Fingerprints have been used as a unique identifier for over 100 years — and chances are you've had your fingerprints inked or scanned recently. But who invented this process? Turns out that's the subject of a massive feud — which helped provide useful insights that benefited all of us.

Top image: Photo by Charlie Jane Anders

It started in the 1870s when William Herschel, a magistrate in India, was sick of people signing confessions or testimonies and then claiming that the scrawl on the document wasn't their signature. He had them start putting their fingerprints next to their signatures. This wasn't a physical technique - it was a psychological one. He wanted suspects and witnesses to feel that it wasn't possible to deny that they'd signed a document. After some time, he noticed how unique the prints were. He collected and organized prints, collecting them from the same people again and again for about twenty years. By examining the lot, he determined that fingerprints remained the same for life.

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In 1888, Francis Galton, cousin to Charles Darwin, happened to be proofing some work about the positive identification of criminals when he realized that fingerprint ridges might be the key to an immutable proof of identity. After hearing about Herschel's work, he asked Herschel for his records. Galton planned to used it to set up a system of classification — points that could be checked in order to prove two sets of fingerprints were identical. For four years Galton worked on this system. In 1892, he produced a book, Fingerprints, which revolutionized forensic science, and credited Herschel.

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Then the unpleasantness began.

The same year that Galton contacted Herschel, he had been contacted someone else. The contact came indirectly, through his famous cousin. Henry Fauld's descriptions of fingerprints as permanent identifiers of criminals were easier to dismiss than Herschel's. Fauld certainly had come up with the idea on his own. He'd thought of it while in Japan, admiring ancient pottery. He found the impressions of finger ridges still clear on the old clay. By examining the pot, he could tell that the fingers shaping one part were the same as the ones shaping another part - and that they were all different from his own. Still, he didn't have the massive amount of data to back up his ideas.

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The data he did have might not have encouraged Galton to work with him. Faulds performed experiments on his own fingers, attempting to change his prints with acid, heat, and other painful substances. He, too, determined that fingerprints were immutable. Other people believed him. He even managed to clear the name of an innocent man who was under suspicion of burglary using fingerprints. Faulds had published a paper on fingerprints in 1880, and had since been attempting to raise publicity for his idea. The Darwin letter was one of those attempts. He received no reply, but when he saw, in 1892, that Galton had written a book on the subject he himself had written him about, it was on.

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The feud between them outlasted both their lives. People still debate over who deserves the most credit for the science of fingerprinting - Galton, Herschel, or Faulds. Who do you think deserves the kudos?

[Via Every Contact Leaves a Trace, Scientific Feuds.]

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