Cupid's Comeuppance

To capture the mystery, caprice and force of romantic love, the ancients conjured Cupid, a mischievous immortal in whose thrall we are wholly powerless. Science provides a different view. By exploring human nature, we discover that being smitten—at first or forever—is a function of invisible forces, but there's little that's capricious about them. The real arrows in Cupid's quiver distill personal history and serendipity into a cache of chemicals that bathes the brain, compelling us to act in ways that are mistaken for fate or folly. Understanding the hidden power of biology to shape our most cherished relationships may banish Cupid to the Sistine ceiling forever.

MAKING LOVE'S FIRST BLUSH LINGER ON

Who has not felt that they are the happiest, the luckiest and the only human to fall so completely in love? The physical and emotional fanfare that heralds love's arrival is hard to forget—and more difficult still to sustain. If the romance goes well, the heart-stopping phone calls you once anticipated with fervor become a familiar ring; that furtively glimpsed visage may be the first and last face you see each day. Enduring love inevitably progresses to this stage: an attachment that is deeper, but far less exciting, than initial infatuation.

Indeed, the experience of love may best be viewed as a biological drive that comprises lust, romantic love and attachment. These three states are experientially different, but share the goal of successful reproduction. Lust gets us on the hunt for potential mates, and romantic love narrows our focus and energy to just one person, while attachment encourages us to stick with this partner long enough to raise children.

These three systems are expertly choreographed at the neurochemical level, each with attendant neurohormones, contends Helen Fisher, a research anthropologist at Rutgers University in New Brunswick, New Jersey. It's the neurochemical dopamine in particular that allows us to maintain romantic love's unique, intoxicating properties, even as we tread water in the tranquil sea of long-term attachment.

Dopamine and norepinephrine levels surge when a person is confronted by the unknown. In the initial phase of romantic love, they engender such exhilaration that we lose the desire to eat or sleep. The French refer to this as le coup de foudre ("lightning bolt"). Less romantic Anglophones call it lovesickness. Fisher, for her part, equates romantic love with addiction. She argues that whether the motivator is cocaine or Cindy in apartment 4B, elevated levels of dopamine and norepinephrine electrify the reward system in the brain. "Romantic love is an urge, a craving, a homeostatic imbalance that drives you to pursue a particular partner, and to [experience] emotions like elation and hope, or despair and rage," explains Fisher.

The awe of dopamine eventually subsides, followed by love's rear guard, vasopressin and oxytocin, hormones that lead to long-lasting attachment. Researchers hypothesize that these "cuddle chemicals," released during sex, facilitate the bond needed to raise children. Warm and fuzzy though they make us feel, these hormones can't match dopamine's edgy high. Oxytocin, in particular, may subdue levels of dopamine and norepinephrine.

It may be wise to invoke the thrill and power of dopamine by embracing new adventures, since novelty prompts the brain to pump out this chemical. "Novelty drives up dopamine levels and probably lowers the threshold for your ability to feel romantic love," Fisher explains. In other words, new and varied stimuli can be sufficiently arousing to recapture what was initially so exciting about your mate. "When you do novel things, you're not ingesting any substance; you're just creating an internal reaction—just as romantic love creates an internal reaction," says Fisher.

Indeed, several studies have shown that couples who share exciting experiences report more relationship satisfaction, as well as more romance, than do couples with more mundane habits.

Novelty may be so critical to romantic love that it helps account for the success of arranged marriages. Many Westerners roll their eyes at the practice, trampling as it does on our notions of courtship and the soul mate. But Fisher suggests that an arranged union offers suspense about one's partner-to-be, the fulfillment of a long-anticipated promise and the thrill of wedding pageantry—experiences that can drive up dopamine levels to such a degree that romantic love may thrive.

Novelty-generating forces are available to most relationships. Prime among them are humor (never underestimate the power of the unexpected quip) and sex. Sex elevates testosterone levels, which in turn rev up dopamine, allowing partners to recapture the thrill of romantic love, if only temporarily.

The simplest way to shake up your relationship is well documented by the likes of Homer or Tennessee Williams: enforced separation and knock-down, drag-out fights. Arguments trigger a rush of adrenaline, which kicks in during risky, dangerous or new situations. This may explain the high-voltage couple who dramatically splits only to reconcile with still more gusto. Separation from a beloved moves dopamine and norepinephrine production into high gear by activating goal-driven pathways associated with these neurotransmitters. "When a reward is delayed, these brain circuits sustain their activity, which is probably what gives you the feeling of frustration attraction—wanting the person more when barriers are increased," explains Fisher.

There's just one catch in Fisher's prescription for novelty: A couple's conception of behavior that is comfortable or challenging must be in sync for fresh experiences to have the desired effect. Unfortunately, not everyone is in sensory agreement.

SENSATIONALLY OUT OF STEP

Let's face it: We live in a fast-paced world. Gone is the serenity of Victorian idylls that still infuse our vision of romance, complete with slow-motion Sundays in the park and picnics by pristine lakes.

While the recesses of our brain reserved for romance marinate in some melange of fiction and hope, our nerve endings snap to attention against a shortage of time. Communication is often curt as couples juggle bills, office deadlines and babysitters who don't show.

This is the nature of life in the 21st century. Elegant and gracious it is not.

Against this backdrop, relationships struggle to survive once the exhilaration of courtship gives way to the routines of partnership. And couples struggle to achieve a congruence that is generally out of the reach of awareness—but that exerts a powerful centripetal pull nonetheless.

One factor that may prove unifying—or divisive—is the degree to which two nervous systems are naturally inclined to pursue novel and stimulating experiences. We are not talking about conjoint bungee-jumping, rather about the openness each person has toward change and his or her appreciation of variety and intensity of experience, as well as each one's strong positive emotional reactivity to new situations.

People normally differ in the degree to which they seek stimulation. But the most enduring couples, it turns out, are those whose natural levels of sensation seeking, whether high, low or in between, are very closely aligned.

People who strongly possess the capacity for sensation seeking are tuned in to an internal thrum and choose environments that augment internal sensations. They are usually very social, seeing others as a source of stimulation, although they answer more to their own needs than to social conventions. And the company they prefer is interesting, going on exotic.

The degree of sensation seeking is usually well-correlated between happily married partners. In studies at the University of Delaware, psychologist Marvin Zuckerman has found a large discrepancy in the sensation-seeking scores of husbands and wives undergoing marital therapy. Usually, he reports, it is the low-level sensation seeker who drags in the high-level sensation seeker for marital counseling.

The best combination is two people low in sensation seeking. "They're happy with each other and don't become habituated to each other," explains Zuckerman. "Two high [-level] sensation seekers are OK for a while, but even though their partner might be exciting, they are looking for variety everywhere." Still, the worst combination is high-low, because they just don't understand each other's interests.

A person's inherent need for sensation is not necessarily obvious in the early stages of a relationship, when love itself is a novelty and carries its own thrills. And you don't have to be a high-level sensation seeker to enjoy sex, says Zuckerman.

"It's when the sex becomes routine that problems occur. Initially there can be a great attraction between a high [-level] and a low [-level]. And only later may they realize how fundamentally different they are."

As with all behavior, there is some flexibility built into the system. Up to a point, some low-levels can learn to do things they might not ordinarily choose. And high-levels can modify their sensation needs. But even if they reach agreement on how to spend their time together, and what to do on vacation, the tempo is always going to be somewhat unrewarding for one of them. The activities that most satisfy, the kinds of people they like, their interest in socializing at all—the balance points between routine and spontaneity, between stability and variety—are bound to differ and can drive a wedge between them.

The high-sensation seekers and the lows also have different brain responses to activity. At the highest end of sensation seeking stand the risk takers of the world—people who are impelled to explore unknown territory, experiment with drugs or engage in dangerous activities. "High-sensation seekers don't need an explanation. Lows want an explanation about why people do such things," Zuckerman reports.

The highs know. They get an all-around rush, probably brought to them by a surge in the neurotransmitter dopamine. Among sensation seekers, Zuckerman has found, dopamine levels are low and very reactive to stimulation. He believes that high-sensation seekers have reduced dopamine levels because they have low levels of monoamine oxidase (MAO), a brain-active enzyme that regulates dopamine and other neurotransmitters. Serotonin levels are also low among sensation seekers. Low serotonin levels are associated with impulsive behavior. And so the combination of tendencies might be due to the balance between serotonin and dopamine in the brain.

In general, women have higher MAO levels than men, while sensation seeking tends to be greater among men than among women. Nevertheless, happy husbands and wives can be found—and by extension, ought to be looking for each other—at roughly the same spot on the sensation-seeking scale. "Most personality traits do not show what's called 'assortative mating,'" that is, they do not gravitate toward their own level in a partner. But sensation seeking does. And that, says Zuckerman, is a clear sign of its biological importance.

WHY LOVE MAKES SCENTS

Dripping candles, perfume-doused letters, red roses—so much of romance leads us by the nose. It turns out that one of the most subtle but important forces steering love is the body's own unadulterated scent. If a couple's odor-prints don't match, they won't make sense together.

Scent is a driving force at all stages of a relationship, argues Rachel Herz, visiting assistant professor of psychology at Brown University. She has found that scent is the second most important criterion for women (after a pleasant disposition). Women are more interested in scent than in appearance, voice or muscle tone. While men also rank scent highly, Herz argues that women are the more aromatically susceptible sex. Because women bear the brunt of reproduction, they have evolved to regard smell as a more significant signal.

People know which cologne drives them crazy, but their preference for one person's smell over another's is at the mercy of biological processes that generally operate below the level of conscious awareness.

The source of each person's one-of-a-kind odor is, in fact, his or her unique immune system. The segment of our DNA called the major histocompatibility complex (MHC) controls proteins involved in immunity—and in producing our own singular smell. Immunity is inherited from both parents, and because the human species is best protected by the broadest array of disease resistance, we are designed to mate with a partner whose MHC profile differs from our own. As such, studies suggest that we like the scent of people with immune systems unlike ours. Couples with similar immune systems have a higher risk of spontaneous miscarriages and have more trouble conceiving.

A classic set of experiments reveals the degree to which MHC-driven scents silently engineer mate preferences. Claus Wedekind of the University of Bern in Switzerland asked women to sniff and select cotton clothes that were worn by various men. The women not only favored the shirts of men whose MHC profiles differed from theirs but also said these aromas reminded them of current or ex-lovers—proof that MHC profiles influenced their romantic choices in the past. T-shirts worn by men who had similar immune systems to the women conjured up fathers or brothers instead.

Women taking oral contraceptives, however, were dangerously misled in partner preference: They found the dad-and-brother-like smells most attractive. The pill tricks a woman's body into acting as if she's pregnant. One theory holds that the olfactory system knows it is advantageous for a woman to be around kin when she is in such a vulnerable state.

Perhaps, Herz suggests, the widespread use of the pill is a factor in our sky-high divorce rates: "Marriage counselors say that a [top] complaint from women who want to end a relationship is, 'I can't stand his smell.'"

A few years into marriage, a woman may stop using birth control only to find herself less interested in her mate without knowing why. Herz now advises women who use the pill to try alternate means of birth control before settling down with a partner.

But a change in scent perception will not necessarily make a woman turn up her nose for good. Once two people are emotionally attached, they are disposed to see—and smell—each other in a positive light.