Salamanders regenerate their tails. Sea stars regenerate their arms. Most species of planaria, a type of flatworm, can regenerate everything from their brains to their digestive organs. But if you lose part of a finger in a shop class accident, or while chopping vegetables for dinner, you’re out of luck—for now. “Why can the worm do it, and we cannot?” asks Daniel Lobo, assistant professor of biological sciences. That’s not really the question, though, he explains.