Why do humans have fingerprints?

The intuitive explanation, that ridges improve grip the way tire tread does, has not held up well. A widely cited study measuring friction between fingertips and smooth acrylic found that ridges reduced contact area and therefore friction compared with flat skin, the opposite of the prediction. Tread works on tires by channeling water on a rough road, which is a different mechanical problem from a soft fingertip on a smooth surface.

Two better-supported functions have emerged. Ridges appear to amplify tactile sensitivity: as a finger moves across a surface, the ridges generate vibrations at frequencies well matched to Pacinian corpuscles, the receptors tuned to fine texture, effectively acting as an antenna for detecting detail. And ridges likely help skin manage deformation and moisture, channeling sweat and allowing the fingertip to stretch and conform without shearing, which may explain why fingers wrinkle in water, itself an active nervous-system response rather than passive swelling, and one that has been shown to improve grip on wet objects. Fingerprints form in the womb by about the 17th week from the interaction of skin layer growth and local pressures, which is why identical twins with identical DNA have different prints. Koalas, remarkably, have prints nearly indistinguishable from human ones under a microscope, an independent evolution of the same solution.