Scientists have an answer to the pressing question of why hands and feet get wrinkled after too much time in the bath: Pruniness may have evolved to make it easier to handle wet objects.
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.
In 2011, a team of researchers proposed that the grooves in wet fingers might function as “rain treads” that improve grip by channeling water away, much like car tires on a wet road do. Now, researchers at Newcastle University in England have tested that theory.
The researchers had 20 volunteers manipulate objects with smooth fingers or digits shriveled by immersion in warm water for 30 minutes. The experimenters measured how long it took people to transfer the objects between a water-filled container and a dry one, or between two dry ones, with wrinkled versus unwrinkled fingers. The objects were glass marbles and fishing weights of various sizes.
All the participants transferred the wet objects (but not the dry ones) faster when their hands were pruney. The results suggest furrowed fingertips make it easier to handle moist items more efficiently, the scientists report online January 8 in Biology Letters.
