Why are everyone's fingerprints unique

A. As we all know, the bottom of our hands and our feet, including fingers and toes, are covered

by distinct alternating ridges and grooves that together constitute dermatoglyphics. Fingerprints are just one of these, and toe prints, palm prints and sole prints are just as distinctive and unique as those on our fingers. The ridges follow variable courses, but their arrangement in specific areas has a consistent structural plan. We aren't the only species to have such prints, however. All primates share this anatomical feature.

Q. Why do we have them

A. They act as an aid to tactile sensitivity as well helping us to grip things. A smooth hand would be a much less useful tool.

Q. Why are yours unique to you

A. Everything about your body is unique to you, and no two organs are identical. Nature just isn't that precise. Within a basic pattern predetermined by our genes each physical part of each one of us forms in a way that is slightly different from anyone else who has ever lived, in the same way that each of use has a unique psychological make-up.

With fingerprints - or any other print - no two fingers on the same hand - or foot - have an identical print. Neither do identical twins share the same fingerprints, despite every suggestion to the contrary.

Q. What forms do they take

A. The British scientists Henry Faulds and William James Herschel were the first to describe in print the uniqueness and permanence of fingerprints in an article in the scientific journal Nature in 1880. Their observations were experimentally verified by another British scientist Sir Francis Galton, who suggested the first elementary system for classifying fingerprints based on grouping the patterns into arches, loops and whorls.

This has now been refined, and the FBI now recognises eight different types of patterns: radial loop, ulnar loop, double loop, central pocket loop, plain arch, tented arch, plain whorl and accidental.

Whorls are usually circular or spiral in shape; arches have a moundlike contour, while tented arches have a pointed appearance in the centre; loops have concentric hairpin ridges and are described as 'radial' or 'ulnar' to denote their slopes. Loops constitute about 65 per cent of the total fingerprint patterns, whorls about 30 percent and arches and tented arches together account for the rest. The most common pattern is the ulnar loop.

Q. How long have fingerprints been used for identification

A. Known as dactyloscopy, a system of identification was developed from the work of Sir Francis Galton by Sir Edward R. Henry, who later became chief commissioner of the Metropolitan Police. The Galton-Henry system of fingerprint classification, first published in June 1900, was officially taken on by Scotland Yard in 1901 and quickly became the basis for its criminal-identification records. The system was adopted immediately in most English-speaking countries and is still the most widely used method of fingerprint classification.

A different system of fingerprint classification was devised by the Argentinian Juan Vucetich in 1888. First published in book form in 1904, this system is still used in most Spanish-speaking countries.

Q. What other forms of 'fingerprinting' are there

A. Other fingerprinting techniques have been developed, including the use of a sound spectrograph - a device that depicts vocal variables such as frequency, duration and intensity - to produce voiceprints. More recently, DNA fingerprinting has become more widely used. Analysing those regions of DNA that vary among individuals it is the most accurate method of identification we currently have, and information can be derived from the smallest samples of skin, blood, hair or any other part or secretion of the body.

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By Simon Smith