Brains Do It: Lust, Attraction, and Attachment

“What t’is to love?” Shakespeare asked. Thousands of answers have been offered—but surprisingly few by biologists, including brain scientists. Perhaps at some level scientists share the poet’s conceit that love is ineffable, a human fifth dimension beyond reason’s ken. While scientists regard other complex emotional states such as depression, anxiety, or fear as complex, but not unfathomable, love is relegated to the poets and songsters.

Neglecting the biology of the emotions that direct mating and reproduction, emotions that in our species are sometimes called “love,” has had tragic consequences. Certainly such love can be a joyous state, but it is also capable of producing deeply disturbing, even dangerous results. At least 25 percent of homicides in the United States involve spouses, sexual partners, or sexual rivals. Each year, some one million American women are followed and harassed by rejected lovers; 370,000 men are stalked by former partners; and approximately 1.8 million wives in the United States are beaten by their husbands. In fact, male sexual jealousy is the foremost cause of wife battering in cultures worldwide. Husbands, although to a lesser degree, are physically abused by wives. Men and women in societies everywhere can experience clinical depression when a love relationship fails; and psychologists say that a significant percentage of those who commit suicide do so because they have been rejected by a beloved.

Love is a powerful force; the vast majority of Americans marry. But the divorce rate in the United States is expected to reach 67 percent in the next decade. Currently, some 80 percent of divorced men and 72 percent of divorced women remarry; but 54 percent and 61 percent, respectively, divorce again. High divorce and remarriage rates are seen in many other cultures, as well. It is time to investigate the biology of this bittersweet experience we call love.

Three Emotion Systems that Complicate Human Life

I believe that three primary, distinct, but interrelated emotion systems in the brain mediate mating, reproduction, and the rearing of young: lust, attraction, and attachment. Each emotion system is correlated with a specific neurobiology in the brain; each is associated with a different repertoire of behavior; and each evolved to direct a specific aspect of reproduction in birds and mammals.

THE SEX DRIVE (libido or lust) is characterized by the craving for sexual gratification and associated primarily with the hormones (the estrogens and the androgens). The sex drive evolved to motivate individuals to seek sexual union with any appropriate partner.

THE ATTRACTION SYSTEM (in humans termed “passionate love,” “obsessive love,” or “infatuation”) is characterized by increased energy and the focusing of attention on a preferred mating partner. In humans, attraction is also associated with feelings of exhilaration, intrusive thinking about the beloved, and the craving for emotional union. Attraction, I hypothesize, is associated in the brain primarily with high levels of the neurotransmitters dopamine and norepinephrine and with low levels of serotonin. This emotion system evolved chiefly to enable males and females to distinguish among potential mating partners, conserve their mating energy, prefer genetically superior individuals, and pursue these individuals until insemination had been completed.

THE ATTACHMENT SYSTEM (termed “companionate love” in humans) is characterized in birds and mammals by behavior that may include defense of a mutual territory, mutual nest building, mutual feeding and grooming, separation anxiety, and shared parental chores. In humans, attachment is also characterized by feelings of calm, security, social comfort, and emotional union. Attachment is associated in the brain primarily with the neuropeptides oxytocin and vasopressin. This emotion system evolved to motivate individuals to sustain their affiliations long enough to complete the parental duties of their species.

For each system, the neural circuits can be expected to vary from one species to the next, among individuals within a species, and over the life of an individual. The three emotion systems also act in concert with one another and with other bodily systems. For example, a person may begin a sexual liaison merely for sexual pleasure, then become romantically involved with this sexual partner. He can become deeply attached to this partner, too, and these enhanced feelings of attachment can be explained biologically. After orgasm, levels of vasopressin rise in men; levels of oxytocin rise in women. These hormones are known to cause attachment, and probably contribute to the feelings of closeness after sexual intercourse.

The three emotion systems can act independently, as well. Individuals in approximately 90 percent of bird species form seasonal or lifelong pair bonds, becoming attached and rearing their offspring together. Yet “a lot of birds are having a bit on the side,” reports Jeffrey Black of Cambridge University.¹ In fact, individuals in only 10 percent of the 180 or so species of socially monogamous songbirds are sexually faithful to their mating partners; the rest engage in “extra-pair” copulations.

Likewise, men and women can express deep attachment for a long-term spouse or mate at the same time they express attraction for someone else, and also while they feel the sex drive in reaction to situations unrelated to either partner. We are physiologically capable of “loving” more than one person at a time.

The independence of these emotion systems may have evolved among our ancestors to enable males and females to take advantage of several mating strategies simultaneously. With this brain architecture, they could form a pair bond with one partner and practice clandestine adultery too, thereby taking advantage of rare “extra” mating opportunities. They could also practice polygamy if the opportunity arose. But for modern humans, these distinct brain circuits have enormously complicated life, contributing to today’s worldwide patterns of adultery and divorce; the high incidence of sexual jealousy, stalking, and spouse battering; and the prevalence of homicide, suicide, and clinical depression associated with romantic rejection.

What is the biology of these emotion systems? Why did they evolve in humans? To what extent do they control our lives? How should we use this information in the practice of medicine and the law? I will consider lust, attraction, and attachment separately, and focus my attention on attraction, the least understood of these fundamental emotion systems, the one we have come to call “romantic love.”

Lust: “The Interolerable Neural Itch”

W. H. Auden called the sex drive “an intolerable neural itch.” Scientists have long regarded that itch as a distinct emotion system that is innate and common to all birds and mammals—lodged in the avian and mammalian brain. Moreover, they have long understood at least the basic neuroanatomy and physiology of the libido, agreeing that it is predominantly associated with the androgens in both men and women. The estrogens also play substantial roles in the sex drive in many mammals, but only a secondary role in humans.

The biological relationship between the sex drive and the attraction system has not been well defined in most mammals; but in the small rodents called prairie voles, studies have shown that the two systems regularly interact. When a female prairie vole receives a drop of male urine on her upper lip, the neurotransmitter norepinephrine is released in specific areas of the olfactory bulb in her brain. This helps to stimulate the release of estrogen and contributes to triggering sexual behavior. In the prairie vole, attraction is a brief, spontaneous, chemically induced, excitatory reaction that initiates sexual desire, sexual physiology, and sexual behavior.

Lust and attraction do not always go hand in hand in people. When middle-aged men and women are injected with testosterone, their sex drive increases, but they do not fall in love. Moreover, men and women can express sexual desire toward those for whom they feel no obsessive attraction or deep attachment.

“Lust is the oldest lion of them all,” says an Italian proverb. The factors that trigger the libido vary from one individual and one species to the next, but the sensation itself, which is associated with a specific constellation of neural correlates, evolved to initiate the mating process. This emotion system, however, probably also contributes to many cases of date rape and other forms of inappropriate human sexual conduct.

Attraction: The “Delirium of Eros”

Robert Lowell called love “this whirlwind, this delirium of Eros.” Romantic love, obsessive love, passionate love, infatuation: Call it what you will, almost all men and women around the world have known its ecstasy and anguish.

In 1991, anthropologists surveyed accounts of 166 societies and found evidence of romantic love in 147 of them. (In the other 19, researchers had simply failed to examine this aspect of daily living). Everywhere they looked, they found evidence of this passion. People sang love songs or composed romantic verse. They performed love magic, carried love charms, or brewed love potions. Some eloped. Some committed suicide or homicide because of unrequited love. In many societies, myths and fables portrayed romantic entanglements. Thus, anthropologists believe that romantic attraction is a universal or near-universal human experience. I will go even further: I think romantic love, attraction, is common to all mammals and birds.

Naturalists have implicitly acknowledged the existence of this emotion system for over a century. In 1871, Darwin wrote of a female mallard duck who became attracted to a pintail duck, a bird of a different species. Citing the report of a colleague, Darwin wrote, “It was evidently a case of love at first sight, for she swam around the newcomer caressingly… From that hour she forgot her old partner.” The animal literature is filled with such descriptions. Dogs, horses, gorillas, canaries: Males and females of many species assiduously avoid mating with some individuals and resolutely focus their attention on others.

Darwin further discussed attraction when he wrote about the evolution of the “secondary sexual characteristics,” all of the gaudy, cumbersome accoutrements that creatures flaunt, such as the peacock’s unwieldy tail feathers. He reasoned that birds and mammals evolved these bodily decorations for one of two reasons: to impress or fight members of the same sex to win breeding opportunities or to attract members of the opposite sex. Yet he failed to note that these physical traits must trigger some type of physiological attraction response in the viewer.

Today many scientists call this attraction “favoritism,” “selective proceptivity,” “sexual preference,” “sexual choice,” or “mate choice.” As yet, however, they have not examined the biological process by which the viewer comes to prefer and choose a mate. I theorize that birds and mammals have evolved a specific “attraction circuit” in the brain that becomes active when an individual sees, hears, smells, or touches an appropriate mating partner—a neural circuit that creates a condition humans have come to call romantic love.

My hypothesis is that feelings of romantic attraction are associated with high levels of the neurotransmitters dopamine and norepinephrine and with low levels of serotonin. I arrived at this thesis after culling 13 psycho-physiological characteristics of romantic love from the past 25 years of psychological literature, then matching these traits, where possible, with known properties of dopamine, norepinephrine, and serotonin. Several of the 13 traits can be so matched with what is now known about brain chemistry. These traits include the experience of novelty, intrusive thoughts, focused attention, increased energy, and powerful feelings of elation.

THE EXPERIENCE OF NOVELTY. When we fall in love, we first begin to feel that our beloved is novel, unique. The love object takes on special meaning. As one person reported: “My whole world had been transformed. It had a new center, and that center was Marilyn.” This phenomenon is coupled with the inability to feel romantic passion for more than one person at a time. Kabir, a 15th century poet of India, wrote of this: “The lane of love is narrow. There is room only for one.”

Increased concentrations of dopamine in the brain are associated with exposure to a novel environment. Increased levels of dopamine are also associated with heightened attention, motivation, and goal-directed behaviors. These parallels suggest that levels of dopamine are rising in the brain as a lover focuses on a beloved.

INTRUSIVE THOUGHTS. We begin to think about our beloved obsessively, engaging in what is known as “intrusive thinking.” As a line from an 8th century Japanese poem reads, “My longing has no time when it ceases.” Many people report that they think about their “love object” over 85 percent of their waking hours.

Serotonin re-uptake inhibitors (which increase active levels of the chemical messenger serotonin) are currently the agents of choice in treating most forms of obsessive-compulsive disorder (OCD). As intrusive thinking is a form of obsessive behavior, I have speculated for some time that low levels of serotonin are responsible for the intrusive thinking of romantic passion. Now, neuroscientist Donatella Marazziti of Pisa University and her colleagues have confirmed that low levels of serotonin are indeed associated with romantic attraction. These researchers studied 20 students who reported that they had recently fallen in love, 20 patients with unmedicated OCD, and 20 control subjects. Blood platelets from those who said they were in love and those with unmedicated OCD showed a significantly lower density of a serotonin transporter protein, a protein involved in the travel of serotonin between nerve cells.² In short, as one begins to fall in love, levels of serotonin decrease.

FOCUSED ATTENTION. When possessed by love, we tend to focus our attention on the positive qualities of the beloved, and to overlook or falsely appraise negative traits. Infatuated men and women also focus on events, objects, songs, letters, and other things that they have come to associate with the beloved. An unpublished survey I designed and administered to 420 American and 430 Japanese men and women illustrates this point: 72 percent of men and 84 percent of women remembered trivial things that their beloved said; 82 percent of men and 90 percent of women said they replayed these precious moments as they mused.

As we saw in discussing the experience of novelty, increased levels of central dopamine are associated with focused attention. Moreover, we know that the neurotransmitter norepinephrine is associated with increased memory for new stimuli. Increased levels of norepinephrine in the brain have also been associated with “imprinting.” Imprinting is a term from the study of animal behavior that was originally used to define the instinctive behavior of infant geese as they begin to focus their attention on their mothers, following them everywhere. The focused attention of the infatuated man or woman appears much like imprinting on the beloved—an indication that increased concentrations of norepinephrine are involved.

INCREASED ENERGY AND POWERFUL FEELINGS. Possessed by love, we aquire a great deal of energy, and we are at the mercy of powerful feelings: exhilaration, euphoria, buoyancy, spirituality, sleeplessness, loss of appetite, awkwardness, trembling, pallor, flushing, stammering, butterflies in the stomach, sweaty palms, weak knees, a pounding heart, and accelerated breathing— even panic or fear in the presence of our beloved. We are also subject to abrupt mood swings. If the relationship suffers a setback, we may fall into listlessness, brooding, and feelings of despair. As Freud said, “We are never so defenseless against suffering as when we love.”

Increased concentrations of dopamine and norepinephrine in the brain have been shown to be associated with excessive energy, euphoria, loss of appetite, increased mental activity, hyperactivity, and decreased need for sleep—suggesting that these neurotransmitters contribute to the labile feelings associated with romantic attraction.

More Traits of Romantic Love

The remaining nine psycho-physiological traits that are commonly associated with romantic love do not as yet appear to have any direct correlation with dopamine, norepinephrine, or serotonin. Still, they may be associated with these neurochemicals in as yet undefined ways.

1. Lovers report feelings of emotional dependency on the relationship, coupled with changeable emotions, including hope, apprehension, possessiveness, jealousy, preoccupation with the beloved, vulnerability, fear of rejection, and separation anxiety. So lovers monitor their relationships. As Robert Graves put it, “listening for a knock; waiting for a sign.”
2. Those who are infatuated long for emotional reciprocity and emotional union with the beloved.
3. They feel a powerful sense of empathy toward the beloved, including a feeling of responsibility for the loved one and a willingness to sacrifice for him or her.
4. The love-possessed tend to reorder their daily priorities to become available to the beloved, and strive to make a favorable impression, by changing their clothing, mannerisms, habits, even their values.
5. Lovers may also experience what psychologists call the “Romeo and Juliet Effect” —an intensification of passionate feelings due to adversity.
6. Most people smitten by romantic love experience sexual desire for the beloved, coupled with the drive for sexual exclusivity. In fact, both men and women become ardently jealous if they suspect infidelity in a romantic partner. This desire for sexual exclusivity may be the most important evolutionary function of this emotion system: it drives partners to exclude other suitors, thereby insuring that courtship is not interrupted until insemination has been completed.
7. Yet, for those who are “in love,” the craving for emotional union often takes precedence over the desire for sexual union with the beloved. Sixty-four percent of both sexes in the survey I conducted disagreed with the statement, “Sex is the most important part of my relationship with _____”
8. The love-possessed also commonly report that their passion is involuntary and uncontrollable. “Love is like a fever,” wrote the French novelist Stendahl; “It comes and goes quite independently of the will.”
9. Romantic attraction is usually impermanent, ephemeral. Unless a physical or social barrier inhibits partners from seeing one another regularly, this passion eventually wanes. Scientists recently tried to establish the duration of infatuation. When Marazziti retested serotonin levels in the 20 infatuated men and women some 12 to 18 months after the lovers had started their romances, these levels had risen—becoming indistinguishable from those of the control group. On this basis, the researchers surmised that passionate romantic love generally lasts six to 18 months.

Chemistry and Culture

Passionate romantic love comes in graded forms, of course, from elation to despair, from calm to anxiety, depending on whether one’s love is reciprocated or unrequited. So I would expect that these gradations of feeling are associated with different levels of dopamine, norepinephrine, and serotonin, as well as other less primary neurochemicals.

To try to pinpoint the brain circuitry associated with passionate romantic love, my colleagues Gregory V. Simpson, Lucy L. Brown, and Seppho Ahlfors, neuroscientists at the Albert Einstein College of Medicine at Yeshiva University, and I placed four infatuated individuals in a functional Magnetic Resonance Imaging (fMRI) machine and showed them photographs of their love object, as well as photographs of another individual, as a control. We have not yet conclusively analyzed these data, but I anticipate that areas of the ventromedial prefrontal cortex, the amygdala, sectors of the anterior cingulate region, the nucleus accubens, the hypothalmus, and regions of the brain stem will be involved. We are continuing this investigation of romantic attraction with Arthur P. Aron, a psychologist at the State University of New York at Stony Brook, and psychology graduate student, Debra Mashek, also at SUNY, Stony Brook.

Attraction, as an emotion system, evolved to perform essential functions in the mating process. It enables individuals to select between potential partners, conserve and focus their mating energy, and maintain this focus until insemination occurs. But for humans, whom we fall in love with is an entirely different matter, one largely shaped by cultural forces.

For example, timing is essential; men and women fall in love when they are ready. Also, most men and women are attracted to someone who is somewhat mysterious, unfamiliar. This may have evolved as a mechanism to counteract inbreeding. But the primary factors that ignite the romantic blaze are our childhood experiences. Psychologist John Money of Johns Hopkins University theorizes that, somewhere between the ages of five and eight, individuals begin to develop a “love map,” an unconscious list of traits they will later look for in a mate. For example, some people want a partner who will debate with them, or educate them, or mask aspects of their personality they do not admire in themselves. This mental template is complex and unique; Money believes it solidifies at puberty.

So when you fall in love, with whom you fall in love, where you fall in love, what you find attractive in a partner, how you court your beloved, even whether or not you regard this passion as divine or destructive, varies from one society and one individual to the next. But once you find that special person, the actual physical feeling you have as you experience this passion is chemically induced. It evolved along with the rest of your body.

Romantic love can be joyous, but it also fuels human jealousy and possessiveness. As an emotion system, attraction almost certainly contributes to modern patterns of stalking, crimes of passion, and the incidence of suicide and clinical depression associated with romantic rejection.

Attachment: from Prairie Voles to People

Psychologists have recognized attachment as a specific emotion since John Bowlby began to record attachment behaviors in humans and other mammals in the 1950s. In social mammals, these behaviors include maintaining proximity and displaying separation anxiety when apart. In pair-bonding species, the male often defends the territory, and partners feed and groom one another and share parental chores. Among humans, men and women also report feelings of closeness, security, peace, and social comfort with a long-term partner, as well as mild euphoria when in contact and separation anxiety when apart for unusual periods.

Several neuropeptides are associated with male/female pair bonding, group bonding, and mother/infant bonding. The work of Sue Carter (a behavioral endocrinologist at the University of Maryland), Tom Insel (a neuroscientist at the Yerkes Regional Primate Research Center in Atlanta), and their colleagues has shown, however, that the primary hormones involved in the production of attachment behaviors in monogamous prairie voles are vasopressin and oxytocin. Insel and his collaborators have recently studied a gene associated with the receptor binding vasopressin. When this gene is transferred from monogamous prairie voles to non-monogamous laboratory mice, and these mice are injected with vasopressin, the once-unaffectionate mice express increased affiliative behaviors.³

Because the gene family that includes vasopressin and oxytocin is found in all mammals and birds, and because humans share variations of these basic bodily substances, it seems probable that vasopressin and oxytocin are also involved in feelings of attachment in men and women. And there is no question that attachment is a distinct neural system. Spouses in arranged marriages and long marriages frequently maintain a visible attachment to one another, express feelings of attachment, and display mutual parental duties—without displaying or reporting feelings of attraction or sexual desire for this mate.

Marital or other long-term attachment is a hallmark of humanity. Just about every decade, the United Nations publishes data on marriage and divorce in societies around the world. When I surveyed the available data for 97 societies in the 1980s, I found that 93 percent of women and 92 percent of men had married by age 49; currently 91 percent of Americans marry by age 49. Almost all men and women in traditional societies wed. While some 83 percent of these cultures permit a man to take more than one wife at once, in about two-thirds of them, fewer than 20 percent of men actually take two or more wives simultaneously; in the balance of these societies only around 20 percent of men engage in polygyny at some point during their lives. Just one half of one percent of cultures permit a woman to take more than one husband simultaneously. In sum, the vast majority of human beings everywhere marry one person at a time, the practice scientists call monogamy or pair bonding.

The brain circuitry for this male/ female attachment could have evolved at any time in human evolution; but, because monogamous attachment is not characteristic of the African apes, and because it is universal in human societies, I would venture that this brain system may have evolved soon after our ancestors descended from the fast-disappearing trees of East Africa some four million years ago. With the emergence of an upright human stride, females became obliged to carry their infants in their arms instead of on their backs. How could a female carry the equivalent of a 20-pound bowling ball in one arm and tools and weapons in the other, and still protect and provide for herself effectively? Females began to need a mate to help them while they nursed and carried young. A male would have had considerable difficulty attracting, protecting, and providing for a harem as he wandered the East African plains. But he could defend and provide for a single female and her infant. So, over time, natural selection favored those with the genetic propensity to form pair bonds—and the human brain chemistry for attachment evolved.

This male/female attachment is the foundation of human social life, but it also can lead to trouble. People with strong feelings of attachment can become “clingy.” Others may abuse or even kill a mate whom they believe to be inattentive or unfaithful.

Divorce and Serial Monogamy

Human monogamy is not always permanent, of course. Almost everywhere in the world, divorce is permitted and practiced. I maintain that even this human tendency stems in part from the brain circuits associated with the emotion system for attachment, although many cultural factors contribute to the relative frequency of divorce in a given society. Divorce rates, for example, are correlated with economic autonomy; in societies where spouses are relatively economically independent of one another, divorce rates are high. But several patterns for divorce, derived from the statistics on 62 industrial and agricultural societies in the Demographic Yearbooks of the United Nations, occur both where divorce rates are high and where divorce is rare. My hypothesis is that these more nearly universal patterns of marital decay evolved, and that someday the underlying neural mechanisms for these specific patterns of detachment will be found.

Among these patterns, the United Nations data indicate that people tend to divorce during and around the fourth year of marriage, and often while in their twenties, the height of reproductive and parenting years. Men and women also most frequently abandon a partnership that has produced no children or one dependent child; and most divorced individuals of reproductive age remarry. Moreover, the longer the union lasts, the older the spouses get, and the more children they bear, the more likely a couple is to remain together. There are many exceptions to these patterns, but, overall, people around the world tend to form a series of attachments.

A look at attachment behavior in other species suggests that these patterns are innate. Serial pair bonding is common in birds. Individuals in more than 90 percent of the approximately 9,000 species of birds form a pair bond at the beginning of the mating period. But in more than half of these avian species, partners do not pair for life; they go their separate ways at the end of the breeding season. Only 3 percent of mammals form pair bonds to rear their young, but the same habit of seasonal pairing prevails. For example, red foxes pair only for the breeding season. A male and female become a pair in mid-winter and rear their young together through the early summer months. But when the kits begin to wander, the dog fox and the vixen split to forage independently. Humans tend to divorce during and around the fourth year after marrying. This conforms to the traditional period between human successive births, which is also four years. So I have proposed that the worldwide human tendency to pair and remain together for about four years reflects an ancestral hominid reproductive strategy to pair and remain together through the breast-feeding and infancy of a single child. Once the youngster was able to join a multi-age play group at about age four, and be raised by older siblings, aunts, grandmothers, and other members of the hunting/gathering band, both partners could choose new mates and bear more varied young. Thus modern serial marriage patterns are probably a remnant of an ancestral breeding season.

“Every bed has been condemned, not by morality or law, but by time,” wrote poet Anne Sexton. This restlessness in long relationships probably has a physiological correlate in the brain. That correlate is not yet known, but I suspect that, over time, either the receptor sites for attachment chemicals become over-stimulated, or the brain produces less of these compounds, leaving the individual susceptible to estrangement and divorce.

Assimilating the Forces of Biology and Culture

Countless human habits, traditions, and artifacts stem from the evolution of these three emotion systems: lust, attraction, and attachment. Among them: the nuclear family; our myriad customs for courtship; our procedures for marriage; our terms for kin; and the plots of many great operas, novels, plays, films, songs, and poems. But these brain systems also contribute to the worldwide incidence of rape, stalking, homicide, suicide, and clinical depression, as well as the frequency of adultery and divorce.

Are we puppets on a string of DNA? Can we control our sexual and family lives? Should scientists seek ways to medicate stalkers and spouse abusers? Should lawyers, judges, and legislators view the serial rapist as a chemically disabled person? What we know about the brain systems for lust, attraction, and attachment as yet suggests only directions, not definite answers.

For example, I believe that brain chemistry plays a role in many serious, violent crimes. As scientists learn more about the brain, more lawyers and judges will be obliged to take this biological component into consideration in deciding the punishment of serial rapists, stalkers who murder, and perennial spouse abusers.

I think biology plays a less consequential role in the plight of all the normal men and women who struggle with inappropriate sexual yearnings, the “roving eye,” restlessness in long relationships, and other artifacts of evolution that threaten to destroy their family lives. Here is my supposition. Along with the evolution of the brain circuits for the sex drive, romantic love, marriage, and divorce, other brain networks emerged as well. The most important was a neural system that enables us to rise above our inappropriate or inconvenient mating tendencies.

Central to this system is the prefrontal cortex, a region of the brain that lies directly behind the forehead; this expanded dramatically during human prehistory. Neuroscientists have dubbed this region of the brain the “central executive” or the “crossroads” of the mind because it has connections to many sections of the brain and body and is devoted to the active processing of information. With the prefrontal cortex (and its connections) we keep track of the myriad bits of data that register in our brains, order and weigh them as they accumulate, and find patterns in them. Using the prefrontal cortex and its connections, we also reason hypothetically, analyze contingencies, consider options, plan for the future, and make decisions.

The mind assembles data in novel patterns, so with the emergence of the prefrontal cortex, humans acquired a brain mechanism that enabled them to behave in unique ways—ways qualitatively different from behavior emanating from biology or experience alone. Indeed, given the impressive decision-making power of the prefrontal cortex, this agglomeration of brain tissue is probably the locus of what we term, variously, the self, ego, or psyche.

In other words, I believe that biology and culture—nature and nurture—are but two of the major forces shaping human behavior. The third is our psyche, our capacity for reason, choice, and self-directed action. The three forces always interact, of course. Biology predisposes us to love in general ways. Cultural experiences modify those predispositions, overriding some, accentuating others. Yet each of us assimilates the forces of biology and culture in his own fashion. We are capable of monitoring and at times overriding the power of lust, attraction, attachment, and detachment. We have evidence of that power. Some 75 percent of American men and 85 percent of American women report that they are not adulterous. Half of all Americans marry for life.

In the movie The African Queen, Katherine Hepburn remarks to Humphrey Bogart, “Nature, Mr. Alnutt, is something we were put on this earth to rise above.” As scientists discover more about the interactions among brain systems and brain regions, I predict that they will come to appreciate the pivotal role of the psyche in directing human action. Because of this brain architecture, I think that those in the medical and legal communities will come to be convinced that most men and women have the physiological capacity to refrain from stalking a rejecting partner. Most people can overcome their restlessness in long relationships; and most can say no to adultery and divorce.

Certainly physicians should continue to use their knowledge of brain chemistry to alleviate the clinical depression that can be associated with romantic rejection. Even stalkers probably should be treated chemically. But from the perspective of the legal and medical communites, most of us are, in large part, responsible for how we love.

So scientists are beginning to answer Shakespeare’s question, “what t’is to love.” This panoply of feelings stems from three primary and primordial circuits in the brain for lust, attraction, and attachment. But this academic knowledge can never destroy the actual satisfaction, craving, or ecstasy of loving. From deep in the emotional furnace of the mind comes chemistry that carries the magic of love.