The Compassionate Instinct

And yet when researchers like Joyce Berg and others have had people play the trust game with real monetary stakes, they have repeatedly found that the average investor will transfer half of her initial endowment and receive similar amounts in return. Through the trust game, researchers have also discovered a number of factors that seem to drive levels of trust. Familiarity breeds trust—players tend to trust each other more with each new game. So does introducing punishments for untrustworthy behavior or even just reminding players of their obligations to each other.

These studies have demonstrated the strength of human trust and that humans are truly worthy of this trust from one another. They have also improved our understanding of the social factors that determine trust. But two important questions remain: Is trust truly a biologically based part of human nature, and if so, what is it in the brain that makes humans trust each other?

BIOLOGY OF TRUST

This question might sound complex, but there is a simple hypothesis about what steers the human brain to trust another human: a hormone called oxytocin.

Oxytocin is produced in the brain’s hypothalamus and stored in the posterior pituitary gland. We know that it helps smooth muscle contractions in childbirth and in breast-feeding mothers. But recently we’ve discovered that its applications go beyond the maternal. It turns out that oxytocin also reduces social anxiety and helps people meet and bond with each other. A man and woman involved in the mating dance are releasing oxytocin; so are friends having a good time at dinner.

Forming relationships like these involves trust, but is there a direct connection between trust and oxytocin?

To find out, my colleagues and I conducted an experiment in which participants took either oxytocin or a placebo. Fifty minutes later, participants played the trust game against four different anonymous partners. They played with real money, with each point worth almost half a Swiss franc.

The results revealed that oxytocin does indeed seem to grease the wheels of trust. Of the 29 investors who had taken oxytocin, 45 percent transferred the maximum amount of 12 points in each interaction. By contrast, only 21 percent of the placebo-group investors did so. The average transfer made by the oxytocin-group investors was 9.6 points, compared with 8.1 points by the placebo-group investors.

Interestingly, the investors’ expectations about the back-transfer from the trustee did not differ between the oxytocin and placebo recipients. Oxytocin increased the participants’ willingness to trust others, but it did not make them more optimistic about another person’s trustworthiness.

The results indicate that oxytocin does indeed somehow help humans overcome distrust. But does oxytocin really increase trust, or does it merely make us feel so good that we lose our aversion to risk and betrayal?

To figure that one out, we conducted a second experiment, in which investors faced the same choices as in the trust game. The investors in this experiment were again in a risky situation, but this time there was no human being on the other side of the table; instead, investors faced a computer that generated random numbers of points. Everything else in the “risk experiment” was identical to the trust experiment.

The result? Investors who’d received oxytocin behaved no differently than those in the placebo groups. We therefore concluded that the effect of oxytocin is, indeed, specific to trusting other people and the willingness to take risks in social situations. Oxytocin does not affect human attitudes toward risk and uncertainty in situations where there are no other human beings involved.

In short, trust is very much a biologically based part of the human condition. It is, in fact, one of the distinguishing features of the human species. An element of trust characterizes almost all human social interactions. When trust is absent, we are, in a sense, dehumanized.

APPLIED TRUST

The discovery that oxytocin increases trust in humans is likely to have important clinical applications for patients suffering from mental disorders like social phobia or autism. Social phobia ranks as the third most common mental health disorder after depression and alcoholism; sufferers are severely impaired during social interactions and are often unable to show even basic forms of trust toward others.

Given the results of our trust studies, the administration of oxytocin, in combination with behavioral therapy, might yield positive effects for the treatment of these patients, particularly in light, too, of its relaxing effects in social situations.