Humans have recognized the unique properties of fingerprints for thousands of years. However, fingerprint analysis didn't become an actual crime-solving forensic science until the early 20th century. In ancient Babylon, for example, clay impressions of fingerprints were used to seal business deals.
Sir William Herschel is recognized as one of the first Europeans to begin collecting and studying fingerprints in the 1850s, which inspired others to do so as well. Since that time, the practical application and study of fingerprints has come a long way.
Dr. Jan Halamek, a professor at the University of Albany in New York, led a research team that came up with a test to determine a person's gender based on their fingerprints. Instead of examining size and shape, Halamek's test examines and analyzes the amino acid compounds in latent prints.
These fingerprints are created by sweat and natural oils, so heating the prints and applying a special chemical dye causes them to turn a specific color based on the concentration of amino acids left behind by the skin. Due to the fact females have more amino acids than males, Halamek claims the test is 99% effective.
Sir Francis Galton, the man who may have coined the term "eugenics," is regarded as something of a fingerprints pioneer. An anthropologist and the cousin of biologist Charles Darwin, Galton was interested in the controversial idea that humans could be selectively bred to achieve desired traits. He theorized a person's fingerprints might be able to identify their racial characteristics or level of intelligence.
Galton's study of fingerprints led him to create a classification system called Galton's Details. The system identifies the raised ridges in a print based on five characteristics: the enclosure, the short ridge, the dot, the ridge ending, and the bifurcation. Modern-day investigators still study these details to determine whether or not two prints are alike.
French criminologist Edmond Locard began studying fingerprints back in 1910. Locard's specialty was poroscopy, which examined not only the ridges of a fingerprint but also the marks left behind by the pores in the skin. Several years later, Locard determined that if 12 points on two fingerprints match each other, then those prints are made by the same finger.
This standard is often used to this day. However, countries' legal systems set different standards for the number of matching points required to conclusively connect two fingerprints.
People leave behind three different types of fingerprints that crime scene investigators look for: patent, latent, and plastic. Patent prints are easily visible and left by substances like blood, ink, dirt, and grease. If someone with a bloody hand touches a solid surface and leaves behind a print, that's a patent print. Latent prints aren't visible at all. They're made of the sweat and oils present on a person's hand. People leave behind latent prints all day long and never think about it. These are the types of prints that are lifted at crime scenes using special powders and brushes.
Plastic prints are three-dimensional. These prints are made in paint, tar, soap, wax, and even clay. When law enforcement or crime scene techs process a crime scene and see patent or plastic prints, they simply take a picture of them, as they do not need to be processed in the same way as latent prints.