In a hospital emergency room, five critically ill patients desperately need organ transplants. A healthy man walks in. Should the doctors remove his organs to save the sick five? Most people will respond in milliseconds with a resounding “No way”. Now imagine an out-of-control train about to run down five workers standing on the track. There’s a fork ahead, and throwing a switch could divert the train to another line on which there is only one worker. It’s the same question – should we sacrifice the one to spare the other five? – yet most of us would say “yes” just as quickly.