Say there's a group of five people standing on a train track, and you're on a train coming toward them. You can save the whole group by pulling a lever and switching to another track, but the catch is that you'll kill another person who's standing on that other track. Do you pull the lever?
According to Harvard scientist Mark Hauser, who posed this question to hundreds of thousands of people on the Internet, nine out of 10 people say yes, they would pull the lever. But then, the questions get harder—and the answers much more confusing. It turns out that different parts of our brains make different moral decisions. (11 minutes)
This story originally aired on the public radio program Radiolab.