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.
Your tongue is attached pretty well to the floor of your mouth. Learn whether it is really possible to swallow your tongue at HowStuffWorks.
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.
- American Association for the Advancement of Science (AAAS). "Why fingerprints?" Jan. 30, 2009. (Nov. 6, 2012) http://chinese.eurekalert.org/en/pub_releases/2009-01/aaft-wf012609.php
- Arpin, Tina. "Faulty Fingerprints." Triplepoint. 2005. (Nov. 5, 2012) http://www.bu.edu/sjmag/scimag2005/opinion/fingerprints.htm
- Cherry, Michael and Edward Imwinkelried. "How can we improve the reliability of fingerprint identification?" 2006. (Nov. 5, 2012) http://www.ajs.org/ajs/publications/Judicature_PDFs/902/Cherry_902.pdf
- "Fingerprint grip theory rejected." BBC News. June 12, 2009. (Nov. 13, 2012) http://news.bbc.co.uk/2/hi/health/8093134.stm
- Ray, C. Claiborne. "Q&A: Twins and Fingerprints." The New York Times. Oct. 5, 2009.(Nov. 6, 2012) http://www.nytimes.com/2009/10/06/science/06qna.html?_r=0
- Stigler, Stephen M. "Galton and Identification by Fingerprints." Genetics Society of America. 1995. (Nov. 6, 2012) http://www.genetics.org/content/140/3/857.full.pdf