is aroused—though not as quickly or extravagantly as does a penis. Masters and Johnson filmed dozens upon dozens of clitoral erections: Responses to vibrators, to fingertips, to “stimulative literature,” to intercourse.

Along these same lines, exercise has been shown to improve a woman’s ability to get aroused. Which makes sense: Exercise makes the body more efficient at pumping blood.

Suction will pull more blood and make the clitoris more sensitive. That’s what suction does.”

the muscle tone, strength, and straining involved in orgasm are similar to that of “jumping, gymnastics, tennis, football….”

Sipski defines orgasm as a reflex of the autonomic nervous system that can be either facilitated or inhibited by cerebral input (thoughts and feelings).

The electronics term for circuitry mix-ups is crosstalk: a signal traveling along one circuit strays from its appointed route and creates an unexpected effect along a neighboring circuit. Crosstalk explains the faint voices from someone else’s conversation

in the background of a telephone call. Crosstalk in the human nervous system explains not only the man who enjoyed his toilette, but also why heart attack pain is sometimes felt in the arm, and why the sensations of childbirth have been known to include orgasmic feelings or, rarely, an urge to defecate. Orgasms from nursing (or nipple foreplay) are another example of crosstalk. The same group of neurons in the brain receive sensory input both from the nipples and the genitals. They’re the feel-good neurons: the ones involved in the secretion of oxytocin, the “joy hormone.” (Oxytocin is involved in both orgasm and the milk-letdown reflex in nursing mothers.)

When a woman is turned on by something or someone, her brain sends a signal to open up more of the capillaries in her womanly recesses. This ups the amount of

blood in her vaginal walls, and some of the clear portion of it seeps through the capillaries and coats the vagina. Hello, lubrication.

A series of studies by Meredith Chivers and colleagues at the Centre for Addiction and Mental Health in Toronto showed that men are more discriminating than women when it comes to how they respond to pornographic images. Women, both gay