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human nature: Science, technology, and life.

Mind Makes RightBrain damage, evolution, and the future of morality.

By William Saletan
Posted Saturday, March 31, 2007, at 8:35 AM ET

Imagine that killers have invaded your neighborhood. They're in your house, and you and your neighbors are hiding in the cellar. Your baby starts to cry. If you had to press your hand over the baby's face till it stopped fighting—if you had to smother it to save everyone else—would you do it?

If you're normal, you wouldn't, according to a study published last week in Nature. But if part of your brain were damaged—the ventromedial prefrontal cortex—you would. In the study, people were given hypothetical dilemmas: Would you throw a fatally injured person off a lifeboat to save everyone else? Would you kill a healthy hostage? Most normal people said no. Most people with VMPC damage said yes.

It's easy to dismiss the damaged people as freaks. But the study isn't really about them. It's about us. Neuroscience is discovering that the brain isn't a single organ. It's an assembly of modules that sometimes cooperate and sometimes compete. If you often feel as though two parts of your brain are fighting it out, that's because, in fact, they are.

Some of those fights are about morality. Maybe abortion grosses you out, but you'd rather keep it safe and legal. Or maybe homosexuality sounds icky, but you figure it's nobody's business. Emotion tells you one thing; reason tells you another. Often, the reasoning side makes calculations: Letting old people die is tragic, but medical dollars are better spent on saving kids. Throwing the wounded guy off the lifeboat feels bad, but if it will save everyone else, do it.

Philosophers have a name for this calculating logic: utilitarianism. They've been debating it for 200 years. Some says it's sensible; others say it's ruthless. Lately, however, the debate has been overrun by neuroscience. According to the neuroscientists, philosophers on both sides are wrong, because morality doesn't come from God or transcendent reason. It comes from the brain.

Three years ago in the journal Neuron, the neuroscientists illustrated their point. Using brain scans, they showed that utilitarian decisions involved "increased activity in brain regions associated with cognitive control." From this and other data, they surmised that the moral debate "reflects an underlying tension between competing subsystems in the brain." On one side are "the social-emotional responses that we've inherited from our primate ancestors." On the other side is a utilitarian calculus "made possible by the more recently evolved structures in the frontal lobes." The war of ideas is a war of neurons.

That's where the new study comes in. The idea was to find out what happens when the emotional side, through the VMPC, gets knocked out. As predicted, calculation takes over. Take a kidney? Kill your son? Push a guy in front of a trolley? If it'll save more lives, sure.

Some of the study's authors think this finding vindicates emotions. Since people with VMPC damage are "abnormally 'utilitarian,' " they argue, emotions are necessary to produce "normal judgments of right and wrong." In fact, the authors add, "By showing that humans are neurologically unfit for strict utilitarian thinking, the study suggests that neuroscience may be able to test different philosophies for compatibility with human nature."