Now that we've entered the annual season of "goodwill toward men," it seems like an excellent time to consider oxytocin, a hormone that has gotten attention in recent years as the grooviest thing since lava lamps and love beads.
Oxytocin is secreted by the pituitary gland, and it has effects on regions of the body of a type that you memorize for a final exam and then promptly forget. But oxytocin also gets into the brain, where it affects behavior.
How? For starters, oxytocin promotes maternal behavior in rodents. Pump up a new mother mouse with oxytocin and she grooms her infants more. Block a mouse's oxytocin system in the brain with some genetic engineering and she becomes less maternal. In rodent species that form long-term, monogamous pair bonds, oxytocin promotes formation of those bonds.
And oxytocin doesn't just work on rodents: It has all sorts of "pro-social" effects in humans as well. Spritz oxytocin up people's noses (when they don't know if they are getting the hormone or a placebo) and they become more trusting and forgiving. In economic games requiring players to choose whether to cooperate or to be cutthroat, oxytocin promotes cooperation. (And just to show that this is about sociality, oxytocin had no effect on subjects who thought they were playing with a computer instead of a human partner.)
Subjects watching video clips of a supposed politician trusted the person more when given oxytocin. The hormone has been found to make people more charitable — and not just to individuals but to charitable institutions, a more emotionally abstract way of giving money. Scary or angry faces are seen as less so by people under the influence of oxytocin, and the amygdala — a part of the brain that responds to cues that evoke anger or fear — becomes less responsive.
Oxytocin even appears to have some therapeutic potential. In studies on males (who might be said to be genetically impaired in pro-social behavior by virtue of their Y chromosomes), oxytocin was found to increase their capacity for trust, their skill at reading facial expressions and their tendency to make eye contact. And oxytocin fosters sociality in people with autism.
It was enough to make the journal Science, about as staid a publication as there is, lose its cool and allow the phrases "love drug" and "cuddle chemical" in an article on oxytocin's social effects in humans.
But in science, further investigation often has a way of dashing high hopes, and now come three more recent studies.
In a 2010 paper, Carolyn Declerck and colleagues at the University of Antwerp studied oxytocin's effects on participants who played an economic game. Pairs of subjects were introduced and then, over the course of the game, had to decide whether to cooperate or stab the other player in the back. As expected, the hormone made players more cooperative. So far, so good. And in similar work, Carsten De Dreu and colleagues at the University of Amsterdam had people play as members of a team, with a study design that allowed participants to choose to be self-sacrificing for their collective cause. Again, no surprise: Oxytocin increased self-sacrifice.
But there was also bad news for believers in utopian endocrinology. In the Declerck study, if players had not met each other before a game, oxytocin didn't make for cuddly feelings — people were less cooperative and trusting. In the De Dreu study, people playing the economic game as a team were, naturally, playing against another team. And those people who had been spritzed with oxytocin became more preemptively aggressive against the teams they were pitted against, even as they cooperated better with their partners. In another study, De Dreu found that oxytocin caused Dutch subjects to become more ethnocentric and hold more negative unconscious perceptions of Arabs and Germans.
Oxytocin, this research seemed to suggest, makes people feel warmer and fuzzier to those they consider "us." But it makes people crappier to the "thems."
So where does all this leave us? We've now got some fascinating research that shows the power of a hormone to affect behavior. But the findings also demonstrate the even greater power of social context. In one setting, when you see another person's similarity to you, you're likely to feel a responsibility to honor the golden rule, and oxytocin enhances this. But in another context, when what you see in the person standing before you are differences, oxytocin might egg your neurons on to smite him.
It now seems clear that there's no free endocrine lunch. Even if oxytocin is just the thing to bring peace in our time to the rodents of the world, there's no single hormonal switch that can make us better humans.
Robert M. Sapolsky is a professor of neuroscience at Stanford University and the author of "A Primate's Memoir," among other books.