We spend most of our lives pining for it, analyzing it, regretting it, and falling in and out of it. But do we ever really understand love and our complex behaviors surrounding it? In their book, “The Chemistry Between Us: Love, Sex, and the Science of Attraction,” neuroscientist Larry Young, Ph.D., and journalist Brian Alexander tackle the topic, including what role the brain plays in things like physical attraction, lust, fidelity, and family bonds. Brain World had a chance to interview the authors.

Brain World: Do we have control over who we fall in and out of love with, or are our brain chemicals really in control?

Larry Young and Brian Alexander: To some degree, we do have control, yes, but not quite the amount of control we often like to imagine.

We can, for example, control with whom we associate, or the places we go to meet people. When we do, we use the reasoning parts of our brains. But we argue that brain mechanisms — reward, empathy, trust — and the chemicals associated with them, put much of human bonding beyond our rational control.

In fact, love depends on a loss of rational control. If we were perfectly reasoning, perfectly rational, we’d never do it.

BW: Can the study of brain chemicals reveal which marriages will succeed?

LY & BA: We are skeptical of claims some are making that an individual’s relationship happiness can be reliably predicted based on a genetic (and therefore chemical) profile. (At least not yet!)

Having said that, however, certain genetic variations have been shown to be predictive of relationship happiness on a population-wide basis of large samples. [In the book], we suggest that eventually people may well choose to screen potential lovers based on such information. We imagine future personals ads promoting one’s brain chemical receptor status along with height, weight, and Porsche-driving.

BW: A few women might feel relieved that they can blame a certain “bad boy” in their past on their brains. How so?

LY & BA: Ha! Yes, it’s true. It relates to the previous answer. When women are ovulating, they are more likely to be attracted to “bad boys.” As an illustration, we follow an experiment using university women whose behavior changes toward men the experimenter calls “cads” when compared to the identical men who also play the role of nice guys. When the women are at their peak of fertility, they unconsciously flirt with the bad boys, the men who exude cocky confidence. During ovulation, a woman can be lured by her brain into falling for the bad boy, because her brain wants the fittest father of her babies.

BW: Does the brain register love and lust the same way?

LY & BA: No, though they are very intertwined. Lust is the lure that leads us into love. But love lasts even after lust has disappeared. You can see this in brain images. Love and lust look different. For example, when a woman in love with a man sees a picture of her lover, her brain displays an activation pattern that’s just about identical to the pattern she displays when she looks at her baby.

BW: Why do we remain in relationships long after the so-called fire has gone out?

LY & BA: Because we are addicted. We argue that love (not sex) is an addiction, and just as a meth or cocaine or heroin abuser loses the joy of the drug and transitions into dependence, people in love lose the fire but still can’t bear to be apart from each other. Why does a couple who rarely have sex anymore miss each other when they’re apart? Because they’ve become addicted to each other.

BW: Were you able to come up with a definitive answer on whether humans are hardwired to be monogamous or promiscuous?

LY & BA: We swear we’re not trying to fudge with this answer! But we argue that some are and some aren’t. It looks like about one-quarter to one-third of human beings aren’t naturally wired for monogamy, though we are all essentially wired to love. That’s why, throughout history, so many of our social rules, or religious strictures, address the issue. Why would they have to if all humans are “supposed” to be naturally monogamous?

Yet we’ve spent thousands of years wrestling with monogamy. This is what we call the “infidelity paradox.” Of course, if one-third of people aren’t really built for monogamy, that means most of us are. It’s also important to distinguish between social monogamy and sexual monogamy. We can be in love with our spouses, not want to be apart from them, and yet want to have sex with another. We conflate the two all the time, often deliberately, but they are not necessarily the same. As you can tell, love isn’t a fairy tale; it’s a pretty messy business.

This article was originally published in the Fall 2012 issue of Brain World Magazine.

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