Air Date: Week of February 8, 2013

A wrinkled finger after a warm bath. Researchers found that wrinkles improve grip in wet conditions and they argue the puckered skin probably provided an evolutionary advantage to early humans. (Photo: Wikipedia)

Scientists think they have an evolutionary answer to why we get wrinkly fingers and toes after a soak in the tub. Living on Earth’s Annie Sneed reports.

Transcript

SNEED: Hang out in the bathtub too long and your fingers and toes shrivel up like raisins. It’s not obvious why soaking in water results in wrinkles. But now, scientists think they have an evolutionary answer to this apparently useless trait. Back in the 1930s, researchers noticed the fingertips of people with nerve damage in their hands weren't wrinkled after being soaked. They concluded that the nervous system must cause this wrinkling, much as it does other involuntary responses such as breathing or sweating.

Yet for years researchers had no scientific explanation for why this would happen. Now a group of evolutionary biologists at Newcastle University in the UK think they have an explanation. They conducted a study where participants picked up wet and dry objects, such as marbles, either with dry hands, or after steeping their hands in water. The people with wet, wrinkly fingers picked up wet marbles more handily than those with dry fingers. But it made no difference whether hands were wet or dry when picking up dry marbles.

The researchers concluded that wrinkles improved grip in wet conditions. They compared the wrinkles on fingers and toes to treads on a car tire, and argued that they probably provided an evolutionary advantage to early humans. Wrinkled fingertips would have helped them forage and grip in wet vegetation or water. The same goes for toes - wrinkles would have given them better footing on wet ground. Even though we no longer go wading into marshes to gather our food, the adaptation remains. So next time you're soaking in the bathtub, keep one hand wrinkle-free, and give the marbles a try. For Living on Earth, I'm Annie Sneed.

Links

Newcastle University’s Tom Smulders explains the evolutionary reason for bathtub wrinkles on the Guardian