The Secret Sway of Hormones


omo sapiens is one of the few species on earth that care if they’re seen having sex. The impala is unconcerned. The dingo roundly flaunts it. A masturbating chimpan­zee will stare straight at you. To any creature other than you and I and 6 billion other privacy-needing H. sapiens, sex is like peeling a mango or scratching your ear. It’s just something you do sometimes. This morning, sitting on an observation platform high above a playground-sized rhesus enclosure at the Yerkes National Primate Research Center with researcher Kim Wallen, I have watched a half-dozen monkey couplings, and I’m fairly certain that the situation has caused me more discomfort than it has them.

Wallen and I are here not because of the differences between the sex lives of humans and monkeys, but because of some surprising similarities. Wallen, whom we met in chapter 3, is a professor of behavioral neuroendocrinology at Emory University He studies sexual desire and the hor­mones that influence it. Wallen’s Female Sexuality Project involves testing different combinations of hormones to see how they effect libido. The hormones are being given to rhesus monkeys, not because monkeys complain about dampened libidos, but because women do—and because monkeys and women have the same hormones, and these hormones affect them in many of the same sorts of ways.

An independent woman may believe herself to be sub­ject to no one and nothing beyond her own volition. And much of the time she is. But there are times, times when certain hormones peak and fertility is at its maximum, that she may find herself behaving in ways that later puzzle her. Hormones can act as the invisible puppet strings behind the discomfiting one-night stand, the shameless flirta­tion with the bellboy, the unexpected and regrettable kiss between friends. Your genes want you to get pregnant, and hormones are their magic wand.

A dozen studies bear this out. One team of researchers, Stanislaw and Rice, asked 4,000 women to write down the first day within their menstrual cycle when they noticed an increase in sexual desire; the dates peaked at mid-cycle. Women who are part of couples will initiate sex more often at mid-cycle than during the rest of the month—provided they’re using a reliable birth-control method (and don’t wish to become pregnant); if they’re not, then they typically avoid mid-cycle sex. Women also masturbate significantly more often around ovulation than at other times. Take the hormones away, as menopause does, and these mid-cycle spikes in libido level out.

Monkeys offer an unadulterated demonstration of the power of hormones, as the females are not concerned about pregnancy or what their friends will think. Mon­keys don’t wait until the weekend, or until they’ve lost two more pounds, or until their roommate is out of town. Here in the rhesus compound, it is much more the case that hor­mones determine who has sex and when. Their hold over a female animal can be impressive. When they are not close to ovulation, female rhesus monkeys have little to do with males. For the most part, they avoid them. But when they are fertile, they pursue the males constantly, initiating about 80 percent of the sexual encounters they will have.

Right now, in the enclosure below us, the puppet mas­ter has control of a shy, skinny monkey whom the research­ers have named Page. Page is in heat for the first time. Since we got here, she’s been hanging around Keystone, the troupe’s boastful, burly alpha male. Alpha males are easy to spot. They are larger by half than the females, and their tails stand in the air like a lion tamer’s whip. Lest you for­get that Keystone is the alpha male, he does a conspicuous display every ten minutes or so, to remind you of it. He may bounce straight up and down, basketball-like, five or six times. Or he may leap up onto the chain-link fence and shake it by the lapels. It is the rhesus monkey equivalent of karate or doing donuts in the parking lot.

Kim Wallen is not an alpha male sort of guy. He has been married for twenty-five years. He says “crapola” when he misses a freeway exit. Today he is dressed in chinos and hiking shoes. His shirt is quietly checkered, and his tie has two small spots on it from the fish soup he ate for lunch. Perhaps because of the photo of him on the Emory Web site, in which he is leaning against a large tree trunk, a woman once wrote to him, “You look like a man who’d like to go for a walk.”

A hawk circles above us, and the monkeys hoot and clamor. It’s the sound that the crowd makes when George Clooney arrives on the red carpet outside the Oscars. We watch as Page gradually, subtly, moves closer to Keystone.

“They do what looks like a random walk, but each time they stop, they’re a little closer. It’s like the teenage dance, where you’re interested in a guy and you kind of hang around in the area, waiting to go get punch until he goes up to get punch.” Wallen says he and his colleagues some­times entertain themselves by going to bars and trying to guess who’ll end up with whom at the end of the evening, based on their behavior early in the evening. “It’s exactly like following these animals.” Page is now four or five feet from Keystone, picking up a rock, as though that rock were the reason she crossed the enclosure just now.

Why the coyness and hesitation? In Page’s case, it has to do with her low rank and the risks that go along with it. If she’s too obvious in her solicitations, she stands a chance of being thwacked by a higher-ranking female. Furthermore, adult male rhesus monkeys—if you’re a female rhesus— are big and intimidating. “Imagine it,” says Wallen. “You’re this little teeny female, you’ve done nothing with the adult males for all of your preadolescent period, and all of a sud­den you wake up one day and say, You know, this guy is really attractive.’ ”

Page just sat down a foot away from Keystone, at the top of a climbing structure. In the world of monkeys, this counts as a come-on. Primate researchers call it “initiat­ing proximity.” I’m actually feeling nervous for her. Wallen leans forward in his chair. “If you watch, sometimes you can actually see their hands shake.”

A higher-ranked female named Gawk just lunged at Page. “If Page didn’t have strong enough motivation”—i. e., the push provided by hormones—“it—sex—would just never happen,” Wallen says. If you take away the compli­cated, anxiety-provoking social structure that exists in the Yerkes compound (or in the wild), hormones cease to mat­ter as much. A lone male and a lone female monkey placed in an enclosure together will get down to business in no time.[85] There’s no risk involved.

Among women too, socially risky sex tends to happen when the hormones hit their peak. In a study by M. A. Bei­lis and R. R. Baker, the sex that cheating women were hav­ing with their lovers closely mirrored their monthly cycle, peaking on the day of maximum fertility. But the sex these women were having with their husbands was randomly dis­tributed throughout the month. The women’s hormones, it appears, were providing the extra impetus needed to take on the risk of getting caught.

“Look!” I shout to Wallen, who has turned away to speak with a graduate student who has joined us, inputting behavior observations on a laptop. Keystone has stepped up onto a female’s back legs as though they were stilts. “They’re doing it!”

“That’s not Page,” says Wallen. “That’s Tequila.” Tequila is the beta female. As a high-ranked female, she gets mounted out of courtesy. Meanwhile, Page is parked at the feeding ledge, seemingly consoling herself with Monkey

Chow. One eye remains on the Keystone scenario. As soon as Tequila moves away, Page sets out again. She stops near Keystone. She slides her hand toward him.

In the social lexicon of the rhesus, this is a subtle come-on, or “present” (short for “presentation”).[86] Less subtle overtures include moving one’s tail out of the way, touching the male, or gently slapping the ground in front of him. Part of the reason it took primatologists—who were, in pre-Jane Goodall days, all men—so long to acknowledge the female rhesus monkey’s role in initiating sex was that the solicitations were so, well, forward. “There was a very strong predisposition not to be looking for that,” Wallen says. The pioneering primatologist C. R. Carpenter first documented the hand slap as a female sex solicitation in the 1940s, but his papers were ignored for years.



look down at my notepad and when I look up again, I catch Keystone and Page in the act. Despite the protracted buildup, it’s not the least bit arousing to watch. Monkeys have sex the way we pump a keg or fluff a pillow: a brief series of repetitive actions undertaken with no discernible passion or emotion, and not a terrific amount of interest.

Over the next few minutes, Keystone mounts Page repeatedly, but always seems to lose interest after a few desultory thrusts. Wallen explains that rhesus monkeys are “multimount, multi-intromission ejaculators.” He’ll be on her and off her five or ten times before he finishes up. “There goes the mount. That’s an intromission.

Three pelvic thrusts. Now the dismount.” If Yerkes ever loses its funding, Wallen could find work as an Olympics commentator.

This kind of furtive, piecemeal copulation might have evolved as a way of passing on your genes while at the same time avoiding a possibly life-threatening fight with another male. The sneakier you are about it, the less attention you attract and the less jealousy you provoke, and the longer you live.

The other strategy is to be a speedy ejaculator: in and done before the other males notice what you’re up to. Male chimps are tops at this. A research paper on the origins of premature ejaculation (PE) states that chimpanzees ejacu­late within an average of seven seconds after they mount a female.[87] The author speculates that it is perhaps because of this that chimpanzees are known for a lack of aggression among males during mating season. It’s hard to get irritable over a liaison that takes less time to finish than a banana.

This author lists the human male’s average time lapse between penetration and orgasm as two minutes—placing him midway between the chimp and the orangutan (eleven minutes). U. K. sex physiologist Roy Levin puts two min­utes at the fringes of normal; his figure for an average male’s thrusting time is two to five minutes (or, if you pre­fer, 100 to 500 thrusts). In the latest papers on premature ejaculation, two minutes falls a scant half minute outside the category “probable premature ejaculation.”[88] Does our author have a personal premature-ejaculation ax to grind? “If premature ejaculation was normal and advantageous in the past,… why is it labeled dysfunction today? …” he writes tellingly. “If rapid ejaculation is normal, then premature ejaculation by itself should not be of clinical concern unless it is extreme, such as occurring before intromission.” The author advocates placing more emphasis on “the tender touch, the passionate caress, the gentle rub, the titillating probe”—all of the things men do better than orangutans— rather than making men miserable by asking them to try to expand their ejaculatory latency. A point well taken, but still and all, sympathies to the Mrs.


exual desire is a state not unlike hunger. You may find yourself getting up for a snack long before you’re aware of a physical sensation. If you are a single woman midway through her cycle, you may find yourself on a barstool or a set of front steps you swore you’d never climb again. In the words of young Page (via the mouthpiece of Kim Wallen), “I don’t know what I’m doing here, but here I am.”

Wallen is leaning back in his chair, with one foot on a rusted railing. “I have no concept at all of what’s attrac­tive in a rhesus,” he is saying. “But I have seen males mate with females that struck me as incredibly tmattractive.” And vice versa. This is what primate sex hormones do: “They make individuals perceive other individuals as more attrac­tive than they’d normally perceive them.” Hormones are nature’s three bottles of beer.

But not if you’re on the Pill. In humans, a hormone – based contraceptive levels out the monthly peaks and troughs of one’s natural hormone levels—and, in conse­quence, those of libido. The Pill supplies a steady daily dose of hormones, enough that your body stops supply­ing its own unsteady, cyclically fluctuating dose. While the Pill’s estrogen levels are high enough to prevent ovulation, they are lower than a natural mid-cycle peak. Says urologist and sex advice author Jennifer Berman, “The Pill basically puts you into a kind of menopausal state.”

The Pill contains estrogen and progesterone, but it also affects testosterone. And it is testosterone, more than any other hormone, that influences a woman’s libido. What the Pill does, specifically, is raise levels of sex-hormone­binding globulin (SHBG), a protein in the blood that binds itself to testosterone, taking the hormone out of commis­sion. And going off the Pill might not restore libido. In a 2006 study, urologist Irwin Goldstein looked at women’s levels of SHBG and of their free (unbound) testosterone while they were on the Pill and after they’d gone off it. Their SHBG didn’t decrease after they stopped taking the Pill, and their testosterone levels—and, presumably, their libido—didn’t recover.

Why hasn’t low libido been listed as a side effect for oral contraceptives? “The FDA doesn’t consider behavior and in particular sexual behavior to be something they’re con­cerned about,” says Wallen. And why don’t doctors men­tion it to women before they pick up the prescription pad? In part because not that many women on the Pill complain about low libido. One in four is the statistic I’ve heard. For many women, the freedom from worrying about preg­nancy cancels out any mid-cycle dip in libido; they’re hav­ing more sex then, not less. The Pill doesn’t make women enjoy sex less, it doesn’t change their responsiveness; it just mutes their drive. A lot of them don’t even notice, and for some, it’s a price worth paying.

Menopause is a natural, more exaggerated version of being on the Pill. Estrogen and testosterone levels fall, tak­ing libido along with them. As a solution to flagging sexual desire in postmenopausal women, Procter & Gamble, in 2004, came up with a testosterone patch, called Intrinsa. When the FDA asked for more safety data, the company dropped their plans—no doubt skittish after the sudden crash-and-burn of postmenopausal hormone-replacement therapy. But in July 2007, the EMEA, Europe’s version of the FDA, went ahead and approved Intrinsa for women with hypoactive sexual desire disorder (low libido). Ameri­cans who want to try it need look no further than the clos­est Internet pharmacy.

The testosterone patch was the subject of vigorous debate at the 2007 meeting of the International Society for the Study of Women’s Sexual Health (held, to no one’s amusement but my own, at Disney World). An endocri­nologist’s pro-patch presentation was met with vocal con­cerns that researchers and their pharmaceutical company sponsors were, as one attendee put it, “making a normal midlife phenomenon into a disease.” ■


f only rhesus monkeys could read some of the human studies they’ve inspired. What would they make, for instance, of sixty-two married American women, for three months running, smearing synthesized rhesus monkey “sex pheromones” onto their chests before getting into bed? The smears did not, it turned out, inspire the husbands to have sex with their wives more often than usual. They did not inspire anything at all, except possibly the idiom “There’s something I need to get off my chest.”

Why did sixty-two American women do this? The short answer is that the researchers paid them. (One dollar a day. This was 1977.) The long answer is that monkey-observing scientists used to believe that the reason rhesus monkeys have more sex around the time the females ovulate is not that the female is under the sway of hormones that push her to make a move, but rather that the female has pher­omones—chemical triggers of behavior—that prompt the males to make a move. (Sex pheromones are commonplace in other neighborhoods of the animal kingdom—among insects, for instance, and rodents and swine—but olfactory sex triggers for primates were until this point unknown.)

The rickety notion of rhesus—and, by implication, human—sex pheromones can be traced to a rhesus mon­key research colony in the U. K. and to the behavioral neuroendocrinologist who observed it. In 1971, Richard Michael claimed to have pinpointed compounds in the vaginal secretions of his females that, when sniffed, caused the male monkeys to initiate sex. (But not very many of them. Critics point out that just two males accounted for 50 percent of the data.) Michael called the purported rhe­sus pheromones “copulins,”[89] a word I cannot write with­out picturing a race of small, randy beings taken aboard the starship Enterprise.

Other endocrinologists had doubts about Michael’s claim. D. A. Goldfoot and three colleagues at the Wiscon­sin Regional Primate Research Center made “lavages”—a pretty French word for the liquid they got from washing out the vaginas of rhesus monkeys in heat—and smeared the substance onto the back ends of neutered (i. e., non­hormone-producing) females. The expectation was that if copulins were for real, the males would try to mate with the lavage-anointed, neutered females. The males did not.

Michael’s sex-pheromone work got tremendous media coverage nonetheless, which is unfortunate, as it sent our understanding of female hormones and female sexual behavior way off down the wrong boulevard. It implied that when it came to sex, the female primate was a passive receptacle with no drive or interest of her own.

However, I cannot hold this against Dr. Michael, for his work inspired a highly diverting period of scien­tific inquiry. In 1975, for example, a team of researchers from the Monell Chemical Senses Center in Philadel­phia launched an investigation of changes in the “pleas­antness” of women’s vaginal odors across their monthly cycle. Seventy-eight subjects were asked to sniff tampons that four women had worn during the various phases of their cycle. (For obvious reasons, the women were asked not to eat onions, garlic, or asparagus for the duration of the study. Less obviously, the women were discouraged from eating broccoli, brussels sprouts, cabbage, chili, curry, kale, sauerkraut, and pineapple.) The supposition was that the odors might be more appealing during a woman’s ovulatory phase than at other times during her cycle. And they were: Subjects judged them slightly more pleasant and less intense than at other times. However, the authors reported, the data did not go so far as to “support the notion. . . that vaginal secretion odors are particularly pleasant to human males.”[90]

There was one other nominee for human sex-phero­mone status: A compound called androstenone was found to exist in men’s underarm sweat. Androstenone had long been known as a potent swine sex pheromone; when a pig in heat sniffs it, she becomes receptive to being mounted by a boar. Hence its presence in male bodily secretions sent endocrinologists into frenzies of speculation. Its actual effect on women proved unclear—though not for want of trying. For years, psychologists and endocrinologists took to sneaking around in public spaces spraying furniture and bathroom stall doors with cans of Boarmate, a synthetic, aerosolized version of androstenone.

Occasionally, the studies seemed to turn up an effect. M. D. Kirk-Smith and a colleague at the University of Birmingham in the U. K. sprayed Boarmate on what had been determined to be an unpopular seat among women visitors to a dentist’s waiting room. The aim was to see if more women would now be attracted to this chair. The seat’s popularity was secretly observed by receptionists. The Boarmate appeared to work its charms on the women, who sat in the chair significantly more often than they had before Kirk-Smith and the can of Boarmate hit the scene.

What does the dentist chair project prove about women and men and their interactions with each other? Nothing, says George Preti, of the Monell Chemical Senses Center, who was dismissive of the study and critical of its method­ology The bottom line is that men’s armpit secretions are unlikely to serve as an attractant to any species other than the research psychologist.

Despite the washy evidence that androstenone has an effect on human sexual behavior, it wasn’t long before someone patented an androstenone-based human sex attractant. Winnifred Cutler used to work with George Preti. The two parted ways when she began placing ads in the backs of men’s magazines for Athena Pheromone 10X (“Raise the Octane of Your Aftershave”). Cutler published a study stating that men who added 10X to their cologne were having significantly more dates and more sex than a control group. She concluded that her product had made the men more sexually attractive. Preti, in turn, claimed that Cutler had failed to demonstrate solid evidence that this was so. And to this day, no amount of 10X can bring the two together at industry gatherings.

I have a better suggestion for Cutler’s customers. Stop wearing cologne. Women don’t find it attractive. If you don’t believe me, here is a quote from a press release from the Smell and Taste Treatment and Research Foundation in Chicago: “Men’s colognes actually reduced vaginal blood flow.” Foundation director A1 Hirsch hooked women up to a vaginal photoplethysmograph and had them wear surgical masks scented with ten different aromas or com­binations of aromas. (To be sure the women weren’t just getting aroused by dressing up in surgical masks, Hirsch put unscented masks onto a control group.) In addition to the smell of cologne, the women were turned off by the scent of cherry and of “charcoal barbeque meat.” At the top of the women’s turn-on list was, mysteriously, a mix­ture of cucumber and Good ’n’ Plenty candy It was said to increase vaginal blood flow by 13 percent.[91]

Though the existence of human pheromones remains open to debate, sexuality does seem to play a role in how men and women respond to the scent of each other’s hor­mones. Researcher Ivanka Savic of Stockholm’s Karolinska Institute asked straight women and gay men to sniff a par­ticular hormonal component of male sweat. As they did so, their hypothalamus lit up on a PET brain scan, suggesting a sexual response rather than just an olfactory one. The same kind of brain response showed up when Savic had straight men—and, in a second study, lesbians—sniff an estrogen­like compound found in women’s urine. Savic emphasized that the sweat and urine compounds did not—as would a true pheromone—prompt any changes in behavior, except, possibly, refraining from signing up for future Ivanka Savic studies.

Monkey Do