A Natural History of Love

by Diane Ackerman

  Later in life, oxytocin seems to play an equally important role in romantic love, as a hormone that encourages cuddling between lovers and increases pleasure during lovemaking. The hormone stimulates the smooth muscles and sensitizes the nerves, and snowballs during sexual arousal—the more intense the arousal, the more oxytocin is produced. As arousal builds, oxytocin is thought to cause the nerves in the genitals to fire spontaneously, bringing on orgasm. Unlike other hormones, oxytocin arousal can be generated both by physical and emotional cues—a certain look, voice, or gesture is enough—and can become conditioned to one’s personal love history. The lover’s smell or touch may trigger the production of oxytocin. So might a richly woven and redolent sexual fantasy. Women are more responsive to oxytocin’s emotional effects, probably because of the important role it plays in mothering. Indeed, women who have gone through natural childbirth sometimes report that they felt an orgasmic sense of pleasure during delivery. Some nonorgasmic women have found it easier to achieve orgasm after they’ve been through childbirth; the secretion of oxytocin during delivery and nursing melts their sexual blockade. This hormonal outpouring may help explain why women more than men prefer to continue embracing after sex. A woman may yearn to feel close and connected, tightly coiled around the mainspring of the man’s heart. In evolutionary terms, she hopes the man will be staying around for a while, long enough to protect her and the child he just fathered.

  Men’s oxytocin levels quintuple during orgasm. But a Stanford University study showed that women have even higher levels of oxytocin than men do during sex, and that it takes more oxytocin for a woman to achieve orgasm. Drenched in this spa of the chemical, women are able to have more multiple orgasms than men, as well as full body orgasms. Mothers have told me that during their baby’s first year or so they were surprised to find themselves “in love” with it, “turned on” by it, involved with it in “the best romance ever.” Because the same hormone controls a woman’s pleasure during orgasm, childbirth, cuddling, and nursing her baby, it makes perfect sense that she should feel this way. The brain may have an excess of gray matter, but in some things it’s economical. It likes to reuse convenient pathways and chemicals for many purposes. Why plow fresh paths through the snow of existence when old paths already lead part of the way there? New fathers feel gratified by their babies, too, and their oxytocin levels rise, but not as high.

  How about cuddling among other animals? At the National Institute of Mental Health, neuroscientists Thomas R. Insel and Lawrence E. Shapiro have been studying the romantic lives of mountain voles, promiscuous wild rodents that live alone in remote burrows until it’s time to mate, which they do often and indiscriminately. Mother voles leave their pups soon after birth; father voles don’t see their pups at all; and when a researcher removes a pup from its nest it doesn’t cry for its mother or seem particularly stressed. They have nothing like what we might call a sense of family. What the researchers have found is that mountain voles have fewer brain receptors for oxytocin than their more affectionate and family-oriented relatives, the prairie voles. Despite this, but just as one might predict, the oxytocin levels of the mountain voles do climb steeply in mothers right after birth, while they’re nursing their pups. Such a study makes one wonder about the complex role that oxytocin plays in human relationships. Are oxytocin levels lower in people characterized as “loners,” in abusing parents, in children suffering from the solitary nightmare of autism?

  THE INFATUATION CHEMICAL

  First, a small correction of something we take for granted. The mind is not located in the brain alone. The mind travels the body on an endless caravan of hormones and enzymes. An army of neuropeptides carries messages between the brain and the immune system. When things happen to the body—like pain, trauma, or illness—they affect the brain, which is a part of the body. When things happen in the brain—like shock, thought, or feeling—they affect the heart, the digestive system, and all the rest of the body. Thought and feeling are not separate. Mental health and physical health are not separate. We are one organism. Sometimes hunger pangs override morality. Sometimes our senses wantonly crave novelty, for no other reason than that it feels good. Sometimes a man does indeed think with his dick. Because we prize reason and are confused about our biology, we refer to our body’s cravings and demands as our “baser” motives, instincts, or drives. So it is craven to yearn for sex, but noble to yearn for music, for example. Depraved to devote hours to finding sex, but admirable to devote hours to searching out beautiful music. Perverted to spend an afternoon fantasizing and masturbating repeatedly, but wholesome to spend the same afternoon enraptured by music. When love becomes obsession, the whole body hears the trumpet blast, the call to arms.

  “The meeting of two personalities is like the contact of two chemical substances,” Carl Jung wrote, “if there is any reaction, both are transformed.” When two people find each other attractive, their bodies quiver with a gush of PEA (phenylethylamine), a molecule that speeds up the flow of information between nerve cells. An amphetaminelike chemical, PEA whips the brain into a frenzy of excitement, which is why lovers feel euphoric, rejuvenated, optimistic, and energized, happy to sit up talking all night or making love for hours on end. Because “speed” is addictive, even the body’s naturally made speed, some people become what Michael Liebowitz and Donald Klein of the New York State Psychiatric Institute refer to as “attraction junkies,” needing a romantic relationship to feel excited by life. The craving catapults them from high to low in an exhilarating, exhausting cycle of thrill and depression. Driven by a chemical hunger, they choose unsuitable partners, or quickly misconstrue a potential partner’s feelings. Sliding down the slippery chute of their longing, they fall head over heels into a sea of all-consuming, passionate love. Soon the relationship crumbles, or they find themselves rejected. In either case, tortured by lovesick despair, they plummet into a savage depression, which they try to cure by falling in love again. Liebowitz and Klein think that this roller coaster is fueled by a chemical imbalance in the brain, a craving for PEA. When they gave some attraction junkies MAO inhibitors—antidepressants that work by disabling certain enzymes that can subdue PEA and other neurotransmitters— they were amazed to find how quickly the therapy worked. No longer craving PEA, the patients were able to choose partners more calmly and realistically. Other studies with humans seem to confirm these findings. Researchers have also found that injecting mice, rhesus monkeys, and other animals with PEA produces noises of pleasure, courting behavior, and addiction (they keep pressing a lever to get more PEA). All this strongly suggests that when we fall in love the brain drenches itself in PEA, a chemical that makes us feel pleasure, rampant excitement, and well-being. A sweet fix, love.

  The body uses PEA for more than infatuation. The same chemical soars in thrill-seeking of any kind, because it keeps one alert, confident, and ready to try something new. That may help explain a fascinating phenomenon: people are more likely to fall in love when they’re in danger. Wartime romances are legendary. I am part of a “baby boom” produced by such an event. Love thrives especially well in exotic locales. When the senses are heightened because of stress, novelty, or fear, it’s much easier to become a mystic or feel ecstasy or fall in love. Danger makes one receptive to romance. Danger is an aphrodisiac. To test this, researchers asked single men to cross a suspension bridge. The bridge was safe, but frightening. Some men met women on the bridge. Other men encountered the same women—but not on the bridge—in a safer setting such as a campus or an office.

  The men who met the women on the trembling bridge were much more likely to ask them out on dates.

  THE ATTACHMENT CHEMICAL

  While the chemical sleigh ride of infatuation carries one at a fast clip over uneven terrain, lives become blended, people mate and genes mix, and babies are born. Then the infatuation subsides and a new group of chemicals takes over, the morphinelike opiates of the mind, which calm and reassure. The sweet blistering rage of infatuati
on gives way to a narcotic peacefulness, a sense of security and belonging. Being in love is a state of chaotic equilibrium. Its rewards of intimacy, warmth, empathy, dependability, and shared experiences trigger the production of that mental comfort food, the endorphins. The feeling is less steep than falling in love, but it’s steadier and more addictive. The longer two people have been married, the more likely it is they’ll stay married. And couples who have three or more children tend to be lifelong spouses. Stability, friendship, familiarity, and affection are rewards the body clings to. As much as we love being happily unsettled, not to mention dizzied by infatuation, such a state is stressful. On the other hand, it also feels magnificent to rest, to be free of anxiety or fretting, and to enjoy one’s life with a devoted companion who is as comfortable as a childhood playmate, as predictable if at times irksome as a sibling, as attentive as a parent, and also affectionate and loving: a longtime spouse. This is a tonic that is hard to give up, even if the relationship isn’t perfect, and one is tempted by rejuvenating affairs. Shared events, including shared stresses and crises, are rivets that draw couples closer together. Soon they are fastened by so many it becomes difficult to pull free. It takes a vast amount of courage to leap off a slowly moving ship and grab a lifebuoy drifting past, not knowing exactly where it’s headed or if it will keep one afloat. As the “other women” embroiled with long-married men discover, the men are unlikely to divorce, no matter how mundane their marriages, what they may promise, or how passionately in love they genuinely feel.

  THE CHEMISTRY OF DIVORCE

  “Philandering,” we call it, “fooling around,” “hanky-panky,” “skirt chasing,” “man chasing,” or something equally picturesque. Monogamy and adultery are both hallmarks of being human. Anthropologist Helen Fisher proposes a chemical basis for adultery, what she calls “The Four-Year Itch.” Studying the United Nations survey of marriage and divorce around the world, she noticed that divorce usually occurs early in a marriage, during the couple’s first reproductive and parenting years. Also, that this peak time for divorce coincides with the period in which infatuation normally ends, and a couple has to decide if they’re going to call it quits or stay together as companions. Some couples do stay together and have other children, but even more don’t. “The human animal,” she concludes, “seems built to court, to fall in love, and to marry one person at a time; then, at the height of our reproductive years, often with a single child, we divorce; then, a few years later, we remarry once again.”

  Our chemistry makes it easy to follow that plan, and painful to avoid it. After the seductive fireworks of first attraction, which may last a few weeks or a few years, the body gets bored with easy ecstasy. The nerves no longer quiver with excitement. Nothing new has been happening for ages, why bother to rouse oneself? Love is exhausting. Too much of anything feels overwhelming, even too much thrill. Then the attachment chemicals roll in their thick cozy carpets of marital serenity. Might as well relax and enjoy the calm and security, some feel. Separated even for a short while, the partners crave the cradle of the other’s embrace. Is it a chemical craving? Possibly so, a hunger for the soothing endorphins that flow when they’re together. It is a deep, sweet river, just right for dangling one’s feet in while the world waits.

  Other people grow restless and search for novelty. They can’t stand the tedium of constancy. Eventually the ghost of old age stalks them. They are becoming their parents. Elsewhere, life is storied with new horizons, and new flanks. Everyone else seems to be enjoying a feast of sensual delicacies, and they want to smother themselves in a sauce of sensations. So they begin illicit affairs or divorce proceedings, or both.

  One way or another the genes survive, the species prevails. Couples who stay together raise more kids to adulthood. When couples part, they almost always marry again and raise at least one child. Even when the chemical cycle falters and breaks, it picks itself up and starts again. Both systems work, so both reward the players. As Oscar Wilde once said, “The chains of marriage are heavy and it takes two to carry them—sometimes three.”

  APHRODISIACS

  In the second half of the nineteenth century, French doctors wrestled with a strange dietary mystery. Soldiers stationed in North Africa, after dining on frogs’ legs, developed severe cases of priapism, a prolonged and painful érection of the penis. In 1861, Dr. M. Vezien, making his rounds in a field hospital, was impressed by the “érections douloureuses et prolongées” with which several legionnaires returned his salute, and he questioned them about their menu. Could these men have been poisoned? Frogs’ legs are a popular French delicacy, and the soldiers had eaten a local variety of frog that lived in a nearby swamp. When Dr. Vezien collected some of the frogs and dissected their stomachs, he found remnants of meloid beetles. In 1893, another military doctor in North Africa reported a similar case: same steely erections, same frogs, same frog guts filled with same beetles.

  Cornell biologists have solved the mystery of the erect penises and the aphrodisiac frogs. Meloid beetles contain cantharidin, a urinary-tract irritant otherwise known as “Spanish fly.” Many men—most notably the Marquis de Sade—have dosed themselves with it to boost their virility, and dosed ladies with it to win their consent.

  When a man’s potency flags, he’s willing to try almost anything as a pick-me-up. Oysters, caviar, powdered rhinoceros tusk, cocks’ combs, figs, eggs, “Love Potion Number Nine,” ambergris, bull’s blood (drawn from the testes), camel’s milk, phallic-shaped fruits, or such “lascivious”* vegetables as asparagus. These remedies sometimes work, either because the user thinks they will or because they provide a vitamin or trace mineral the person lacks. People don’t feel very sexy if they’re unhealthy. For example, oysters contain zinc, and men with diets low in zinc tend to have a low sperm count. That doesn’t mean that a plate of oysters will make a man feel sexy … unless the texture of the oysters excites his imagination, suggesting a woman’s nether petals, as well it might. In the grand opera of the imagination, everyday foods may suddenly become succulent and magical. If he is dining with his ladylove, and the oysters remind him of a bicycle trip they took along the windswept dunes of Cape Cod, and an afternoon when they made love on a secluded beach, their skin lightly scoured by the sand, the surf loud as a freight train, and the briny smell of the ocean rich in their nostrils, then simply eating the oysters will touch off a sensual circus.

  Ginseng, a nutrient plant native to Korea, Russia, and China, is reputed to be a tonic for the nervous system in general and thus a boon to potency. A spicy bowl of bird’s nest soup, also said to be an erection special, is made from the nests that sea swifts build in caverns along the coast. The nests provide much phosphorus and other minerals. Asparagus is a rich source of potassium, phosphorus, and calcium—all of which are essential for energy—and it stimulates the urinary tract and kidneys, which may be why seventeenth-century herbalist Nicholas Culpepper advised that asparagus “stirreth up bodily lust in man and woman.” The Japanese claim that unagi, raw eel, makes a fine aphrodisiac, and there are thousands of restaurants in Japan that specialize in eel. The dish is often served with some form of pickle, the most expensive and prized coming from a phallic-shaped plum.

  Men have often presented women with flowers, chocolates, perfumes, music, and other pleasurable treats to put them in a romantic mood. “Awaken her senses first” seems to be the unstated motto of suitors. In any case, flowers are the plants’ sex organs, and they evoke the sex-drenched, bud-breaking free-for-all of spring and summer. Chocolate contains mild central nervous system stimulants, as well as an amphetaminelike chemical the body produces naturally when we’re in love. Montezuma drank fifty cups of chocolate a day, to boost his virility before he visited his harem of six hundred women.*

  Most perfumes contain the essences of flowers mixed with secretions from wild animals (musk, civet, ambergris, and the like), or laboratory versions of them. Smelling a randy pig might not sound sexy, but we are sometimes remarkably simple abou
t what turns us on. Seeing or hearing or smelling other animals having sex can be inspiration enough. Truffles contain a chemical similar to the male pig sex hormone, which is why hot-to-trot sows eagerly dig them up. But the chemical is also similar enough to a human male hormone that its mustiness appeals to human diners, too. It has even been used in various popular perfumes.

  Although the celibate Capuchine monks invented cappuccino, that exquisite frothy typhoon of whipped hot milk and espresso, coffee drinkers are statistically more sexually active than other people. But then, they’re more active about everything. Tried and true, alcohol works well at the outset, by relaxing inhibitions, but then it depresses the nervous system just when it should be jubilant. It was Shakespeare (in Macbeth) who warned that alcohol “provokes the desire, but takes away the performance.” The ancient Egyptians claimed radishes were aphrodisiacs. Ovid swore by onions, perhaps because of Martial’s epigram: “If your wife is old and your member is exhausted, eat onions in plenty.” But a more popular Roman aphrodisiac was a sauce made from rotting fish entrails, and prettied up under the name of liquamen. Travelers to Pompeii bought it at a famous factory owned by Umbricus Agathopus. They relied on live snails cooked in peppery liquamen sauce; mushrooms coated in a honey-and-liquamen sauce; roasted venison eaten with a caraway, honey, vinegar, and liquamen sauce on the side; soft-boiled eggs stewed in a pine kernel, honey, and liquamen sauce; wild boar basted with liquamen sauce; and, for variety, a sort of shish kebab of truffles dipped in liquamen sauce.