WHAT IS LOVE?
"What 'tis to love?" Shakespeare asked. The great bard was not the first to wonder. I suspect our ancestors pondered this question a million years ago as they lay and watched the stars.
There are many kinds of love. But I have come to believe that during our long evolutionary past, human beings evolved three basic brain networks for loving as they courted, mated, reproduced and reared their young: lust, romantic attraction and attachment. And as days turned into centuries and nature weeded out those who failed to reproduce, natural selection hardwired these three distinct systems into the human brain.
Each brain system is associated with a different set of primary neurochemicals and brain networks. Lust--the craving for sexual gratification--is associated primarily with testosterone in both men and women. Romantic attraction--the elation, heightened energy, obsessive thinking, focused attention and yearning of new, fresh love--is associated with elevated brain activities of dopamine and norepinephrine, natural stimulants, and low activity of a related brain chemical, serotonin. And male-female attachment--the calm and emotional union one often feels with a long term partner--is associated with oxytocin and vasopressin.
Moreover, each of these brain networks evolved to direct a different aspect of human reproduction. Lust drives us to copulate with almost any remotely appropriate partner. Romantic attraction (romantic love, obsessive love or being in love) evolved to motivate us to prefer and pursue specific mating partners, thereby conserving precious courtship time and energy. And feelings of attachment evolved to enable new parents to remain together at least long enough to rear a child though infancy.
When nature makes a good design, she uses it over and over. And it is possible that almost all types of human love--from love of God to maternal love to brotherly love to all the other subtle varieties of human love--are variations of these three basic brain systems, mixing in myriad ways with one another and with other brain networks.
The brain system I am studying is romantic love. I began by culling from the scientific literature those mental and physical traits that people regularly express when they are madly in love. Next, I established that people everywhere, from the ancient Sumerians and Chinese to contemporary Tanzanians, Eskimos and Arabs, express these traits. From these preliminary investigations I concluded that romantic love is a universal experience--deeply embedded in the human brain. Moreover, I developed my hypotheses about the brain chemistry of this passion. Last, with collaborators Dr. Lucy L. Brown, Dr. Arthur Aron and several others, I used functional Magnetic Resonance Imaging (fMRI) to scan the brains of more than 40 men and women who were wildly in love. Half were loved in return; the rest had recently been rejected by someone they adored.
The results were remarkable. When lovers gaze at a photo of a beloved, they experience increased activity in a tiny "factory" near the base of the brain that produces and distributes dopamine to many brain regions. Dopamine is associated with excessive energy, elation, focused attention and the motivation to win rewards--basic traits of romantic love. We also found activity in several other brain regions rich in dopamine receptors and basic to the brain's "reward system."
These results changed my thinking about romantic love: This passion is a fundamental human mating drive. Like the craving for food, romantic love is a powerful physiological need, an urge, a motivation, an instinct that evolved specifically to enable men and women to court and win a preferred mating partner. Indeed, the drive to love is stronger than the sex drive. Few people kill themselves when someone denies them sex; many have committed suicide after being rejected by a beloved.
Our scanning team also found gender differences. Male subjects showed more activity in a brain region associated with the integration of visual stimuli. This makes evolutionary sense. For millions of years ancestral males needed to visually appraise a female's ability to bear healthy young. Women showed more activity in brain regions associated with memory recall. This, too, has evolutionary logic. Ancestral females needed to choose mates who could provide and protect. So females needed to remember what a lover promised yesterday and what he did (and didn't do) last week. Women still remember more details of a love affair than men.
These data also led me to hypothesize that animals feel primitive forms of romantic love. All mammals (and birds) have mating preferences. And as they court, they focus their attention on specific individuals, follow them obsessively, express intense energy and pat, lick, stroke and caress in tender ways. All are characteristics of romantic love. And this "animal attraction" has been associated with dopamine in the brain--just like human romantic love. Attraction lasts only seconds in rats, about three days among elephants, and months in dogs; but animals do love. In fact, they often express this attraction instantaneously--the forerunner of "love-at-first-sight."
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