Everyone is born with one, but no one knows what it’s for. The human appendix is a small dead-end tube connected to the cecum, or ascending colon, one section of the large intestine. Everyone lives happily with it until it becomes painfully inflamed, when the only treatment is to remove it surgically. Then everyone lives happily without it. So why is it there in the first place? Some experts have guessed that it is a vestige of the evolutionary development of some other organ, but there is little evidence for an appendix in our evolutionary ancestors. Few mammals have any...