Scientists Were Wrong About Why Our Fingers Prune in the Bath

Turns out, our shriveled digits serve an evolutionary purpose.

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Prepare to have your world turned upside down: For the longest time, scientists believed our appendages wrinkled underwater because of osmosis, but this may not be the case after all. The old theory was that water washed away the layer of sebum that coats the skin, before passing into the outer layer of the skin and flushing out a handful of compounds found in the skin of the hands and feet, leaving an expanse of parched, pruney skin in their place. But relatively new research proposes a superpower-esque explanation for why our digits morph into old prunes when wet: Wrinkled fingers and toes improve our grip on wet or submerged objects.

The study, which was published in Biology Letters, had participants pick up dry and wet objects with dry hands, then hands that had been wrinkled after soaking in warm water for 30 minutes. The subjects were able to pick up wet objects much quicker and easier with wrinkled hands than they were with dry ones, which points to the wrinkling being an involuntary reaction by the body’s autonomic nervous system—the system that also controls breathing, heart rate and perspiration—rather than just waterlogged skin. The distinctive wrinkling is physically caused by blood vessels constricting below the skin.

“We have shown that wrinkled fingers give a better grip in wet conditions—it could be working like treads on your car tires, which allow more of the tire to be in contact with the road and gives you a better grip,” Tom Smulders, an evolutionary biologist at Newcastle University, UK, and a co-author of the paper, told Scientific American.

This study wasn’t a one-off, either: In 2011, evolutionary neurobiologists Mark Changizi suggested that the pruning must have an evolutionary function. During their research, his team showed that the pattern of wrinkling appeared to provide a drainage network that improved our ability grip things underwater.

Wrinkled fingers, it seems, could have really helped our ancestors gather food from wet vegetation or streams, and wrinkled toes could have help them have better footing in the rain. Unfortunately for our modern selves, however, bars of soap have somehow managed to sidestep this evolutionary miracle. *Sigh*