The smooth skin of human hands and feet becomes furrowed after extended periods in water. Though often assumed to be a result of water passively seeping into the skin, the phenomenon is actually caused by the nervous system constricting blood vessels. As early as the 1930s, surgeons noticed that no wrinkling occurred if a finger nerve had been severed, so furrowing has been used as a medical indicator of nerve function. But what evolutionary purpose wrinkling serves, if any, remained a mystery.I had heard the water entry explanation before, and it never made sense to me; shouldn't added fluid make your fingers swell up like when they are injured, not get wrinkled? Prunes and raisins get wrinkly when the dry. And since we learned in the 1930s that this was actually a nervous system response, how come nobody ever told me?
Since the wrinkling is something your body does on purpose, why does it do that? Some scientists have now hypothesized that the wrinkles form because the added roughness helps us to manipulate wet objects. They had volunteers move wet objects around before and after soaking their hands in water for 30 minutes, and the resulting wrinkles did indeed help them move the wet objects more quickly. Interesting.