The Brain’s Ways of Dealing With Friends and Strangers; In a new book, Harvard psychologist Joshua Greene shows how different parts of the brain are active in different social situations.

The Brain’s Way Of Dealing With ‘Us’ and ‘Them’

Nov. 22, 2013 7:20 p.m. ET

A tribe of shepherds brings its sheep to graze at a common field. Every shepherd limits the size of his herd to avoid overgrazing the commons—except for one selfish guy who doesn’t care. What should be done to solve this problem? Now consider two rival tribes of shepherds being forced to share the same field. In one tribe, the herd is communally owned, while the second tribe would divide the field into fenced plots belonging to each individual. What should be done to reconcile these two different views?Harvard psychologist Joshua Greene examines these contrasting scenarios in a superb new book, “Moral Tribes: Emotion, Reason and the Gap Between Us and Them.” In it, he explores how dealing with these problems engages very different neural systems.

The first scenario, of the selfish shepherd, is the “tragedy of the commons,” a famed concept in economics. Dr. Greene frames this as the problem of “me versus us,” and in many ways, it’s a simple problem of selfishness within a group, a challenge to its morality. The selfish person rationalizes, “Yes, yes, one shouldn’t do X, we all agree… but here’s why I’m a special case.”

Public space tends to work well when like-minded individuals share it, because they share moral intuitions about how to use it. As reported in the periodical Nature last year, Dr. Greene and colleagues looked at economic game-theory equivalents of the “commons” scenario. Within groups of trusting individuals, the faster someone has to decide something, or the more they have been primed to value intuition over reflection, the more generous and cooperative they are. It requires thought to develop an excuse to stab in the back people whose values you share.

Scenarios that involve a person’s rapid, intuitive bias toward cooperation engage a brain region called the “ventromedial prefrontal cortex,” an area that’s basically an intermediary between the emotional and the reasoning regions of the brain.

A different part of the brain is engaged in the second scenario: a disagreement between a communally-minded tribe of shepherds and an individualistic tribe. Dr. Greene calls this challenge of “us versus them” the “Tragedy of Commonsense Morality.”

In this scenario, both sides can consist of rational, well-intentioned people, but they have different opinions of what common sense requires. Dr. Greene’s crucial point: In contrast to the first scenario, rapid, intuitive decision-making in the second case tends not to lead to cooperation.

When confronted with a group representing “them”—people who don’t share our moral instincts—our guts push us toward xenophobia. We emphasize the seeming self-evidence of our side’s values. In such settings, in Dr. Greene’s words, people “love the language of rights… because it presents our subjective feelings as perceptions of objective facts.” If we resist our automatic mistrustful responses in such circumstances, we engage a brain region called the dorsolateral prefrontal cortex, which is anatomically buffered from receiving impulses from the more emotional parts of our brain.

What we have here is an example of Nobel economist Daniel Kahneman’s distinction between slow and fast thinking. If we’re just dealing with a trusted “us,” it’s best to rapidly feel our way to a moral decision. This isn’t surprising: Humans evolved in groups where nearly all interactions were with familiar people who spoke, dressed, prayed and loved the same way.

But our modern world is full of “thems”—some passing us on the street, others on the far side of a negotiating table, shouting about their rights and sacred values. In that case, beware the rapid gut intuition: “I can’t quite say why, but it’s plain wrong that they do that.” Instead, as Dr. Greene emphasizes, breathe slowly. And think slowly, too.