MadSci Network: Anatomy

Re: What's the use of fingerprints?

Date: Wed Oct 3 22:45:04 2001
Posted By: William Beaty, Electrical Engineer / Physics explainer
Area of science: Anatomy
ID: 998768031.An

I read an article about this long ago (probably in Science News), but I don't have the reference.

Fingerprints are part of the mechanism which lets us determine the surface texture of objects. The tiny fingerprint ridges move up and down as your finger strokes a textured surface, and this sends a complicated high-frequency signal to the tactile sensors in your skin. Surfaces with various kinds of roughness will create different kinds of skin vibration when your fingerprint ridges stroke them. In other words, fingerprints act like an "AC modulator" or data encoder which translates a constant stroking motion into rich data signal for your brain to interpret.

This gives a good reason for "whorls" and other fingerprint patterns. Fingerprints only work right when they stroke a surface crosswise. If the fingerprint ridges move parallel to a textured surface, they won't wiggle your skin. An effective fingerprint should have parallel ridges, but should also have patches of ridges will all sorts of orientations so that some of the patches will always vibrate regardless of how you move your finger.

Try this: get some thin plastic wrap, then push one finger through it so the wrap tears and your finger is left with a stretched thin plastic coating. Now rub your finger on various surfaces. You'll notice that the smooth plastic greatly interferes with your ability to feel textures. The same would happen if you burn your fingerprints off with chemicals. The plastic layer doesn't stop you from touching things, instead it presents a smooth polished surface which lacks the signal-producing ridges of normal fingerprints.

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