If a salamander or newt loses its leg, it can just grow another one. Humans aren’t so lucky. If you cut off my arm, it won’t grow back. (Note: please don’t do that.)

But back in the 1970s, scientists showed that children can sometimes regrow the tip of an amputated finger, as long as there’s a bit of nail left over and the wound isn’t stitched up. Later, we discovered that mice have the same ability. But why is the nail important, and why can’t a finger grow back without it? A new study provides an answer to this longstanding mystery. As I wrote in Nature News:

Working with mice, researchers led by Mayumi Ito at New York University