I think we all have some sense that our perception of numbers when applied to things like people killed or money lost is somewhat out of whack. If we hear about three people killed by crocodiles, we might feel a certain sympathetic twinge. But if we then find out that 3000 people were killed by crocodiles, we don’t feel 1000 times worse. And if it’s 30,000 people killed by crocodiles… well, that doesn’t seem much worse than 3000. Our ability to apply numbers to tragedy is skewed.

A recent Discover Magazine (July/August 2011) looks at the work of moral scientist and philosopher Josh Greene. The story comments on this topic.

Another moral quirk is the tendency to value human lives less when more of them are threatened. A few years ago, the nation was riveted by the plight of the little boy thought to have been carried away by a weather balloon, but often we barely register the many victims of foreign wars. Or to use the chilling words often attributed to Stalin (but probably apocryphal), “The death of one man is a tragedy; the death of 1 million is a statistic.”

Green and his cohorts set up a series of experiments where they presented subjects with tricky scenarios where they had to choose between saving one man with certainty, or sacrificing that man to possibly save greater numbers of people. The subjects’ brains were MRI’d while they struggled with these conundrums.

… Greene… observed that as the subjects made their decisions, they tapped a fascinating selection of brain areas: the insula, normally used to manage probability and risk, and the ventral striatum which tracks magnitude. Mammals generally rely on these regions to find food and sex. For instance a squirrel might use them to consider how many nuts are lying on the ground and his odds of grabbing a bunch of them before being chased by dog. “You’d like to think that when Truman was deciding to use nuclear weapons and thinking about how many people would be killed and whether the decision would make the war even worse, some special voice of conscience was informing that decision,” Greene says. “But it seems that for decisions involving numbers and probabilities, we default to a system for figuring out how to find the most nuts.”

That’s an interesting, albeit nutty, hypothesis. In essence, our moral decisions are not purely logical because we simply can’t appreciate the math of these situations. Intellectually, we understand that 40 is four times greater than 10, but morally, we do not.