Why Do Fingers go Wrinkly in Water?

November 3, 2015 / Humans / 0 Comments /
Header image for wrinkly fingers

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.

 

Improved grip

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.

 

Summary

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

This Youtube video will give an overview of the information found on the article tab. If you want to know more about the topic, or want to see where the information came from, have a read of the article after you watch the video.

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.


Why have we Retained Hair on our Heads?

May 20, 2015 / Humans / 0 Comments /
Picture of crazy frizzy hair as supporting media for the article 'why do we only have hair on our heads''.

Very few animals indeed have such a strange hair growth pattern as that of humans. If you imagine any other animal with only hair on their head, you realise that it is unusual (not to mention funny), and is just as unique as a peacock’s tail.

Our entire body is covered in a thin layer of hair, except our head. Sure, some people have more body hair than others, but head hair is by far the thickest on the body, even for those who are hairier than normal (ok, the exception is bald, hairy men, but there are other reasons for this). So why do humans have a lot of hair on their heads, but not much on our body?

 

Heat retention

The head has a large surface area and a large blood supply, which means large amounts of heat are lost through the head. Having hair on your head acts as an insulating layer, which prevents heat loss. The body loses less heat per unit area compared to the head, which is probably why we have lost some of our body hair, but kept head hair. In addition to this, wearing animal skins and clothes on our body would have reduced the need for body hair.

Heat retention is probably the most likely, and important factor for the reason we have head hair, but there are other potential reasons which may have also contributed to some degree.

 

Homoaquaticus

This is a favorite theory of our evolution, and although it is lacking some real evidence. Sometimes referred to as ‘water-ape’, this theory suggests that as early man we grew up by the coast. Here we could hunt for food on land, but also wade out to sea to search for food. Imagine an ape wading out to sea and coming back – they would be dripping wet, and would get cold. So, we evolved to lose our body hair, so we wouldn’t stay wet for so long once out of the water. The hair on our head remained to retain body heat, but also because our heads didn’t really go underwater, because we needed to breath.

Although not an accepted theory of evolution by most people, losing body hair but head hair would offer an advantage to early humans looking for food at sea.

Besides, how else do you explain why humans and sea mammals have a similar bone structure in the flipper and hand? Why would a whale or dolphin need those bones in its hand? Food for thought, but not concluding evidence.

 

Attraction of the opposite sex

Hair decoration to attract a mate has been going on for an incredibly long period of time, and our ancestors have gone to great lengths to gather special gels to make their hair ”attractive”. Ancient bog body discoveries almost always find that the person had gone to a surprising amount of effort to have their hair in a certain way. It is possible that having a good head of hair 3000 years ago would have increased your chances of getting a mate, and passing your hair genes on.

Ok, so 3000 years is not long in terms of evolution, but this does offer a bit of support as to why head hair has endured the test of time so well. This also mirrors this explanation for the purpose of the aforementioned peacock’s tail. potentially more truth here than you think…

 

Summary

The most acceptable, and most probable reason for having hair on our heads and not the rest of the body is to retain heat. We probably lost the matching body hair because we started wearing animal skins/ clothes which made body hair redundant.

It is of course possible that there are other contributing factors which have ensured an advantage to those who are particularly folically gifted; and they may include the ‘water-ape’ theory and using hair as a tool to attract the opposite sex.

Picture courtesy of MorkiRo

This Youtube video will give an overview of the information found on the article tab. If you want to know more about the topic, or want to see where the information came from, have a read of the article after you watch the video.

It is an evolutionary adaptation for the need to keep our heads warm to conserve heat. Clothing meant that we didn’t need body hair so much, so that gradually was lost.