Why Your Hands Prune: A Story of Evolution and Tires
If you have ever gone swimming or taken a long bath, you have likely noticed your hands get pruned. Why does this happen?
How it Happens
Originally it was believed that this effect was caused by the absorption of water into the skin. We used to think this caused the surface area of our skin to increase, forming the pruned look of our skin. It turns out, however, that this is not what caused the effect, and the real reason may be far more intentional and an impressive feat of evolution.
Our current understanding of this phenomenon is that as we submerse ourselves in water, our nervous system tells our body to shrink the blood vessels in areas like our fingertips and toes. This shrinking of the blood vessels causes the pruning effect. While this tells us the mechanism of action, it does not really explain why our body developed this rather odd ability.
At first thought, it may seem as though our body does this to conserve heat by focusing blood flow more toward the center of the body and vital organs as opposed to our extremities. However, this answer wouldn't check out either.
The true answer would have a lot to do with evolution and even more to do with tires.
The Curious Connection to Modern Tires
If you want your tire to have the most grip against a dry road, you want the most possible surface area. This means none of the grooves you see on today's tires. This is what you will see if you watch F1 cars racing in dry conditions. However, these tires have one critical downfall. As soon as you add any water between the road and the tire, the water has nowhere to go and gets trapped between the tire and the road.
Even a tiny layer of water between the road and the tire can cause a near-complete loss of traction. Thankfully in 1908, a man named Frank Seiberling invented the grooved tire. The grooved channels would allow for water to have channels it can travel through, moving it away from the vital contact point where tire meets pavement. The roads have been safer ever since.
How This Connects Back to Your Fingers
Scientists now believe that the pruney texture of wet hands may make use of this same idea to improve our grip in wet conditions. Similar to how the grooves in car tires move water away from the vital contact point, these grooves in our skin work in much the same way.
This is the reason why the grooves only occur when in wet conditions. It also explains why only main contact points get pruned to this degree.
A Curious Case of Evolution
Natural selection is the process in which the most well-adapted organisms from a given species can live longer and produce more offspring. This means that those adaptations are more likely to be passed down to future generations.
This tells us that to develop this ability for our hands to prune it must have been a significant advantage at some point in our evolutionary history. This is backed up by recent research showing that pruned hands can significantly increase our grip on wet objects.
Next time you notice your hands prune up, you can thank evolution for giving you the ability to adapt to wet conditions without losing your grip!
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