A fingerprint in its narrow sense is an impression left by the friction ridges of a human finger. The recovery of fingerprints from a crime scene is an important method of forensic science. Fingerprints are easily deposited on suitable surfaces (such as glass or metal or polished stone) by the natural secretions of sweat from the eccrine glands that are present in epidermal ridges.
In a wider use of the term, fingerprints are the traces of an impression from the friction ridges of any part of a human or other primate hand. A print from the sole of the foot can also leave an impression of friction ridges.
Deliberate impressions of fingerprints may be formed by ink or other substances transferred from the peaks of friction ridges on the skin to a relatively smooth surface such as a fingerprint card. Fingerprint records normally contain impressions from the pad on the last joint of fingers and thumbs, although fingerprint cards also typically record portions of lower joint areas of the fingers.
Human fingerprints are detailed, unique, difficult to alter, and durable over the life of an individual making them suitable as long-term markers of human identity and may be employed by police or other authorities to identify individuals who wish to conceal their identity, or to identify people are incapacitated or deceased and thus unable to identify themselves, as in the aftermath of a natural disaster. Fingerprint analysis, in use since the early 20th century, has led to many crimes being solved. This means that many criminals consider gloves essential.
How are fingerprints formed in the womb?
An innumerable amount of environmental factors influence the formation of fingerprints, including the exact position of the fetus in the womb at a particular moment and the exact composition and density of surrounding amniotic fluid that's swirling around the fingers as they touch surrounding structures. And that's what decides how every individual ridge will form. The entire development process is so chaotic that, in the entire course of human history, there is virtually no chance of the same exact pattern forming twice.
Unlike most wrinkles on our bodies, which appear due to bending and stretching of the skin, fingerprints aren't the result of repeated motion. Each of us is born with a unique set of them, although scientists aren't exactly sure what purpose fingerprints serve.
One possible purpose of fingerprints is that they improve our sense of touch. In a recent study, scientists have investigated this idea by performing a series of experiments with artificial fingertips made of rubber-like sensors. The scientists compared the sensitivity between these grooved artificial fingertips and a smooth skin-like material, and found that the grooved fingertips produced vibrations up to 100 times stronger than the smooth material when sliding against a slightly rough surface.
The researchers, from the Ecole Normale Superieure in Paris, explained that increased vibrations give us an enhanced sense of touch, especially for detecting textures. As you rub your fingers across a textured surface, your fingerprints specifically amplify vibrations in an optimized frequency range to stimulate the Pacinian corpuscles, which are nerve endings in the skin that detect textures. In turn, texture information allows us to identify objects by touch.
As the finding demonstrates, not only does our nervous system (the "software") play a role in tactile computation, but the physical characteristics of the body (the "hardware") also enhance the computation when sensing.
However, the research doesn't explain why everyone's fingerprints are unique, or why our fingerprints are typically arranged in elliptical swirls. The scientists suggest that the loop design may ensure that some ridges are always brushing perpendicular to a surface, no matter the orientation of the fingertips. In addition, the researchers predict that this work could lead to enhanced tactile feedback for prosthetic hands.
Why do we have fingerprints or ‘prints’ on only our palms and feet? Is there a difference between the types of skins?
The skin on our hands and feet is different. First, we don't have any hair there. Even places on your body that don't seem to have hair usually have short, fine hair. But the soles and palms have none. There are a lot of sweat glands here too.
For another thing, theres less pigment (color). Even people with very dark skin elsewhere usually have pinkish-white palms of their hands and soles of their feet.
The skin is also thicker (about 8-14 times thicker) here, which makes sense since theres so much chance to wear down these areas. The cells here divide sooner, while they are still smaller than skin cells in other places. The differences in color and thickness are because of one gene that makes a protein called DKK1. The body only makes this protein on the palms and soles.
Fingerprints (and footprints) are tiny ridges in the surface part of the skin (epidermis) that are formed by lines in the deep skin (dermis). They probably give us better grip by giving our skin more friction. They may also help keep the skin from tearing easily.
Scientists still haven't figured out why the patterns are so different, but it probably has to do with ridges that form when the skin is first formed, only about 2 months after an egg is fertilized. As the growing layers push and pull, permanent ridges are made. We are born with the same fingerprints that we will have all of our lives.
Though fingerprints are handy for identifying perps, biologically, scientists still aren't quite sure what our fingerprints are for. But as they test different hypotheses, they're getting closer to the answer—and learning some pretty cool stuff in the process.
IS IT TO IMPROVE OUR SENSE OF TOUCH?
In a 2009 study, researchers from the Ecole Normale Superieure in Paris built two biomimetic tactile sensors, which mimic the human ability to touch and perceive texture. One had grooves that mimicked fingerprints; the other was flat like smooth skin. When these faux fingers moved across roughly-textured surfaces, the fingerprinted sensors produced vibrations up to 100 times stronger than the smooth ones. These vibrations, the scientists found, were dominated by a frequency in the optimal range of sensitivity of the Pacinian corpuscles, receptors in our skin that detect pressure changes and vibrations. These researchers think that our fingerprints' job might be to amplify certain tactile information so that it's more easily processed by the nervous system. They also suggest that the swirling patterns of fingerprints ensure that some of the ridges are always brushing sideways across a surface, no matter which way the finger is moving, to better generate vibrations.
IS IT TO IMPROVE OUR GRIP?
Humans, apes, monkeys and koalas all have fingerprints. Some New World monkeys even have ridged pads on their tree-gripping tails. Fingerprints’ design, and their presence in all these animals, has led people to think that they’re an adaptation for improved grip while climbing trees and manipulating objects, but there isn’t much experimental evidence for that. Research by biomechanists at the University of Manchester, who tested the idea in 2009, suggests that a good grip isn’t fingerprints’ forte. Dr. Roland Ennos and his student Peter Warman tested the grip of Warman's fingers at different angles on strips of acrylic glass sheets similar to Plexiglas. While many solid objects obey Amonton's law and friction between them is proportional to the force between them, the friction between finger and glass increased less than Ennos expected when more pressure was applied. The pair inked Warman's fingers to measure the contact area between them and the sheets and found that friction did increase when the contact area increased, but also noted that the grooves between fingerprint ridges reduce the fingers' contact surface with the glass by about one third, compared with smooth skin, and actually reduced friction and ability to grip.
WHAT ARE SOME OTHER POSSIBILITIES?
Ennos and Warman throw out a few other plausible explanations for fingerprints at the end of their paper: that they allow our skin more to more easily comply with and deform to objects we're touching or holding, reducing shear stress and preventing blister formation; that they increase friction on rough surfaces compared with flat skin because the ridges project into the depressions on these surfaces and provide a higher contact area; that they facilitate runoff of water like tire treads. Ennos says his lab is testing all of these hypotheses, but hasn’t published any results yet.
Fingerprints follow us our entire lives. Each little smudge singles us out as distinct individuals among billions of other human beings -- or at least that's what we've always been told.
Even identical twins boast different fingerprints. One crafty Olsen sibling couldn't leave the other's prints on a murder weapon, because all of those unique loops, ridges, whorls and arches were writ inside the womb by pressure on the twins' developing skin.
See, the outer epidermis and the inner subcutaneous tissue sandwich the dermal cell layer between them like a slice of cheese between two slabs of bread. As the pressure builds, this "slice of cheese" compresses and buckles, erupting in random surface patterns [source: Ray].
In fact, the chances of two people possessing an identical fingerprint are slim, though not quite impossible. According to 19th-century polymath Sir Francis Galton, those odds were 1 in 64 billion [source:Stigler]. But according to fingerprinting expert Professor Edward Imwinkelried, since the world population now exceeds 6.4 billion and most of us possess 10 dainty digits, we have more than 64 billion prints out there to bump up the odds of "sharing" a single print with a stranger. That's one reason why multiple fingerprints are important for positive identification; the probability of people having three fingerprints in common are on the order of 100 quadrillion to 1, says Imwinkelried. It's also why he and other experts press for fingerprinting reform and greater reliance on DNA evidence.
According to statistician Stephen M. Stigler, 20th-century reliance on fingerprinting had less to do with science and reliability and more to do with courtroom drama and a fortunate lack of pattern repetition in prints. It's hardly a perfect method. Since 1995, evaluations of fingerprinting labs by Collaborative Testing Services have discovered fingerprinting error rates ranging from 3 percent to 20 percent [source: Arpin].
Fingerprints, the Magic Behind Gripping?
Fingerprints are more than an identification tool and a biological crapshoot. If you've ever considered burning your fingerprints off with acid to avoid arrest (and who hasn't, am I right?), think twice, because fingerprints also help us feel fine textures and minuscule objects.
See, when you feel particularly subtle features -- such as a single human hair on a desktop -- your sense of touch depends on skin vibrations that arise as your fingertips move across the desk.
In 2009, a team of French researchers studied this phenomenon and found that a ridged fingertip moving across a surface produces vibration frequencies that are detected by special nerve endings called Pacinian corpuscles [source: AAAS]. These nerve endings pass this information on to sensory neurons that signal the brain. Burn those prints off and you might dodge a jail sentence, but good luck appreciating -- and feeling -- the finer things in life.
There's another proposal out there, too. Do fingerprints help us grip objects -- say a glass of milk or a battle axe? The idea says that our grooved prints improve the friction rate between our fingers and the object we're holding. But as a team of researchers from the University of Manchester assures us, the whole idea is a bunch of hooey.
In a 2009 study published in the Journal of Experimental Biology, the Manchester team measured the friction rate between flesh and object and discovered only a marginal increase. They also discovered that printed fingerpads actually had 33 percent less contact with an acrylic glass than completely smooth fingerpads. So in some cases, prints actually reduce our grip rather than improve it.
One of the study's leaders, Dr. Roland Ennos, went on to suggest that our prints still may aid us in gripping rough surfaces, or that they may allow our skin to stretch more easily, making it less susceptible to injury [source: BBC].
So that's why you have fingerprints. Now dip them in ink, pudding or delicious Cheetos dust and go share them with the world.
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Author's Note: Why do we have fingerprints?
Fingerprinting is a fascinating area of study, especially when you get past the CSI nonsense and the myth of infallibility. Not every print left by a criminal winds up dusted and, even then, with up to a 20 percent rate of error depending on the lab, who knows whether that print will lead to anyone -- much less the actual perpetrator.
I suppose the take-home is that there's danger in relying on fingerprinting as the sole biometric in identification -- especially when you take into account the 301 post-conviction DNA exonerations in the United States as reported by the Innocence Project as of Nov. 13, 2012.