Wet fingers and toes eventually wrinkle, and this is commonly
attributed by lay opinion to local osmotic reactions. However,
nearly a century ago surgeons observed that no wrinkling
occurs if a nerve to the finger has been cut. Here we
provide evidence that, rather than being an accidental side
effect of wetness, wet-induced wrinkles have been selected
to enhance grip in wet conditions. We show that their morphology
has the signature properties of drainage networks,
enabling efficient removal of water from the gripped surface