“Aside from a built-in timer to get out of the bathtub, the ability for hands and feet to wrinkle after prolonged exposure to water may confer additional (and much more useful) evolutionary advantage. Research suggests that wrinkled palmar and plantar surfaces act as “tire treads” and allow for heightened grip in wet environments.

This function would have been useful to our ancestors, who may have spent a considerable amount of time in the water, trying to grasp fish for dinner. In a controlled experiment, the group that had soaked their hands prior to the experiment, resulting in wrinkled fingers, were able to perform underwater dexterity tasks more efficiently than the group that did not have.

Though the constriction of the skin in wet environments was previously thought to be the result of osmosis, it is now understood to be a function of the autonomic nervous system: the system responsible for involuntary functions such as digestion, breathing, and heart rate. Individuals with nerve damage to the hands and feet are often incapable of getting wrinkly skin in response to water.

The obvious question then becomes: “Why don’t we always have wrinkled hands?” Scientists hypothesize that the reduction in fingertip sensitivity when wrinkled is too costly, and the ability to adjust based on environment is a much better advantage.”

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http://rsbl.royalsocietypublishing.org/content/9/2/20120999.full.pdf+html

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