You Dirty Vole

Researchers weren't particularly surprised by the parts of the lovers' brains that were active. What astonished them was that two other brain areas were suppressed-the amygdala and the right prefrontal cortex. The amygdala is associated with negative emotions like fear and anger. The right prefrontal cortex appears to be overly active in people suffering from depression. The positive emotion of love, it seems, suppresses negative emotions. Might that be the scientific basis for why people who are madly in love fail to see the negative traits of their beloved? "Maybe," says Bartels cautiously. "But we haven't proven that yet."


The idea that romantic love activates parts of the brain associated with addiction got Donatella Marazziti at Pisa University in Tuscany wondering if it might be related to obsessive compulsive disorder (OCD). Anyone who has ever been in love knows how consuming the feeling can be. You can think of nothing but your lover every waking moment. Some people with OCD have low levels of the brain chemical serotonin. Might love-obsessed people also have low serotonin levels? Sure enough, when Marazziti and her colleagues tested the blood of 20 students who were madly in love and 20 people with OCD, she found that both groups had low levels of a protein that shuttles serotonin between brain cells.


And what happens when the euphoria of "mad love" wears off? Marazziti tested the blood of a few of the lovers 12 to 18 months later and found that their serotonin levels had returned to normal. That doesn't doom a couple, of course, but it suggests a biological explanation for the evolution of relationships. In many cases, romantic love turns into compassionate love, thanks to oxytocin and vasopressin swirling inside the lovers' brains. This attachment is what keeps many couples together. But because attachment and romantic love involve different biochemical processes, attachment to one person does not suppress lust for another. "The problem is, they are not always well linked," says anthropologist Helen Fisher, who has written several books on love, sex, and marriage.

TYING IT ALL TOGETHER: THE TRAVELING SALESMAN AND THE MARRIAGE VOW

In the wild, about half of male voles wander the fields, never settling down with one partner. These "traveling salesmen," as Lowell Getz calls them, are always "trying to get with other females." Most females prefer to mate with their partners. But if they get the chance, some will mate with other males too. And, according to Jerry Wolff, a biologist at the University of Memphis, female voles sometimes "divorce" their partners. In the lab, he restricts three males at a time in separate but connected chambers and gives a female free range. The female has already paired with one of the males and is pregnant with his pups. Wolff says about a third of the females pick up their nesting materials and move in with a different fellow. Another third actually solicit and successfully mate with one or both of the other males, and the last third remain faithful.