A long soak in the tub can wreak havoc on your fingertips, transforming your smooth digits into wrinkly eyesores. But this rumply skin may actually serve a purpose, according to a new study. It helps us get a stronger grip on slippery objects, especially those underwater.
Scientists long thought that wrinkly fingers were caused by osmosis—swelling of the outer layer of the skin as water seeped into cells. But experiments conducted in the past few years—as well as observations that water-induced wrinkles don't form on the tips of previously severed but subsequently reattached fingers—suggest that the wrinkles are instead produced by nerves that automatically trigger constriction of the blood vessels beneath the skin, reducing the volume of the tissues there.
Having something under the direct control of a nerve, even an involuntary one, suggests it serves an evolutionary purpose. But that begged the question of what function finger wrinkles have. In 2011, a team of neuroscientists proposed that the folds improved our grip on wet or submerged objects, just as the treads on tires help improve traction. "That seemed like a clever hypothesis that would be easy to test," says Tom Smulders, an evolutionary biologist at Newcastle University in the United Kingdom.
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