To Catch a Thief: The Psychology of Fingerprints

A psychologists' research showing that no two people have the same fingerprints gives law enforcement a highly reliable way to identify people who don't want to be identified.

Findings

In the late 1800s some mathematically-inclined psychologists became obsessed with measurement. One such psychologist was Sir Francis Galton. Galton took physical measurements of people all over the world, measured the heights of hundreds of British schoolchildren (and their parents), recorded and analyzed weather patterns, and conducted the first systematic studies of the shared traits of identical twins. He also spent a lot of time trying to develop simple tests that would tell him something about a person's race or intelligence. (He usually failed, by the way, and he often did so because his biases about race caused him to test false hypotheses.) In fact, it was Galton's fascination with racial differences that prompted him to take a close look at fingerprints. He had hoped to show that different racial groups had different fingerprints, but his detailed empirical observations did not agree with this hypothesis. However, his studies of fingerprints turned out to have some very important consequences.

Galton came to study fingerprints in a roundabout way. In 1880, a physician named Henry Faulds asked Charles Darwin for some help in documenting some important properties of fingerprints. For example, Faulds suspected but did not know how to demonstrate that no two people have the same fingerprints. Darwin was too old to take on this task, and so he recommended his younger cousin, Francis Galton. Galton took the task very seriously and imparted on a series of empirical studies that allowed him to document not only that no two people have the same fingerprints but also that a person's fingerprints remain largely unchanged over the course of his or her life. While he was at it, Galton also developed the first system for classifying and identifying fingerprints. His book Fingerprints (1892) spelled out his findings.

Significance

Before the ink on Galton's book had dried, law enforcement experts began to realize that Galton's discoveries made it possible to use fingerprints as a highly reliable way to identify people (including people who did not wish to be identified).

Practical Application

In 1892, an Argentine police officer used fingerprints to prove that a woman had murdered her two sons. By 1905, law enforcement agencies in both England and the U.S. began the routine use of fingerprints in criminal investigations. Since that time fingerprint identification has been used for a wide range of reasons (e.g., to identify accident victims, to prevent forged signatures). Without a doubt, however, the science of fingerprinting has been of the most use to law enforcement agents and forensic scientists.

Although advances in DNA testing may make fingerprint evidence less important in the next century than it proved to be in the last, it may be a long time before fingerprint evidence becomes completely obsolete. Even identical twins, whose DNA is indistinguishable, have different fingerprints.

Cited Research

Galton, F. (1892). Fingerprints. London: Macmillan & Co.


American Psychological Association, November 10, 2003