Why We Love (7 page)

Then most animals become exceedingly possessive of their prize.

Possessiveness

“Yourself—your soul—in pity give me all / Withhold no atom’s atom or I die.” Keats wanted to possess every bit of his beloved. Many other creatures share his sentiment. Some birds and mammals will fight almost until death to possess a lover exclusively.

During the June mating season, for example, the male grizzly bear attends a female for several days or even weeks, although he will depart after a while if he sees other mating opportunities. Observing a veteran male grizzly in Yellowstone National Park, naturalist Thomas McNamee writes, “In the nest of leaves and branches that was their day bed, he would lie with a protective and possessive paw across her shoulder. When other male grizzlies came near … the merest grunt would usually suffice to send any would-be contender off.”
35

An unhappy example of this possessiveness was observed in mountain bluebirds by zoologist David Barash.
36
The mating season had begun and a male and female mountain bluebird had built their nest and settled in. While the male was off foraging, however, Barash placed a stuffed male mountain bluebird on a tree limb beside the nest. Bedlam ensued. When the “husband” returned and saw the intruder, he viciously and repeatedly attacked the dummy. Then he turned on his mate, brutally attacking her, tearing out two of her primary flight feathers. She fled. The male soon appeared with a new female with whom he reared a brood.

While possessiveness drives some creatures to violence, jealousy plunges others into depression. Remember Violet, the little pug dog who was in love with Bingo, another pug? Violet doted on her “husband.” They were partners. “Like two little married people, they had their private arrangements,” writes Elizabeth Marshall Thomas, even “the way they liked to sleep.” Violet’s troubles started the day the young and beautiful husky, Maria, came to live in the Marshall household. Thomas writes of Violet’s jealousy, “What bothered Violet most about Maria, though, was that Bingo liked her so much. Ignoring Violet, Bingo spent time every day trying to make a conquest of Maria by parading back and forth beside her with his ears low, his expression soft and his tail very faintly wagging. Violet often tried to stop him.” No luck. Eventually Violet “would withdraw to a distant corner and sit down, chastened and depressed.”
37

Our closest relatives, “common” chimpanzees and bonobos, can also be highly possessive—even though they are promiscuous by nature. At the height of estrus, a female often visits one male, then another, sometimes copulating with over a dozen suitors in a day. Most calmly wait their turn. But some male chimps become possessive. And as their passion grows, they try to establish an exclusive partnership with a particular female.

Such was Satan, a chimp living in the Gombe Stream Reserve, Tanzania. Jane Goodall writes of Satan’s budding liaison with Miff. Miff had just come into “heat” and all the males knew it. The morning had started noisily as she passed from one male to the next, presenting her buttocks and coupling with each. But the day drew on and one by one, the males shuffled off through the bushes to eat or rest. Satan waited until the last of the other admirers had departed. Then as Miff roused herself to follow them, Satan jumped in front of her in the trail and walked casually in a direction not taken by the other males. He continually looked over his shoulder to see if she was following him. She was.

After half an hour Miff heard the other males calling through the foliage. For a moment she looked toward the voices, then directly at Satan, who was shaking branches impatiently to distract her. She paused, as if weighing her alternatives. Then she followed Satan over a ridge to a nearby valley—far from all the other males.
38

Often an estrous female chimp stays in the community to copulate with almost all the males. If she is attracted to an admirer, however, she may accompany this “special” individual to the periphery of their home range, remaining with him from three days to almost three months. Goodall calls these temporary partnerships “going on safari.”

Mate Guarding

Because possessiveness is so common in nature, animal behaviorists have given it a name: mate guarding.
39
They regard this taste for sexual exclusivity as a primary aspect of courtship in many species. Generally it is the male who guards the female—from poachers, and from defection by the female. For sound evolutionary reasons. If a male can sequester a female during her ovulation, she may bear his offspring and pass his genes toward eternity.

Males of species that form pair-bonds to rear their young have a second Darwinian motivation to be sexually possessive. It is not adaptive for a male to expend his vital time and energy building a nest, protecting a female, battling intruders, even feeding young—unless these babies carry his DNA. If his female cavorts with another male, he risks being cuckolded. So in socially monogamous species, males tend to be highly sensitive to intruders as they court and “wed.” Some male monkeys bite a female’s neck if she wanders off or herd her with taps or shoves; males of many other species fiercely defend a territory where a mate resides instead.

The men and women who participated in my survey (discussed in chapter one) also showed this tendency toward mate guarding, particularly the men. Men were much more likely than women to disagree with the statement: “It is good to be out of touch with _____ for a few days so that the anticipation can build up again” (Appendix, #4). This could be because women generally have more friends, more connections, more family ties, and more responsibilities outside of their love relationship. But men are probably also unconsciously driven to guard the vessel that may bear their seed.

They have good reason. In a recent poll of American men and women, 60 percent of men and 53 percent of women admitted to “mate poaching”; they had tried to woo another’s lover away to make a new committed partnership with them.
40
In fact, a study of thirty cultures showed how common mate poaching is around the world.
41
So like mountain bluebirds, humans are possessive.

The human tendency to stalk, even murder a straying lover probably comes from this animal tendency to guard a mate.

An Immodest Proposal

All these data have led me to believe that animals big and little are biologically driven to prefer, pursue, and possess specific mating partners: there is chemistry to animal attraction. And this chemistry must be the precursor of human romantic love.

But what brain chemicals are involved?

Two closely related natural stimulants in the mammalian brain appear to play a role: dopamine and norepinephrine. All birds and mammals are endowed with similar forms of dopamine and norepinephrine, as well as similar structures in the brain to produce and respond to these natural “uppers”—although these brain structures and circuits vary from one species to the next.

More important, dopamine and norepinephrine play a crucial role in sexual arousal and heightened motivation in birds and mam-mals.
42
For example, female laboratory rats express their amorous intentions by hopping and darting, behaviors associated with increased levels of dopamine.
43
And in prairie voles, little creatures much like field mice, elevated levels of dopamine in the brain are directly associated with a
preference
for a particular mating partner.
44

Please meet the prairie vole. These tiny animals live in a maze of tunnels and burrows on the grasslands of the American Midwest. Voles form pair-bonds to rear their young. The male leaves home soon after puberty to find a “spouse.” When he sees a likely candidate, he begins to court her avidly. Sniffing, licking, nuzzling, mounting: a vole couple copulates over fifty times in roughly two days. After this sex marathon, the male starts to behave like a new husband, building a nest for their forthcoming infants, ferociously guarding his mate from rival males, and defending their mutual home range. Some 90 percent of prairie voles live in lifelong unison with a single partner.
45

But prairie voles are choosy, as this study showed. Scientists paired an estrous female prairie vole with a male. As the female copulated with this suitor, she formed a distinct partiality for him, a favoritism that was accompanied with a 50 percent increase of dopamine in the nucleus accumbens, a part of the mammalian brain associated with craving and addiction in people.
46

Equally telling, when scientists injected a specific region of the female prairie vole’s brain with a substance that reduced levels of dopamine, she no longer preferred this partner over other males. And when the female was injected instead with compounds that increased brain levels of dopamine, she began to prefer the male who was present at the time of infusion—even though she had never mated with this individual.
47

Dopamine appears to play a key role in animal attraction.

Norepinephrine may contribute to this magnetism. When scientists put a drop of male urine on the upper lip of a female prairie vole, levels of norepinephrine elevate in the brain. This contributes to the release of estrogen and stimulates courting behavior.
48
Is the female prairie vole “attracted” to this scent?

Levels of norepinephrine (and dopamine) also spike as an estrous female sheep looks at slides of male sheep’s faces.
49
Maybe these ewes are temporarily infatuated with these rams.

Norepinephrine is even linked with a specific mammalian courting pose: lordosis—the female habit of crouching, arching her back, and tipping up her buttocks toward her suitor to advertise sexual availability.
50
Women do this, too. A woman will look coyly over her shoulder at a man as she gracefully arches her back and tips her buttocks in his direction.

These data led me to suspect that dopamine and/or norepinephrine play a role in animal attraction.

More brain chemicals are undoubtedly involved. As elephants, foxes, squirrels, and many other animals sift through their mating opportunities, they must distinguish colors, shapes, and sizes, listen for seductive tones, remember past successes and disasters, and sniff, touch, and taste to gather information about their potential consorts. A lot of chemical systems undoubtedly coordinate in some sort of chain reaction to trigger feelings of animal attraction.

But animals love. Tia, Bad Bull, Skipper, Misha, Maria, Violet, Thalia, Alexander, Miff, Satan, and just about every other mammal and bird on this planet has probably felt drawn to
specific
others. Temporarily charmed, these lovers step to a universal beat, croaking, barking, flapping, trilling, strutting, staring, nuzzling, patting, copulating—and adoring—their preferred mating partners.

When the brain chemistry for animal attraction first evolved no one knows. I suspect that by the time the first primitive mammals were scampering beneath the feet of dinosaurs, these primordial whiskered brethren of humankind had evolved a simple brain network to motivate them to distinguish among suitors and prefer particular ones. With this rudimentary equipment, they went forth to multiply, spreading this chemistry to myriad swimming, flying, creeping, hopping, leaping, trotting, swinging beings, including the ancestors of apes and humans.

Men and women of ancient India called romantic love “the eternal dance of the universe.”
51
They were right. How long a chipmunk, a zebra, or a whale actually feels attracted to a special mate obviously varies, however. Environments vary. Needs vary. And species vary. In rats, attraction probably lasts only seconds. Elephants appear to be “in love” about three days. Dogs often show attraction for months and attachment for many years. Some scientists question how “conscious” these creatures are of their emotions.
52
No one knows. But animals express heightened energy, focussed attention, euphoria, craving, persistence, possessiveness, and affection: animal attraction. And data suggest that this attraction is associated with two common brain chemicals—dopamine and norepinephrine.

Could these chemicals also play a role in human romantic love? To understand the chemistry of this “eternal dance,” I decided to look inside the human brain.

3

Chemistry of Love:
Scanning the Brain “in Love”

For love is as strong as death.

Its passions are as cruel as the grave

And its flashes of fire are the very flame of God.

The Song of Songs (c. 900–300
B.C.E
.)

“There is the heat of Love, the pulsing rush of Longing, the lover’s whisper, irresistible—magic to make the sanest man go mad.”
1
This magic that Homer sang of in
The Iliad
has started wars, sired dynasties, toppled kingdoms, and generated some of the world’s finest literature and art. People sing for love, work for love, kill for love, live for love, and die for love. What causes this sorcery?

As you know, I have come to believe that romantic love is a universal human feeling, produced by specific chemicals and networks in the brain. But exactly which ones? Determined to shed some light on this magic that can make the sanest man go mad, I launched a multipart project in 1996 to collect scientific data on the chemistry and brain circuitry of romantic love. I assumed that many chemicals must be involved in one way or another. But I focussed my investigation on dopamine and norepinephrine, as well as a related brain substance, serotonin.

I looked into the nature of these chemicals for two reasons: the attraction animals feel for particular mates is linked with elevated levels of dopamine and/or norepinephrine in the brain. More important, all three of these chemicals produce many of the sensations of human romantic passion.

Rock On, Sweet Dopamine