Evidence explains why we have fingerprints

Fingerprints don’t give primates grip as we once thought, scientists have recently discovered. In fact, they reduce the friction required to grasp smooth surfaces. Now Dr Roland Ennos and a team from the University of Manchester are trying to find out: why do we have fingerprints?

In 1910, Thomas Jennings was on the run from a murder, but he left behind a clue: a sharp fingerprint in the dried paint of the railing outside the house where he committed the crime. Jennings’ fingerprints were first used as evidence in a criminal investigation, and he was convicted of murder in 1911.

Since then, fingerprints have continued to be an important piece of evidence in forensic investigations. These unique identifiers are so well-suited to the task of detecting criminals, that it is almost the reason why they exist. Which brings us to the question: Why do we have fingerprints, and what biological purpose do they serve?

Dr Ennos from the Department of Life Sciences, University of Manchester, said: “I have been thinking about this for many years and have also studied it. I realized that the leather has the nature of rubber so the fingerprint ridges actually reduce the ability to grip.

“Our experiment – using a plastic cup to create a simple machine in the lab – proved me right.”

He added : “What is interesting is that not only primates have fingerprints, but marsupial koalas also have fingerprints. Whereas monkeys in South America have veins on their tails.”

“Then what are those veins for? The hypothesis that I think is relevant is that these animals allow the skin to change, thereby avoiding blistering. That’s why we get blisters on the soft parts of our hands and feet, not on the creases like the palms of our hands or feet.”

“We are now testing this hypothesis, along with two other theories, that fingerprints improve grip on objects with rough surfaces, and they increase skin sensitivity.”

With just a simple machine – consisting of three pieces of pepech glass and the help of his student Peter Warman, Dr. Ennos disproves the long-held notion that fingerprints help primates grasp. They tested Peter’s grip on each finger and thumb at three different widths of the pepech as the machine pulled the shards of pepech down with a weight placed in a plastic cup. They also tested their ability to grip at three different angles by flexing their fingers and thumbs. This variable study conditions allowed them to separate the pressure from the contact surface and avoid the factors that cause the experiment to fail.

The team published their results in the Journal of Experimental Biology in June 2009. They found that rubbing increased with surface area, which is contrary to the usual rules of physics. assume that rubbing does not change with surface area. That’s because leather is rubbery and not a normal solid.

Evidence explains why we have fingerprints

The team also determined the area of contact by covering the finger and thumb with ink, then taking fingerprints with different pressures. This shows that fingerprints reduce the contact area by 1/3 compared to smooth skin, thereby reducing rubbing.

The results show that the tip of the finger is more like rubber than a regular solid, its coefficients of friction are reduced for strong forces, and the coefficient of friction is higher when the finger is laid flatter. on wider slabs, so the contact area is also larger. The strain pressure is also greater at higher pressure, which indicates the presence of a biofilm between the skin and the surface.

Fingerprints reduce the contact area by 1/3 compared to smooth skin, but it reduces rubbing. This has raised doubts about their supporting function. Dr Ennos said: ‘The experiment was so simple, that discovery should have been made 100 years ago, but scientists make assumptions and seem to have looked at complicated angles. than”.

“I tend to think differently, I am interested in why questions and looking at things that influence people in their daily lives. Everyone thinks that science is all about the impossible, but that is not the case. Science helps us understand the world around us.”

“There are also some side benefits to this job,” he added. For example, some people with nerve damage that inhibits sweating have slippery fingers that can’t be grasped. We can develop a device to treat this disease.”

He and his team will conduct experiments to see how fingerprints affect grip on rough surfaces and on wet surfaces, to see if it functions. is to move water to another place thanks to the grooves on the hand or not. They will also conduct experiments to see if fingerprints help prevent blistering, and if so, how.


‘Fingerprints are Unlikely to Increase the Friction of Primate Finger Pads,’ Journal of Experimental Biology