Why do fingers wrinkle in water?

For years people assumed pruney fingers were caused by skin soaking up water, but the wrinkling is actually controlled by the nervous system: blood vessels beneath the skin constrict, pulling the surface into folds. Evidence for this is that fingers with nerve damage do not wrinkle. Researchers have proposed the wrinkles act like tyre treads, channelling water away to improve grip on wet or submerged objects — a possible evolutionary advantage for handling things in the rain or water.