Not long ago, a friend of mine asked me if I had heard of a condition called situs inversus. He had learned about it when his grandson had been born with his internal organs flipped–heart on the right, liver on the left, and so on. Despite that remarkable reversal, the boy was fine. His story got me curious about how the condition happens–and how our bodies, for the most part, figure out which side is which. The result is a story in tomorrow’s New York Times. Check it out.