Bertillonage

BERTILLONAGE

Bertillonage, also known as the Bertillon system, was a method of biometric identification based on anthropometry—the precise measurement of the human body. Used widely in the late 19th and early 20th centuries, it combined detailed numerical data (such as head length and breadth, finger and foot lengths, and arm span) with photographs and written descriptions to create a unique profile of each individual. The system was the brainchild of Alphonse Bertillon, a French criminologist devoted to a rigorously quantitative approach. Appalled by the unsystematic way police identified suspects, he reasoned that a set of unchanging physical measurements would be far more reliable than names or aliases: “You can replace your name by an alias, but there’s no alias for the shape of your head.” Adopted by the Paris Prefecture of Police in 1883, bertillonage quickly spread across the globe; at its peak, departments from Bucharest to Buenos Aires maintained “Bertillon cabinets,” which became, in the words of the criminologist Raymond Fosdick, “the distinguishing mark of the modern police organization.”

The Victorian statistician Francis Galton, who had done extensive work with anthropometric data, saw an opportunity to refine the system. He asked whether Bertillon’s choice of measurements was optimal, or if taking more measurements would improve accuracy. Galton realized that bodily measurements are not independent: for example, hand size and foot size tend to vary together. Adding measurements that are highly correlated with ones already recorded yields diminishing returns, because the new numbers add little extra information. To study this, Galton plotted height against cubit (elbow-to-middle-finger) and found the same elliptical scatter pattern he had observed in other correlated pairs. He looked for measurements that added information beyond those already recorded, a question he could investigate using his collection of anatomical data.

In the end, Galton’s statistical critique did not lead to an improved Bertillon system. Instead, he championed a competing method: dactyloscopy, or fingerprinting. Like bertillonage, it reduced a suspect to a set of recordable symbols, but it had the crucial advantage that fingerprints are often left behind at crime scenes, available even when the criminal is not. The case of Vincenzo Peruggia—who stole the Mona Lisa in 1911 and left a print on the discarded frame—made this point vividly. Had the police files contained dactyloscopic records instead of Bertillon cards, Peruggia would have been identified immediately. Thus, bertillonage gave way to fingerprinting, which in turn prefigured modern biometric tools like DNA profiling. Indeed, as Justice Anthony Kennedy noted in the 2013 U.S. Supreme Court case Maryland v. King, a DNA sequence functions much like a twenty-first-century Bertillon card—a set of uniquely identifying data points attached to an individual.