Most people will have noticed that if you stay in a body of water for any extended period of time, your fingertips will go wrinkly. You may have even noticed your toes doing the same, but it doesn’t happen anywhere else on your body – ever wondered why?
Originally, it was thought our fingers went wrinkly because the outer layer of skin (which is made up of dead cells) absorbed water when we were submerged in water for any length of time. The absorbing of water like this would increase the volume of the outer layer of skin, but its can’t just expand out as a sponge would, because it is firmly attached to the underlying layers of skin. So, instead it would wrinkle, which increases its surface area and allows for the expanding surface layer. However, this is not the case.
When we are submersed in a body of water for any length of time, nerves in our fingertips trigger vasoconstriction. It is possible that the nerves are triggered by the water being absorbed by the outer layer of skin, but we don’t know for sure.
This vasoconstriction reduces the volume of the padding in finger tips and toes. You can feel this padding simply by gently pressing your finger tips with other fingers. This padding is essential for our fingers and toes and offers protection for everyday scrapes.The surface area of the finger tips stays the same, so when the volume decreases, the skin wrinkles. It is the same thing that happens to fruit when you dehydrate it. A grape is nice a smooth all around, like our plump little finger tips, but if you dehydrate a grape, it turns into a wrinkly little raisin. This is because all of the water, which makes up most of the volume in the grape has gone, and so the skin is forces to go wrinkly.
This is quite an interesting thing to happen – rather than it being an involuntary thing that just happens when we go into water, the body actively causes this to happen, which suggests there is a reason…..
And there is! Research has shown that wrinkly fingertips are very good at gripping wet objects, and they do this because the wrinkles create channels that allow water to drain away as we press our fingertips on to wet surfaces. This allows the fingers to make greater contact with a wet surface, giving them a better grip.
Being able to grip wet things in water has a clear advantage – it will allow is to climb out of water easier, hold weapons easier, or even keep hold of wriggling food we have just caught.
So, getting wrinkly fingers when we are in the water is not some bizarre result of our skin absorbing water, but rather, it is a very clever evolutionary trait which allows us to grip things better when wet. It is a fascinating evolutionary adaptation, and not one anyone would have thought about. For this small adaptation to be significant, you would think that we would have evolved in a much more aquatic environment than deep inland, and perhaps this offers a small insight into how our evolutionary ancestors lived – perhaps we evolved on or around the coast after all….
Image courtesy of Nicole Hanusek
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Blood vessels constrict, which reduces the volume of the padding in our fingers, which causes them to wrinkle. The reason for this adaptation seems to be to improve our grip on wet objects.