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Review / Books: Molecules of Desire

By Christopher F. Chabris
1,133 words
13 February 2004
The Wall Street Journal
(Copyright (c) 2004, Dow Jones & Company, Inc.)


By Helen Fisher

(Henry Holt & Company, 301 pages, $25)

EVERY YEAR about this time, the most baffling of human emotions -- and perhaps the most profound -- gets reduced to a few commercial offerings of enchanting simplicity: a greeting card, a box of candy, a bouquet of roses, an expensive dinner. Nothing could be easier.

But woe to those who do not give Valentine's Day its due, for it turns out that a great deal is at stake in its rituals. In "Why We Love," Rutgers anthropologist Helen Fisher looks deep inside human biology to explain the force of romantic passion and its abiding hold on our conduct and desire.

She begins by reviewing the many ways in which being in love, or pursuing a romance, changes the way we act. Most obviously it causes us to spend large sums of money and time on someone we aren't even related to. But that's just a beginning. Love alters sleep patterns, synchronizes partners' moods, accelerates heartbeats, engraves memories and stirs up powerful and sometimes uncontrollable emotions beyond the feeling of love itself.

There is, though, nothing capricious about love, despite the sonneteers' laments. Romantic behavior is observable across cultures and species. It involves, famously, displaying signs of one's genetic value, engaging in courtship rituals, and protecting and bonding with a mate. Indeed, the universality of such conduct suggests that human love is the product of brain mechanisms that have been present throughout the "recent" millennia of evolution.

To find these mechanisms, Ms. Fisher and some scholarly colleagues -- including medical researchers -- scanned the brain activity of people who claimed to have "just fallen madly in love," as the study's recruiting poster put it. After documenting their passion in a questionnaire and two-hour interview, the study-subjects entered an MRI scanner and viewed pictures of their lovers.

The results? Compared with seeing pictures of mere acquaintances, the act of looking at lovers had the effect of activating parts of the brain's "reward system," which responds also to such treats as cocaine and food. Since the neurons in this brain circuit communicate using the chemical messenger dopamine, Ms. Fisher infers that dopamine is the molecule primarily responsible for romantic feeling and action.

Indeed, Ms. Fisher calls dopamine "the liquor that fuels romance." Jack Daniels might beg to differ, but Ms. Fisher offers more evidence than her own experiment. She notes that dopamine-increasing antidepressant drugs may increase sex drive as well. This effect, she argues, stands in contrast to serotonin-modulating drugs, such as Prozac, which may reduce libido, cause other people's faces to seem less attractive and, perhaps as important, make orgasm more difficult to achieve.

But wait a minute. Are attraction and sex the touchstones of romantic love? They happen all the time without it. There is, in short, a problem for Ms. Fisher's broad conclusion: Dopamine and its rewards are not specific to romance. Other studies show that the brain's reward system responds not only to pictures of lovers -- as Ms. Fisher found -- but also to pornographic images and to beautiful faces in general (of either sex).

Of course, Ms. Fisher is well aware that there is more to human mating than romantic love. She theorizes that the capacity for love evolved as part of a three-part mechanism to promote successful reproduction. The other two parts are lust, which usually comes first, and attachment, which usually comes last. As most of us know from cruel experience, relationships often begin with elemental attraction -- to physical appearance, personality traits and social status -- and then may progress to romantic love and feelings of contentment and security, but the path is rarely smooth. Part of the problem is that men and women differ on the emphasis that they give each of these stages.

Ms. Fisher turns to research in evolutionary psychology to explain such differences and to note a few similarities too. For example, despite male proclivities, humans are among the most monogamous of primate species. Ms. Fisher suggests that humans became monogamous -- at least serially -- because they were bipedal, walking exclusively upright. Chimpanzee mothers could carry their young on their backs, leaving their arms free to grab food and care for children as "single parents." Early human ancestors had to use their arms to carry children, making it difficult to collect food at the same time. With a male regularly in the picture, however, duties could be shared.

A provocative story, but is it true? And if so, how exactly did such mental adaptation to monogamy happen? What genes were added, subtracted or modified to enable the male brain to focus on pursuing one woman and staying with her to raise their children? Ms. Fisher does not tell us, but this is because nobody knows. The science has not yet caught up with the speculation.

The downside of the high hopes of romantic love, of course, are the feelings of depression and abandonment that come when a relationship ends. Ms. Fisher documents these emotions not only with science but also with snippets of poetry, both familiar and obscure. Even more provocative than her thesis on bipedalism and monogamy is her account of why, on average, marriages that end in divorce last about four years.

She observes that the females among our distant ancestors, about 3.5 million years ago, typically stayed with a partner just long enough to bear a child, nurse it and raise it to the point where the mother's extended family could care for it, leaving both parents free to seek new partners. Perhaps this four-year span reflects the work of a brain circuit that evolved to promote attachment. Like any adaptive mechanism, though, it was just strong enough to promote reproduction. After four years, at least for some couples, the cycle may be complete.

There is solid scientific evidence to back the claim that different brain systems underlie lust, romance and attachment, with reproduction as their unifying goal. But to say that such systems are different is not to say that they operate separately. As with dopamine and romantic love, Ms. Fisher plays down the overlap among systems. Many parts of the brain and many different chemical messengers are involved in every human action, and the evidence is still tenuous for just how they fit together.

Understanding this kind of complicated "relationship" is the central project for the growing field of social neuroscience in the coming years. Meanwhile, Ms. Fisher's book is a provocative introduction to the topic, even though jewelry may still make a better Valentine's Day gift.


Mr. Chabris is a research associate in the Department of Psychology at Harvard University.

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