(FPT) Introduction to Fingerprints Lesson

Introduction to Fingerprints

Dactylography, or the scientific study of fingerprints as a means of identification, is a very important part of Forensic Science. Fingerprints are one of the most reliable sources of individual evidence and they are a staple in most criminal cases when they are found in a crime scene. Fingerprints are a reproduction of friction skin ridges found on the palm side of fingers and thumbs. Friction skin ridges are also found on soles of feet and toes and can also be used to identify a person. Fingerprints are left behind due to sweat, oils, and dirt found on our hands. Fingerprints have been used for centuries to identify people and can be found on nearly every surface. This abundance of evidence littering the surface of so many objects is great news for investigators because fingerprints are considered individual evidence and may provide the key to solving a case.

To understand how a fingerprint is left on a surface, one must first understand the structure of the skin. A person's skin is composed of 3 layers; the epidermis, dermis and hypodermis. The epidermal surface is composed of ridge and groove features. Each ridge is dotted with sweat pores along the entire length. The Eccrine sweat glands are responsible for the production of the residue that makes up a fingerprint left on a surface. These sweat glands are located mainly in the palms of the hands and soles of the feet. They secrete a liquid that is 99% water and 1% chlorides, metal ions and amino acids. Another type of sweat gland, known as the Apocrine Sweat Gland, is found in the hair follicles. Apocrine glands secrete cytoplasm and nuclear materials, including inorganic compounds, such as ionic iron, and organic compounds such as proteins, carbohydrates and cholesterol. Sebaceous glands are found in places where hair grows. These glands secrete an oily substance known as sebum. Sebum includes organic compounds such as fatty acids and glycerides, as well as alcohols and hydrocarbons. Fingerprints can be composed of any of the fluids from the Eccrine, Apocrine or Sebaceous glands. Here is an image of the layers of the skin:

The epidermal layer is anchored to the dermis by the dermal papillae. In human skin, the dermal papillae are small hills of dermis that project into into the epidermis. At the surface of the skin in hands and feet, they appear as epidermal or papillary ridges. These papillary ridges are more commonly known as fingerprints! The dermal papillae layer grows very fast which causes it to collapse resulting in the formation of unique patterns within the fingerprint. Since the dermal papillae are formed during fetal development, the pattern generated from this "collapse" will remain the same throughout a person's life. The individual skin ridges form in fetal development in the womb due to the pressure of the amniotic fluid against the fingertip pads of the fetus. The hypodermis is the innermost layer of the skin containing fat deposits that give the body its contours and energy reserves.

Fingerprints are even more unique than DNA! No two people have ever been found to have the same fingerprints, whereas DNA can be shared between identical twins! Identical twins are produced from the same egg and sperm and therefore have identical DNA; fingerprints form separately on each twin as a result of amniotic fluid pressure on the developing skin. Additionally, fingerprints are often the way in which identical twins are differentiated in criminal cases. In July 2008, a woman was murdered in Georgia after a carjacking. The police found a cigarette at the crime scene with DNA matching a man identified as Donald Smith. When interrogated, Donald Smith denied that he had anything to do with the murder. When police showed him a video of the carjacking, Donald said that it was actually his identical twin brother Ronald. Authorities questioned his family and they also confirmed that the man in the video was Ronald. Police found a fingerprint in the car and were able to link it to Ronald. When confronted with DNA, video surveillance and a matching fingerprint, Ronald confessed to the crime. If a fingerprint had not been found, Donald could have been mistakenly convicted for a crime he did not commit!

Interactivity: History of Fingerprinting

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