Fingerprints May Help Enhance Grip by Controlling Moisture
(Inside Science) -- Fingerprints are unique to primates and koalas. However, it remains a mystery exactly what evolutionary benefits these ridges provide compared with the smooth pads of carnivores such as cats or bears.
Previous research found the tips of fingers and toes, the palms of hands and the soles of feet possess a much greater density of sweat glands than flat skin, which suggested that fingerprint ridges might deal with moisture in some way. To investigate this possibility, scientists analyzed the behavior of moisture on fingerprints pressed against glass surfaces using infrared, optical, and terahertz and megahertz wave imaging.
The researchers found that when fingertips were dry, they released sweat, which softened the skin, helping fingertips flatten onto surfaces and dramatically increasing the friction they experienced. Such mashing also blocked fingertip sweat pores, preventing them from getting too slippery with perspiration. On the other hand, when fingertips were wet, the fingerprint furrows supported evaporation, removing excess moisture.
All in all, these experiments revealed that regardless of whether fingertips started off wet or dry, they were inclined to possess roughly the same amount of moisture in fingerprint ridges, maximizing the amount of friction between the fingertips and the glass and reducing the chances of a slip.
Prior work found that fingerprint ridges sweat in response to emotional states rather than temperature changes, suggesting they are linked with "fight or flight" reactions instead of helping to cool the body. These new findings suggest fingerprints evolved at least partly to help people and other primates optimize their grip in life-or-death situations, such as climbing up trees or holding onto weapons or tools.
When it comes to developing artificial fingers, these findings suggest "incorporating ridges is important for controlling friction, and hence the grip of wet surfaces," said study co-author Michael Adams, a physicist at the University of Birmingham in England.
The scientists detailed their findings online Nov. 30 in the Proceedings of the National Academy of Sciences.