Why do we have fingerprints?

February 11, 2017 / Humans / 0 Comments /

Fingerprints regularly come up in crime films and are used to identify suspects at a crime scene. Identifying individuals by fingerprints is a very recent development though. During our long evolution you can be sure that our fingerprints were not used for this, which begs the question – what were they for? There has been some research into the purpose of the fingerprints, and although no one can say for sure what purpose they served during out time as hunter-gatherers, there are some good theories.

 

Why we have fingerprints

Aside from being on our toes, fingerprints are unique to fingers, and are particularly prominent towards the end of our fingers. The role of the fingerprints therefore, must be related to the role of our hands (and toes). This takes you to the next logical step of them helping to grip or hold things.

 

Improving grip – tyre treads

The idea that our fingerprints acted like the treads on tyres or the soles of running trainers was a long standing theory. It makes a lot of sense, and we know that ridges similar to that of our fingerprints do improve grip of tyres on the road, and trainers of tracks. However, this theory was disproved in 2009 by a study published in the Journal of Experimental biology which tested the frictional force of fingerprints. If this theory was true, then fingerprints should increase the friction against a surface, however, this study found the opposite. The reason for fingerprints not improving grip this way is because they are flexible and elastic, whereas car tyres are hard. If our fingers were harder, then fingerprints would probably improve grip. However, this is not the case.

A related theory suggests that fingerprints help drain water away, which would help improve grip on objects by allowing better contact (and so increased friction) between the skin and the object we are gripping. This is somewhat related to why our fingers go wrinkly in water, and although quite possible, it is not known for sure.

 

Improving grip – elastic grip

Although fingerprints don’t help us grip in the obvious way, they may still help grip. The ridges of our fingerprints allow our fingers to stretch easier and behave more elastic. In being stretchy like this fingers can grip rough or moving object better than if they were ridgid. This elasticity can also help prevent damage to fingers by allowing them to stretch rather than rip. This allows is to grip objects that are moving or have some force applied without damaging ourselves. You can see how this elasticity relates to grip yourself by gently holding a cup/ glass in the finger tips of one hand, and moving the cup/ glass up and down with the other. The fingertips in the gripping hand will comfortable move with the glass without ripping the skin, and will maintain a surprisingly good grip still.

 

Sensitivity

There is also evidence to suggest that the ridges which make up fingerprints play a role in our identifying textures and fine details on objects. When fingers run across a surface the ridges that make up fingertips vibrate as they drag and spring back into position. This vibration is picked up by specially adapted nerve cells called pacinian corpusclesThis vibration information passes onto the brain and in conjunction with other nerves, helps to build up an accurate picture of the fine details of the texture of the object.

 

Why are fingerprints unique?

As fingerprints are well known to be unique to the individual, could it have something to do with their function?

The unique nature of fingerprints is largely down to genetics. With everyone having unique genetics, it isn’t surprising that everyone has unique fingerprints in the same way we have unique facial features too. Fingerprints do go beyond genetics though. Genetically identical twins have similar fingerprints, but they are different. When in the womb, if the fetus touches the womb wall it develops ‘friction ridges‘ which, which develop into fingerprints. As no two fetus can can touch the womb wall in the same way at the same time, the ridges do form differently.

 

Summary

Although there is still some debate as to why we have fingerprints, the research done on fingerprints does paint quite a good picture. Fingerprints help you to grip objects, and maintain a strong grip even if an object is moving. You can see how this would be useful as a hunter gatherer when you are trying to hold down some prey, weight a weapon (which, as you wield will try and slip out of your hand) and even building things. The success of humans is our hands and our ability to utilise tools effectively.

Another interesting feature of fingerprints is how they increase the sensitivity of our touch to pick out fine detail in objects. Although there is no clear scenario where this is beneficial, it is certainly an interesting feature.

Image courtesy of Phixaakh


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.