Why We Love (12 page)

This relationship between elevated levels of dopamine and sexual arousal, frequency of intercourse, and positive sexual function is common in animals.
29
When dopamine is injected into a male rat’s bloodstream, for example, it stimulates copulatory behaviors.
30
Moreover, when a male laboratory rat is placed in an adjacent cage where he can see or smell an estrous female, he becomes sexually excited; with this, levels of dopamine also rise.
31
And when the barrier is removed and he is allowed to copulate, levels of dopamine rise even higher.
32

Dopamine can also stimulate lust in humans.
33
When men and women who are depressed take drugs that elevate levels of dopamine in the brain, their sex drive regularly improves.
34

A friend of mine in her thirties told me a remarkable story regarding this. She had been mildly depressed for several years, so recently she began to take one of the newer antidepressants (one without negative sexual side effects) that elevates levels of dopamine in the brain. A month after starting this drug she not only thought more about sex, but she had also begun to have multiple orgasms with her boyfriend. I suspect her sudden change in sexual desire and sexual function occurred because the pill she was taking daily to enhance dopamine triggered the release of testosterone as well.

This positive relationship between dopamine and testosterone may also explain why people feel so sexy when they go on vacation, try some new trick in the bedroom, or make love to a new partner. Novel experiences drive up levels of dopamine in the brain—hence they can also trigger the brain chemistry of lust.

Norepinephrine, another stimulant that probably plays a role in romantic love, also stimulates the sex drive. Addicts who take amphetamines, known as “uppers” or “speed,” say their sex drive can be constant. This lustiness probably stems from the same biological equation: amphetamines largely boost norepinephrine (as well as dopamine). And norepinephrine can stimulate the production of testosterone.
35

Once again some caveats: the dosage of all these chemicals, as well as the timing of their release in the brain, makes a difference. None of these interactions are direct or simple. But generally speaking, dopamine and norepinephrine spark sexual desire,
36
most likely by elevating levels of testosterone. No wonder new lovers stay up all night caressing. The chemistry of romance ignites the most powerful urge of nature: the drive to copulate.

This chemical connection between romantic love and lust makes evolutionary sense. After all, if romantic love evolved to stimulate mating with a “special” other, it
should
trigger the drive to have sex with this beloved, too.

Does Lust Trigger Romance?

But is the reverse true? Can lust stimulate amour? Can you climb in bed with “just a friend” or even a stranger, then suddenly fall in love with him or her?

Ovid, a man who had many love affairs, believed that a strong sexual attraction could often provoke a person to fall in love.
37
But lust does not always trigger romantic ardor, as many people know. Most sexually liberated contemporary adults have had sex with someone they were not in love with. Many have even copulated with this “friend” regularly. But, alas, they never felt the exhilaration of romantic passion for this bed partner. Lust does not necessarily lead to the passion and obsession of romantic love.

In fact, there is a great deal of data to the contrary. Athletes who inject synthetic androgens to build muscles don’t fall in love as they take their drugs. When middle-aged men and women inject testosterone or apply testosterone cream to various body parts to stimulate their sex drive, their sexual thoughts and fantasies increase.
38
But they don’t fall in love either. The brain circuitry of lust does not necessarily ignite the furnace of romance.

This is not to say that lust never triggers romantic love. It can. A middle-aged friend of mine is a good example. She had been having sex with “just a friend” for almost three years. These were sporadic events, she told me; she and her friend had sex no more than two or three times annually. Then one summer evening, about five minutes after coupling with him, she fell profoundly in love with him. At that moment the obsessive thinking, the pining, and the rapture started. In the weeks and months that followed, she told me, she lay awake at night and thought of him constantly, waited by the phone to hear his voice, dressed attractively to win him, and fantasized about a life together. Fortunately he loved her, too.

“
Naso pasyo, maya basyo.
” Women in rural western Nepal use this off-color saying to express the same phenomenon. It means, “The penis entered and love arrived.”
39

I think biology contributes to this spontaneous love for a sex partner. Sexual activity can increase brain levels of dopamine and norepinephrine in male rats.
40
Even without sexual activity, increasing levels of testosterone can elevate levels of dopamine
41
and norepinephrine
42
as well as suppress levels of serotonin.
43
In short, the hormone of sexual desire can trigger the release of the brain’s elixirs for romantic passion. As my friend cuddled and copulated with “just a friend,” I think she triggered her brain circuit for romance and fell in love.

That “ol’ black magic” is a fickle force. The chemistry of romantic love can trigger the chemistry of sexual desire and the fuel of sexual desire can trigger the fuel of romance. This is why it is dangerous to copulate with someone with whom you don’t wish to become involved. Although you intend to have casual sex, you might just fall in love.

Romantic passion also has a special relationship with feelings of attachment.

On Attachment

“Who ordered that their longing’s fire / Should be, as soon as kindled, cooled?”
44
Poet Matthew Arnold mourned the passing of romantic love.

Love changes over time. It becomes deeper, calmer. No longer do couples talk all day or dance till dawn. The mad passion, the ecstasy, the longing, the obsessive thinking, the heightened energy: all dissolve. But if you are fortunate, this magic transforms itself into new feelings of security, comfort, calm, and union with your partner. Psychologist Elaine Hatfield calls this feeling “companionate love,” a feeling of happy togetherness with someone whose life has become deeply entwined with yours.
45
I call this complex feeling “attachment.”

And just as men and women intuitively distinguish between the feelings of romantic love and those of lust, people just as easily distinguish between feelings of romance and attachment.

Nisa, a !Kung Bushman woman of the Kalahari Desert of Botswana, explained this feeling of man-woman attachment succinctly to anthropologist Marjorie Shostak. “When two people are first together,” Nisa said, “their hearts are on fire and their passion is very great. After a while, the fire cools and that’s how it stays. They continue to love each other, but it’s in a different way—warm and dependable.”
46

The Taita of Kenya would agree. They say that love comes in two forms, an irresistible longing, a “kind of sickness,” and a deep enduring affection for another.
47
Brazilians have a poetic proverb that distinguishes between these two feelings, saying, “Love is born in a glance and matures in a smile.”
48
And for the Koreans, “
sarang
” is a word close to the Western concept of romantic love, while “
chong
” is more like feelings of long-term attachment. But perhaps Abigail Adams, the wife of America’s second president, said it best, writing to John in 1793, “Years subdue the ardor of passion, but in lieu thereof friendship and affection deep-rooted subsists, which defies the ravages of time, and whilst the vital flame exists.”
49

The Chemistry of Attachment

Scientists began to examine this brain system, attachment, decades ago when British psychiatrist John Bowlby proposed that humans have evolved an innate attachment system consisting of specific behaviors and physiological responses.
50
Only recently, however, have researchers begun to understand which brain chemicals produce this feeling of fusion with a long-term mate. Most now believe that vasopressin and oxytocin, closely related hormones made largely in the hypothalamus and the gonads, produce many of the behaviors associated with attachment.

But to grasp how these hormones generate the sensation of union with a sweetheart, I must reintroduce you to the American midwesterners discussed earlier: prairie voles. As you recall, these brown-gray, mouselike rodents form pair-bonds to rear their young; some 90 percent mate for life with a single partner. A few years ago neuroscientists Sue Carter, Tom Insel, and others pinpointed the cause of this attachment in males. As the male prairie vole ejaculates, levels of vasopressin increase in the brain, triggering his spousal and parenting zeal.
51

Is vasopressin nature’s cocktail for male attachment?

To investigate this hypothesis, scientists then injected vasopressin into the brains of
virgin
male prairie voles raised in the lab. These males immediately began to defend the space around them from other males, an aspect of pair formation in prairie voles. And when each was introduced to a female, he became instantaneously possessive of her.
52
Moreover, when these same scientists blocked the production of vasopressin in the brain, male prairie voles acted like cads instead—copulating with a female, then abandoning her for another mating opportunity.

Nature has given male mammals a chemical to feel the paternal instinct: vasopressin.

Oxytocin: Another Cocktail for Devotion?

“So we grew together, / Like to a double cherry, / seeming parted, / But yet a union in partition; / Two lovely berries moulded on one stem.”
53
Few poets write about the durable feeling of attachment, perhaps because this drive rarely compels one to compose passionate verse in the dead of night. These lines by Shakespeare are an exception. Yet the feeling of attachment must be a common sensation among all birds and mammals, because it is associated not only with vasopressin but also with oxytocin—a related hormone that is ubiquitous in nature.
54

Like vasopressin, oxytocin is made in the hypothalamus, as well as in the ovaries and testes. Unlike vasopressin, oxytocin is released in all female mammals (including women) during the birthing process.
55
It initiates contractions of the uterus and stimulates the mammary glands to produce milk. But scientists have now established that oxytocin also stimulates bonding between a mother and her infant.

More important, many now believe that oxytocin is also involved in the feelings of adult male-female attachment.
56

You have undoubtedly felt the power of these two “satisfaction hormones,” as vasopressin and oxytocin are sometimes called. We secrete them at two poignant moments during sexual intercourse: during stimulation of the genitals and/or nipples
57
and during orgasm. At orgasm, levels of vasopressin dramatically increase in men and levels of oxytocin rise in women.
58
These “cuddle chemicals” undoubtedly contribute to that sense of fusion, closeness, and attachment you can feel after sweet sex with a beloved.

How does the chemistry of attachment affect feelings of lust and romantic love?

Does Lust Dampen Attachment?

The chemical components of attachment have complex effects on both the sex drive and feelings of romantic passion.

Under some circumstances, testosterone can elevate levels of vasopressin
59
and oxytocin
60
in animals, increasing attachment behaviors such as mutual grooming, scent marking, and defending a nesting site.
61
The reverse can also happen: oxytocin and vasopressin can increase testosterone production under some conditions.
62
In short, the chemistry of attachment can trigger lust and the chemistry of lust can trigger expressions of attachment.

But all these hormones can also have negative effects on one another. Increasing levels of testosterone can sometimes
drive down
levels of vasopressin (and oxytocin) and elevated levels of vasopressin can
decrease
levels of testosterone.
63
This inverse relationship between lust and attachment is “dose-dependent”; it varies depending on the quantities, timing, and interactions among several hormones.
64
But high levels of testosterone can reduce attachment. And there is a great deal of evidence that this happens to people regularly—sometimes with disastrous effects.

Men with high baseline levels of testosterone marry less frequently, have more adulterous affairs, commit more spousal abuse, and divorce more often. As a man’s marriage becomes less stable, his levels of testosterone rise. With divorce, his testosterone levels rise even more. And single men tend to have higher levels of testosterone than married men.
65

The reverse can also happen: as a man becomes more and more attached to his family, levels of testosterone can decline. In fact, at the birth of a child, expectant fathers experience a significant decline in levels of testosterone.
66
Even when a man holds a baby, levels of testosterone decrease.

This negative relationship between testosterone and attachment is also seen in other creatures. Male cardinals and blue jays flit from one female to the next; they never stick around to parent their young. These profligate fathers have high levels of testosterone. Males of species that form monogamous pair-bonds and remain with this mate to father infants, however, have much lower levels of testosterone during the parenting phase of the breeding season.
67
And when scientists surgically pumped testosterone into monogamous male sparrows, these faithful fathers abandoned their nests, their young, and their “wives” to court other females.
68