Why Do We Have Fingerprints?

    Many scientists once thought fingerprints help us hold onto objects. From an evolutionary perspective, getting a better grip on tools or weapons would have made life easier for early humans. In 2009, Dr. Roland Ennos of Manchester University designed an experiment that tested the gripping power of our fingerprints. He used a machine equipped with weights to pull strips of Perspex, a kind of acrylic, across a subject’s fingertips. The machine measured the amount of friction created as the acrylic passed over the tip. In the real world, a high amount of friction between two solid objects in contact with each other would indicate a better grip. In the experiment, the fingertips created some friction on the acrylic, but not as much as Ennos had expected.

    Ennos compares our fingerprints to the tires on a race car. Ridges in the tire reduce the surface area of the tire in contact with the road, which reduces friction. The ridges on fingertips have the same effect. Smooth skin has more surface area and so more friction when in contact with an object than fingerprints do. Where fingerprints might provide more grip, Ennos suggested, is when we grab objects with rough surfaces. The ridges on the fingertip extend into the object’s depressions and increase the contact area.

  At almost the same time Ennos was doing his research, a team of French scientists suggested a possibility for why we have fingerprints. They think fingerprints help gather information about objects we touch and send signals about them to the brain via the nervous system. In their study, the scientists outfitted one artificial hand with grooves on its tips to simulate fingerprints. Another robotic hand had smooth “skin.” The hand with the fingerprints was much more sensitive to different surface textures. According to Georges Debrègeas, who helped lead the study, “We believe that fingerprints actlike antennas, amplifying the signal.”

  Other theories about the possible role of fingerprints suggest that they help to divert water and keep our hands dry or that they prevent blisters. To support that second theory, Ennos notes we rarely get blisters on our fingers or the other parts of the body with natural ridges, such as the palms of our hands and the soles of our feet. The ability to pin down what role our fingerprints actually play could help scientists develop more lifelike prosthetic hands.