For quite a while now, fingerprints have been used as an identification tool, both at crime scenes and for general use. It is the three special characteristics of fingerprints that allowed it for its use. The first being its individuality, the second being its durability, by which I mean its ability to remain unchanged throughout a person's life, and the third being the fact that fingerprints can be systemically and neatly classified into different groups.
No two individuals have the same fingerprint
It is generally believed that we would not find anyone in the world with the same fingerprint. Francis Galton, who published the text book "Finger Prints" in 1892, claimed that there could be 64 billion different fingerprints. Although the validity of his calculations has been questioned, it is nonetheless agreed among experts that the chance of two people having the same print is extremely rare. Studies on the fingerprints of millions of people in the past 110 years have proved that this is the case. The FBI alone has about 50 million fingerprints in their database, none of which are the same.
To determine whether two fingerprints match, one must carefully study the prints' ridge characteristics (minutiae) and if two prints are the same, they must have the same characteristics at the exact same location. Several points are often compared. It is said that an average fingerprint would have about 150 individual ridge characteristics. At crime scenes however, prints can often be partial. This is not a problem though as usually only eight to 16 ridge features are needed to determine if two prints are identical.
Fingerprints remained unchanged throughout life
Fingerprints are basically reproductions of friction skin ridges; and similar systems can be found on the palm and the soles of one's feet, done so in order to allow a better grip on things. By looking closely, you will find that your prints are actually a series of lines made up of hills (ridges) and valleys (grooves).
On the outermost layer of your finger, there is the epidermis, and below that there is the inner dermis. In between the two layers is a boundary layer made up of dermal papillae. It is the shape and pattern of this layer that determines the pattern of ridges as appears on the skin. Therefore, our fingerprints have actually been formed ever since we were a fetus and it simply enlarges and stretches out as we grow up. The ridges are actually openings to ducts leading to sweat glands. It is therefore a mix of perspiration and body oils that leave fingerprints on objects.
There have been cases in history when people tried to remove and change their fingerprints but the outcome was always fruitless. Fingerprints always grow again; and adding scars to one's fingers usually only makes them even more recognizable.
Classification of fingerprints
There are three major classes of fingerprints, classified based on their general loop patterns. Fingerprints can either be loops, whorls or arches. About 60-65% of people in the world have their fingerprints appearing as loops, about 30 -35% have whorls and only about 5% have arches.
Loops are fingerprints that have their ridges entering from one side of the finger, recurving and exiting through the same side. If the opening is towards the little finger, it is called an ulnar loop. If it opens towards the thumb instead, it is called a radial loop.
Whorls are fingerprints that include ridge patterns that are usually round or circular in shape and have two deltas. They can be sub-classified into four groups, namely plain whorls, central pocket loop whorls, double loop whorls and accidental whorls.
Arches, the third and last group, are prints that have ridge lines entering and leaving on different sides. They can be either tented arches or plain arches. This is the simplest group of fingerprints as arches don't have characteristics such as type lines, deltas or cores.