Fingerprint

Lore & Background

Fingerprints are impressions left on surfaces by the friction ridges on the finger of a human. Moisture and grease on a finger result in fingerprints on surfaces such as glass or metal. Deliberate impressions of entire fingerprints can be obtained by ink or other substances transferred from the peaks of friction ridges on the skin to a smooth surface such as paper. Fingerprint records normally contain impressions from the pad on the last joint of fingers and thumbs, though fingerprint cards also typically record portions of lower joint areas of the fingers. The composition of fingerprints consists of water (95–99%), as well as organic and inorganic constituents. The organic component is made up of amino acids, proteins, glucose, lactase, urea, pyruvate, fatty acids and sterols. Inorganic ions such as chloride, sodium, potassium and iron are also present. Other contaminants such as oils found in cosmetics, drugs and their metabolites and food residues may be found in fingerprint residues. A friction ridge is a raised portion of the epidermis on the digits, the palm of the hand or the sole of the foot. These unique features are formed at around the 15th week of fetal development and remain until after death, when decomposition begins. These epidermal ridges serve to amplify vibrations triggered when fingertips brush across an uneven surface, better transmitting signals to sensory nerves involved in fine texture perception.

Reader's Guide

Fingerprints are among the most widely used and most reliable biometric techniques. They may be employed by police or other authorities to identify individuals who wish to conceal their identity, or to identify people who are incapacitated or dead and thus unable to identify themselves, as in the aftermath of a natural disaster. Their use as evidence has been challenged by academics, judges and the media. There are no uniform standards for point-counting methods, and academics have argued that the error rate in matching fingerprints has not been adequately studied and that fingerprint evidence has no secure statistical foundation. Research has been conducted into whether experts can objectively focus on feature information in fingerprints without being misled by extraneous information, such as context. The determination of fingerprint inheritance is made difficult by the vast diversity of phenotypes. Classification of a specific pattern is often subjective, which complicates analysis of dermatoglyphic patterns. Before computerization, manual filing systems were used in large fingerprint repositories. A fingerprint classification system groups fingerprints according to their characteristics and helps in the matching of a fingerprint against a large database of fingerprints.

Did You Know?

• Fingerprints are formed at around the 15th week of fetal development and remain until after death, when decomposition begins.
• The composition of fingerprints consists of 95–99% water, along with organic and inorganic constituents.
• Fingerprint patterns between monozygotic twins are very similar but not identical.
• There are no uniform standards for point-counting methods in fingerprint matching.