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Why Love Sometimes Sucks

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Paul J. Zak is the author of the new book The Moral Molecule: The Source of Love and Prosperity (Dutton, $26.95)

A woman I dated briefly stalked me after we stopped seeing each other. She'd show up at my door at odd times and I'd run into her too often in the street. I became convinced she wanted to hurt me, so when I moved I left no trace of where I went.

Psychopathology? Or just brain chemicals out of balance?

In 2001, I started studying a then little-appreciated molecule called oxytocin that initiates uterine contractions during mammalian birth and milk flow during breastfeeding. What else might this ancient nurturing chemical do, I wondered?

A lot, it turns out. I found that oxytocin is the master "connection" molecule in human beings. It makes us care about our romantic partners, our kids, and our pets. But here's the weird part: when the brain releases oxytocin we connect to complete strangers and care about them in tangible ways. Like giving them money.

It was so easy, my experiments showed, to get the brain to make oxytocin. Touching, dancing, praying, and even a simple signal of trust by another caused the brain to synthesize oxytocin and make us care about others' welfare. I started calling oxytocin the "moral molecule" because the hallmark of moral behavior is care for another. What a curious molecule!

Care is the foundation of love. You cannot love someone that you don't care about. So why is love so damn hard?

Turns out evolution played a little trick on us. It gave us monogamous brains but promiscuous genitals. The oxytocin response means that when we mate (a potent oxytocin stimulus) we want to stay with that person at least for a while and perhaps forever. But, the human penis is designed to scoop another man's semen out of the female. This means males and females evolved to be promiscuous.

This is why love is complicated. Bonobos, one of our closest genetic relatives, have sex with both sexes, anytime, anywhere. They're the hippies of the animal kingdom. "If it feels good, do it" is their motto. We, on the other hand, worry incessantly and appropriately if he or she cares about us, or is just using us for sex. We can't help but do this because we have a big clump of oxytocin receptors in our brains that makes us feel good when someone loves for us, and when we love another. Just like we need food and water, we need to be loved.

That's true for 95% of the thousands of people I've studied. When they are shown care, these good folks release oxytocin and reciprocate in kind. But, the other 5% have a dysfunctional oxytocin system. They don't release oxytocin when others show them trust or care, they don't seem to feel empathy for others. Not surprisingly, they have a ton of sexual partners. They aren't able to connect with others for very long--if at all. Both men and women fall into this group and they have many of the attributes of psychopaths. I recommend avoiding them.

Here's another complication. The favorite hormone of one-half of the human race is a potent oxytocin inhibitor: testosterone. In experiments where I have administered testosterone to men, these alpha males are both more selfish and more entitled than their nonalpha selves. Just drink that in for a second. If I raise your testosterone, I can turn you into a teenage boy: living in the moment, taking risks, the future be damned.

For high-testosterone guys (and it's mostly guys, they have 10 times more testosterone than women, though the occasional woman is caught in our testosterone net, too), it's all about them. Their brains are saying "Hey baby, my genes rock, come mate with me."

And it gets more complicated. For every experiment I've run, women release more oxytocin than men do and they are consequently more generous, more trustworthy, and more empathic. This is a major reason why women are nicer than men and connect more easily to others. Women crying at the movies? Yup, that's oxytocin, too.

Another complication: when women are ovulating they become oxytocin sponges, increasing the number of receptors for the molecule and thereby multiplying its effect. Women are more likely to have amorous adventures during ovulation, both with their partners and with other women's partners.

That clever imp evolution didn't make this connection system static. Testosterone tunes itself to our social environment: the winning quarterback certainly gets a hit of it, and so does the president of the chess club when she wins a tournament. But in males, testosterone falls starting in middle age. It also falls when a guy is in a committed relationship and falls further if that relationship produces children. If you are married with two kids at home like me, you have to fight hard not to feel like you're turning into a "girly man." Wash the dishes tonight? Yes, dear. Lower testosterone lets oxytocin's effects blossom and we nurture our offspring just when they need it most.

Our brains are awash in a sea of hormones. Really, our brains are a three-pound gland. Is it any wonder love still baffles us? But, here's some news you can use: Don't look for the perfect partner. Look for someone who wants to trade oxytocin with you. Once that free trade gets flowing, it doesn't take too much work to keep it flowing.

As for my stalker, she didn't see that the oxytocin trade wasn't happening. Sometimes love sucks. Sex is fun, but trading oxytocin forms the connection that can make love last a lifetime.