Oxytocin is a neuropeptide that impacts our social interac-tions and ability to trust and cooperate with our peers. When oxytocin is released in the brain, we are more likely to show empathy or altruism—leading Zak to wager that oxytocin is actually responsible for the creation of the modern world.
What’s the mechanism for a molecule changing our emotional state regarding another person?
Oxytocin is a sort of moral governor, and that sense of morality comes from this ancient mechanism that modulated approach and withdrawal behavior. The precursor molecule for oxytocin, which was found in fish at least 400 million years ago, modulated approach and withdrawal behavior between males and females to facilitate sexual reproduction. So the value of sex is that you get greater genetic diversity faster. But the curse of sex, if you’re a fish, is that if this other fish gets close enough to you to fertilize you, you might instead become its lunch. What the precursor oxytocin did in the female was allow the approach of a male fish, but only when the female was ovulating.
Oxytocin does the same thing in humans. It modulates approach and withdrawal behavior, and it does so by modulating fear responses.
Is it significantly different in function in humans and other mammals?
About three percent of mammals are socially monogamous—that is, the males and females live together to raise offspring. And that includes human beings. All mammals have this approach and withdrawal factor that depends on oxytocin. But the three percent of mammals that are socially monogamous get their reward from positive interactions. So among most mammals, the males mate and disappear. But we humans, in particular, mate and mostly stick around.
Not only is this system rare among mammals—this reward for positive interactions system, if you will—in human beings, it’s like in hyperdrive. So not only do human beings interact with their family and friends, and get pleasure from it, they actually interact with complete strangers. And we’re really the only species that does that on a regular basis.
So, my bigger claim is that oxytocin is in fact responsible for the modern world. We’d still be living in caves and little kin-based groups if we didn’t have what looks like a mutation in the oxytocin receptor gene somewhere around 200,000 years ago. All of a sudden, we went from living in groups of 150 to living in groups of 5,000, up to 10,000.
Is that roughly when language evolved as well?
Language was maybe a little bit before that, maybe even up to half a million years ago. But language certainly facilitates this process. Now I don’t even have to know about you; I can just have your reputation sustain cooperation. So the people I interact with say, “Hey, Ben’s a good guy, Bob’s not,” so we ostracize Bob, and Bob either dies and doesn’t reproduce, or Bob goes to some other group.