Neither is driven by logic. Both drive behavior non-stop, on autopilot, below conscious awareness…

That’s the first sentence of a recently published article on the neurobiology of love in Scientific American Mind, which featured me as a writer and talking head. The author Yudhijit Bhattacharjee is a friend of mine who has done some great work for this magazine. Here are some more excerpts from the article:

Beneath all that selfless affection lies something far less noble—an inconvenient truth about brain anatomy that scientists have pieced together only in the past decade or so. It turns out that love is rooted in primitive parts of the brain, those associated with reward and addiction. Just as Phil grew addicted to the rush of infatuation, so might another person become hooked on the elation that accompanies feelings of love or even just on the warm fuzzies of deep friendship.

As scientists begin to map out the basic circuitry of social attachments, they also are homing in on what distinguishes a strong connection from one that fails spectacularly—along with many people’s cherished notions about why relationships end. Love apparently can be as blinding as it is empowering; it is not written into our brains by some higher power after all but rather cobbled together through an intricate dance of chemistry, circumstance, and attachment style.

“I’ve seen so many people who are clearly meant for each other be miserable together,” says Helen Fisher, a biological anthropologist at Rutgers University. “There seems to be no foolproof way to pick the perfect match.”…

Fisher says romantic love is not much different from our fondness for chocolate cake—both tap into essential drives that helped us adapt as humans. The dopamine-driven rush of infatuation evolved because it helped cement couples together at critical junctures in prehistoric times—when they needed to work as a team or when an infant was present (and thus required two parents). That same sensation also drives men and women to focus their mating energy on just one person at a time. Yet infatuation’s influence on the male brain is even more powerful, Fisher says. In a study of men and women who’d recently fallen madly in love, she found that those shown photos of their sweethearts activated far more neurons than those looking at pictures of friends or even neutral acquaintances. “The attraction system takes over,” she says…

Love, it seems, is not a single entity but rather a complex constellation of feelings and responses whose purpose varies depending on gender and age—and which might be different from one person to the next. Perhaps, as some researchers have suggested, romantic love evolved for men primarily as a drive to seek sex with many women; in contrast, women may have evolved to seek out partners whom they could count on for resources and help rear children.

For decades scientists have focused on what happens between two people in a relationship—from how their brain activity changes as they stare into each other’s eyes through the highs and lows of romance. But recently some researchers have begun exploring the individual motivations that make us seek out one particular person. “On our deathbed, most of us are unlikely to reflect back on whether we had sex with five or seven people,” says Helen Fisher, a biological anthropologist at Rutgers University who has studied the neural chemistry of love…

In one recent study, published in February in the journal PLoS One, researchers examined the brain scans of 30 men and women who had recently fallen madly in love. The scientists found that looking at a photo of their beloved activated one set of regions (in the nucleus accumbens) while looking at photos of friends activated other parts (in the ventral pallidum). “When you experience early-stage romantic love, it’s like cocaine or amphetamine,” says lead author Andreas Bartels, a neuroscientist at University College London.

The promiscuous dopamine system may be even more pronounced in men because testosterone diminishes their levels of oxytocin, which inhibits their urges. “Men are uniquely vulnerable to addiction because they’re more sensitive to the dopamine rush,” says Fisher, who conducted brain scans on men and women in three states of love.

“Of all the kinds of love we’ve looked at—romantic, maternal, even our fondness for ice cream—the romantic love system has been one of the most active,” says Arthur Aron, a psychologist at Stony Brook University in New York State who is studying how couples form close relationships over time. “It’s not enough to say that it causes you to lose sleep or skip meals; when people are in love they’re driven…

“Romantic love is not just a psychological state. It has important consequences for the body…It’s now well established that stress and anxiety, which activate fight-or-flight systems, can cause people to become more physically ill. And passionate love often involves arousal and intense motivation—the same brain systems activated during states such as fear and anger.”

“From an evolutionary perspective, it makes sense that we aren’t wired to fall into lust at first sight with every stranger we meet,” says Lucy Brown,…Indeed, bewitched men tended to swoon over their new wives in a way they hadn’t before marriage—and haven’t since. In fact, it took several centuries for scientists to realize this phenomenon even existed; until recently, many assumed that people married for practical, rather than romantic reasons.

Studies suggest that it takes about half a year for most couples to fall deeply in love…romantic attraction seems to peak at around 28; after 50, the brain is more likely to be registering other emotional nuances—like compassion or fondness—that fuel long-term relationships. “Our monkey studies show that females seek out males who are steady contributors,” says Fisher. The team recently found evidence of similar behavior in rats.”