08/07/2012 05:05 pm ET Updated Oct 07, 2012

The Moral Molecules: Why We Do the Right Thing in Love and Work

George and Henry are cousins, but their behavior in love and at work couldn't be more different. Here's how they are described by Paul, a person who knows them both well.

"George is a stand-up guy," says Paul. "He gets along well with others and he always looks for the peaceful solution to conflict. He is loyal to his mate and shares in the housework and childrearing. He is a good provider and loves to give to his family and friends."

Henry isn't such a nice guy. Says Paul, "Henry is a loner and a 'player.' He doesn't get along well with his neighbors and he tries to seduce every attractive female that crosses his path. He's been married more times than I can count, and I don't think he's ever going to settle down. And what makes me feel even sadder is he has very little regard for his kids, leaving them as easily has he does the females that no longer interest him."

We all know people like George and Henry. But in this case, George and Henry aren't people; they are voles. These chubby little furry creatures with small eyes and big ears look like characters in a Disney movie and have been studied by scientists to find out why they do what they do. Paul J. Zak is one of the scientists, and he offers some interesting insights in his new book, The Moral Molecule: The Source of Love and Prosperity.

Oxytocin: The Molecule of Attachment Love

In the 1980s a young scientist named Sue Carter wanted to explore how the brain chemistry differed in two flavors of social creatures that were closely related but conducted themselves very differently. She studied prairie voles and their cousin species, meadow voles. Our stand-up guy, George, is a prairie vole, and our loner and player, Henry, is a meadow vole.

Could brain chemistry account for the difference? Carter showed that it's the number of oxytocin receptors lining the "reward" areas of the brain that accounts for how the gregarious and monogamous prairie vole conducts his life, and how his anti-social and unreliable cousin the meadow vole conducts his. Paul Zak's research shows that there is a clear relationship in humans between the release of oxytocin, an ancient molecule found only in mammals, and our desire to act well toward others. Humans aren't prairie voles, but we do share the same "love chemical."

"Just like a good human dad piled up on the couch with the wife and kids, the male prairie vole simply feels good spending time with his mate and his young," says Zak. "And like the guy who gets along with everybody down at the hardware store and the VFW hall, this same male prairie vole gets the warm glow of companionship, rather a feeling of threat, whenever he steps out into the burrow at large."

On the other hand Zak notes that meadow voles lack the oxytocin receptors necessary to pick up on the pleasure signals triggered by social stimuli. "This makes them like the young stud driving a pimped-out Trans Am, with a long string of ex-girlfriends but no real friends; or the neighborhood crank who lives alone and threatens to shoot anyone who steps on his lawn."

Testosterone: The Other Side of the Coin

Though few people may have heard about the hormone oxytocin, everyone has heard of testosterone. "Testosterone will make people do some very strange things," says Zak. "Truth be told, the strange-acting people tend to be men, not women. It's testosterone that prompts male risk taking, male violence, as well as the gender's most characteristic behavior: the reckless pursuit of sex, regardless of consequences."

Testosterone has gotten a bad rap, and men suffer by association. James Dabbs, co-author of Heroes, Rogues and Lovers: Testosterone and Behavior, says, "Since studies on testosterone came out in the 1970s, a curiously conflicting body of myths and misconceptions has grown up around the 'male' hormone, based more in ancient superstition and contemporary sexual politics than scientific fact." It's popular among some people who rail against men and their testosterone-driven ways -- that is, until we need guys who are willing to risk their lives by running into burning buildings to save people or putting their lives on the line to protect women and children from attack.

Zak shows that testosterone blocks the binding of oxytocin to its receptor site, which is one of the reasons that young males, with 10 times the testosterone levels of young women, are less empathic. But empathy isn't always a good thing. Think of the guy in our hunter-gatherer past who has such high levels of empathy that he can't stand to leave his wife and children to go out on the hunt. Or the guy who cares so deeply for those beautiful, wild animals that he can't bring himself to kill them.

It also turns out that those who have the most testosterone are the ones who punish loafers and cheaters. For most of human history, we had to count on others to do their part in keeping the tribe alive and well. It was often the high-testosterone guys who would get on the case of someone who wasn't willing to carry his own weight. These were important qualities in the past, and they remain important qualities in our modern world.

Oxytocin and Testosterone: The Dream Team

Paul Zak offers a wonderful TED talk on trust and morality and discusses the importance of testosterone, oxytocin, and other players in the hormonal symphony of the human race. He says that testosterone specifically interferes with the uptake of oxytocin, producing a damping effect on being caring and feeling. "At first this sounds like nothing but a negative," says Zak. "But by making young males -- the hunters and warriors -- not only faster and stronger but less nice, testosterone also makes them less squeamish about crushing skulls in order to feed and protect the family. Nice is often preferable, but when the job is to kill cute little animals for much-needed food, or to repel invaders trying to take your food (or your children), being overly 'nice' is not so nice."

So let's give thanks to the morality we acquired from oxytocin and testosterone, and to the two kinds of creatures who tend to have more of each: women and men.