A series of laboratory tests have shown that wrinkles on fingers and toes resulting from water immersion actually improve grip on wet or submerged objects. Think car tires: the grooves on your fingers provide a channel through which water can be evacuated as the part touching the object squeezes fluid out of the way.
In the experiments, subjects had to pick up wet or dry objects—such as marbles—with normal hands or fingers that had been soaked in water for 30 minutes. Those with wrinkly fingers could pick up wet objects faster and more reliably. The research, published in Biology Letters, strongly supports the hypothesis that we evolved the wrinkly-finger-syndrome as an evolved trait.
When tramping around the wet'n'wild outdoors on hunting trips, our forefathers' wrinkly fingers and toes could have helped them gather food: giving them better grip on rudimentary tools soaked from rain, or better foot traction on wet rock surfaces.
So why aren't our fingers permanently winkled? That remains to be discovered—but it could be that smooth fingers offer better sensation or dexterity than the shriveled versions. Regardless, it'll give you something to think about next time you're in the bath. [Biology Letters via Nature]
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