The Shocking Reason Behind Pruney Fingers!

If you’re like me, and were curious as a child, you probably wondered why your fingers and toes pruned up if you spent too long playing in the bath or a swimming pool. Maybe you asked an adult, and maybe they gave you some vague answer involving osmosis, or maybe they didn’t really know why it happened either. The truth is, that question has only had a complete and compelling answer for a few years, and even the current consensus on the matter isn’t universally accepted.

For a long time people thought that it had something to do with osmosis. At first glance, this makes sense. You learn pretty early on in your science classes that two sets of liquids separated by a membrane will attempt to even out in terms of concentration of a solution. So if you’re relaxing in the bathtub and lose track of the time, it might make sense that perhaps the salt inside of your body underwent some sort of osmosis and escaped into the bathwater, leaving your fingers and toes appearing shriveled, almost deflated. Heuristically that answer might be satisfying, but it isn’t without it’s problems.

First of all, if this really does have to do with saltwater osmosis, then why does pruning still happen in the ocean? And secondly, why is it limited to fingers and toes? Wouldn’t that process take place all over the body if it was purely chemical? Well there’s some relatively new evidence that it isn’t purely chemical at all, and in fact has nothing to do with saltwater osmosis.

Often the best way to learn if our assumptions are correct isn’t to continue seeing when things work as predicted, but to discover when they don’t. It all started when people with nerve damage noticed that they didn’t prune on any of their digits affected by the nerve damage. Researchers have known since about the 1930s about this phenomenon, and the implications. This information suggests that the process, rather than chemical, is a reaction by the nervous system.

Because of this, some researchers have deduced that since it is an active process rather than a passive matter of chemistry, then it probably has a reason for being selected for in our evolution. It was only in 2011 that studies were conducted to see if this process offers us any benefits that might have translated to an evolutionary advantage for our ancient ancestors. It turns out that pruney fingers and toes actually offer an significant increase in our ability to grip things. It must have offered enough of an advantaged to be selected for. Perhaps it helped our ancestors hold spears in the water, collect food from wet vegetation, and even remain sure-footed in the rain.

There are even those who believe that humans have an aquatic ape ancestor, accounting for our, among other things, our lack of hair in comparison to our ape relatives. Although this theory might be a bit much to go into today, and, for the record, is much less accepted by the scientific community than these new findings about the benefits of pruney fingers as an active response from the nervous system. Either way, now you have an answer for next time someone asks. Forget saltwater osmosis, you have your nervous system to thank for your temporarily wrinkled fingers.