Human skin gets pruny—those wrinkled, shrivelled fingers and toes—when it's exposed to water for a long time because of a clever response by your nervous system, not just simple water absorption.
Here's what happens:
When your fingers or toes are in water for a while (especially warm or cold water), nerves in your fingers trigger the blood vessels below the skin to constrict. This causes the upper layers of the skin to pull inward, forming wrinkles.
It used to be thought this happened because water was just soaking into the outer layer of skin and causing it to swell unevenly. But now we know:
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It’s controlled by the autonomic nervous system, the same system that controls things like heart rate and breathing.
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It doesn’t happen if the nerves are damaged, which supports the idea that it’s a nerve-driven process.
Why would evolution give us prune fingers?
The leading theory is that wrinkled fingers improve grip on wet or submerged objects—kind of like the treads on a tire. This would have helped our ancestors gather food or climb in wet conditions.
So basically, pruny fingers might just be your body's way of giving you "rain tread" for your hands and feet!
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