Do Your Fingers Get All Pruney In The Bathtub? Thank Evolution.
You're having a relaxing bubble bath for one when you notice your fingers aging at a rapid pace. Of course they're not actually aging—they're pruning. Why do they always do this? In a 2013 study, scientists announced that they had found the answer. Wrinkly fingers and toes offer us an advantage in wet conditions.
Get A Grip
First off, let's get one thing straight: your fingers don't prune as a result of water seeping into your skin. According to Nature Research, scientists have known since the 1930s that the underwater wrinkling is controlled by the autonomic nervous system—that is, it's involuntary, caused by blood vessels beneath the skin constricting. In fact, it doesn't even happen to people who have nerve damage in their fingers. Still, we've never known exactly why it happens. In a 2013 study published in the journal Biology Letters, researchers sought to uncover that mystery. Their work would piggyback on the 2011 publication of evolutionary neurobiologist Mark Changizi and his colleagues, who suspected that the wrinkles were "optimized for providing a drainage network that improved grip." They couldn't actually prove it at that point, but the 2013 study finally could. The researchers had half of their participants soak their fingers in water, then had all of them attempt to pick up both wet and dry marbles. They found that pruney fingers were better at picking up wet objects, but not at picking up dry ones.
Changizi explains to Nature Research that "pruney fingers are rain treads." Our ancestors likely needed help catching food in wet conditions, and their wrinkly toes helped with footing. As far as they know, other animals who would also benefit from this type of underwater grip likely share this advantage, including macaques.
Why Aren't We Always Pruney?
Here's one thing still puzzling researchers: if wrinkling improves our grip in both dry and wet conditions, then why don't we have perma-pruney fingers? The current hypothesis is that wrinkling could also diminish our fingertips' sensitivity, thus increasing our risk of damage. We'll stick to spidey grip in the bathtub, thank you very much.