The idea of using a fingerprint as a means of identification is ancient. Literally.
“There is archaeological evidence that fingerprints as a form of identification have been used at least since 7000 to 6000 BC by the ancient Assyrians and Chinese. Clay pottery from these times sometimes contain fingerprint impressions placed to mark the potter. Chinese documents bore a clay seal marked by the thumbprint of the originator. Bricks used in houses in the ancient city of Jericho were sometimes imprinted by pairs of thumbprints of the bricklayer. […]
In the mid-1800’s scientific studies were begun that would established two critical characteristics of fingerprints that are true still to this day: no two fingerprints from different fingers have been found to have the same ridge pattern, and fingerprint ridge patterns are unchanging throughout life. These studies led to the use of fingerprints for criminal identification, first in Argentina in 1896, then at Scotland Yard in 1901, and to other countries in the early 1900’s.
Computer processing of fingerprints began in the early 1960s with the introduction of computer hardware that could reasonably process these images. Since then, automated fingerprint identification systems (AFIS) have been deployed widely among law enforcement agencies throughout the world.” 
You get the idea. Because fingerprints have been used for identification for so long, the definition of the term has expanded to include “any unique or distinctive pattern that presents unambiguous evidence of a specific person, substance, disease, etc.” 
They’ve been used for millennia and studied for centuries, yet there are still things to be learned about the kind of fingerprints that are at the tips of your fingers. And so, I will first look at some research related to the human biology of fingerprints.
A finger pad fingerprint: what is its purpose?
Identification is a “use” of fingerprints, but not necessarily a “purpose”. Is there a biological purpose for fingerprints? It has long been supposed that the ridges on the tips of our fingers help us to grip things by increasing the friction between the finger and the object.
There are two aspects of that statement worthy of exploration: that fingerprints help grip and that they do so by increasing the friction between the objects. Dr. Roland Ennos and his student Peter H. Warman of the University of Manchester, UK, looked at the latter: do fingerprints increase friction?.
The amount of friction between two objects is related to the surface area in contact and to the amount of pressure between the objects. For hard objects, friction increases with increased pressure between them. For rubbery objects, friction increases with the amount of area in contact.
For their experiments, Ennos and Warman designed equipment that would move a piece of acrylic glass along the finger pad. Pressure was varied as was the width of the piece of glass. Counter to expectation, fingertip friction was higher when more fingertip area was in contact with the glass, more similar to the way a rubbery object would behave. The ridges themselves reduced the contact area as compared with flat skin. So, if the fingerprint ridges do help us grip things, the researchers concluded that it is unlikely to be because of increased friction.
A fingerless fingerprint: the community of bacteria on your hand
I guess it comes as no real surprise that along with your fingerprint, the tip of your finger also contains a community of bacteria. What may be a bit surprising is that the bacterial composition of that community remains fairly constant over time and that it is highly individualized.
Dr. Noah Fierer (Colorado University at Boulder, USA) and his colleagues conducted a series of studies of hand bacteria left behind on surfaces (like computer keyboards and mice). They showed that you can collect skin-associated bacteria from these surfaces, that the bacteria are there for up to two weeks after the objects have been touched, and that the bacterial community is fairly unique to individuals.
Areas of further research include validating the method and retrieving and testing the longevity of bacteria on different surfaces, e.g., fabric, plastic, and metal.
Another important issue brought up by this kind of research is that of bioethics. Since this is a new technique, there are currently no laws governing its use, so there is a privacy concern regarding the identification of individuals via their hand bacteria. .
A body-less fingerprint: the chemical composition of an oil spill
The recent oil spill in the Gulf of Mexico has led to a series of news stories on oil spills, clean-up techniques, and the like. The report that relates to the theme of this article was about chemical fingerprinting of oil spills.
“Chemical fingerprinting is matching certain chemical characteristics in oil to a known standard or to a suspected standard. Just for example, it’s almost like matching scratches in a gun barrel when forensic people look at bullets and where they come from. So, some of the same sort of techniques used to be used and now they’re becoming much more chemical and perhaps much more mathematical,” explains Dr. Merv Fingas, former Chief of the Emergencies Science Division of Environment Canada and leading expert in oil spill research.
He went on to explain that all oil spills are quite unique and that oil from particular wells is unique. Even though they change somewhat over time, the “chemical signature will be much more unique than even a neighboring well and definitely much more unique than crude oil from a distant well.”
The field of oil fingerprinting began 40 or more years ago as an outgrowth of studies of oil chemistry for refinery purposes, when it was discovered that the gas chromatography of different wells had different patterns. These patterns could then be used to distinguish pipeline contents, for example. Modern uses of the oil fingerprint include determining the source and nature of spills, and predicting and measuring environmental damage.
Source determination is useful, for example, if there is a spill along a particular shipping lane. Samples are taken from that spill and compared to the contents of vessels that had passed through that lane. A match is nearly always found.
The fingerprint can also be used to follow the pattern of the spill, its nature. With the recent gulf spill, tar balls will come ashore a few weeks before the main spill comes. Matching the tar back to its originating spill can help determine which way the spill is travelling.
Knowing the source of oil that washes up on shore enables scientists to measure long-term environmental damage from a spill. The most commonly cited case is the 1979 Ixtoc blowout in the Gulf of Mexico near the Yucatan Peninsula. It has been reported that tar balls from this spill are still coming up on beaches in Texas. If that is indeed the case, then it is easy to see how oil spill fingerprinting could help predict the behavior and environmental impact of more recent spills.
Pattern Recognition in the Media:
Fingered and Fingerless Fingerprints
by Linda J. O’Gorman (USA)
For more information:
A fingerpad fingerprint
“Fingerprints are unlikely to increase the friction of primate fingerpads,” by Peter H. Warman and A. Roland Ennos, Journal of Experimental Biology 2009 212.
A fingerless fingerprint
“Forensic identification using skin bacterial communities,” by Noah Fierer, Christian Lauber, Nick Zhou, Daniel McDonald, Elizabeth Costello, and Rob Knight, Proceedings of the National Academy of Sciences
“New CU-Boulder Hand Bacteria Study Holds Promise for Forensics Identification,” by Noah Fierer, Rob Knight, Jim Scott, University of Colorado at Boulder News Center, March 15, 2010.
A fingerpad fingerprint
“Getting a grip on fingerprints,” The Week Magazine, July 3-10, 2009.
A fingerless fingerprint
“Given away by your bacteria,” The Week Magazine, April 2, 2010.
A body-less fingerprint
“Underreported: Chemical Fingerprinting of Oil Spills”, The Leonard Lopate Show, WNYC, New York, June 24, 2010
 L. O’Gorman, “Fingerprint Verification,” in Biometrics: Personal Identification in Networked Society, edited by Anil Jain, Ruud Bolle, Sharath Pankanti, Kluwer Press, The Netherlands, Nov. 1998, pp. 43-64.
 Dictionary.com based on the Random House Dictionary.