Scientific Principles of Fingerprints Flashcards
What is a fingerprint?
The term fingerprint is a generic term used to refer to impressions formed by the skin on the undersides of the fingers, as well as the palms and soles of the feet.
This skin is different to the skin elsewhere on the body, as it is covered in rows and patterns of small ridges called friction ridges.
When we touch a surface, the sweat that lines these ridges is transferred to that surface, forming an impression that replicates the unique features of the friction ridge skin. This impression is called a fingerprint.
We also refer to some fingerprints as ‘latent fingerprints’, and these are fingerprints that have been located and preserved from a crime scene.
What key principles do fingerprint identifications rely on?
Fingerprint identification relies on two key principle which relate to the way in which the arrangements of friction ridges on the undersides of the hands and feet are both unique and permanent.
The friction ridges form while we are still developing inside of the womb, and rather than forming continuous, uniform rows of ridges, these ridges form a range of different features (such as those mentioned in my annexure).
The exact shape, location, and sequence of these features is determined by a combination of the individuals genetics and a multitude of factors which relate to the womb environment - such as the mother nutrition, the position of the foetus inside of the womb – all of which affect the timing and rate of ridge development.
No two people share the same fingerprints because not two people are exposed to the same combination of these factors while they are developing inside of the womb.
The friction ridges also remain permanently in the same arrangement for our entire lives and can only change due to deep tissue injury which disrupts the formation of ridges and results in the formation of scarring on the skin surface. However, these scars act as additional unique features that can contribute to a fingerprint identification.
What is a fingerprint made of?
Fingerprints are most commonly composed of a combination of sweat, and any other material on the skin (such as sebum, dirt, or grease).
The composition of fingerprints largely depends on what we have been touching recently with our hands. For example, if we have been touching our hair or face recently, there will be sebum on our hands, and so our fingerprints will also contain sebum.
Can you explain what factors determine whether a fingerprint is left on a surface?
Several factors determine whether a fingerprint is left on a surface when we touch it, including:
The condition of the person’s skin - the prominence of the friction ridges can be affected by some skin conditions, as well as age.
The amount of sweat (and other residue) on the skin at the time - fingerprints can only be left if there is some residue to be transferred.
The texture and cleanliness of the surface being touched - fingerprints are more likely to be left on clean, smooth surfaces (such as a glass cup), as opposed to dirty or textured surface.
How do you know that fingerprints are unique and permanent?
The uniqueness and permanence of friction ridge skin has been the subject of scientific research for more than a century, which has consistently supported these two principles.
This research began with the likes of William Herschel who first described the uniqueness and permanence of friction ridge skin in the late 19th century, and more recently, twin studies have looked deeper into the mechanisms of uniqueness.
In my own experience, I have compared thousands of fingerprints whilst working in my role and have never found the fingerprints from two different people to be the same. I have also compared the fingerprints of the same person, recorded years and even decades apart and have found no differences to the configuration of their fingerprints.
What are the unique features of a fingerprint?
The rows of friction ridges that cover the undersides of the hands and feet are not constant and uniform, but instead these ridges stop and start forming what we call ridge endings, and split into two to form what we call bifurcations. These features occur in random locations throughout the friction ridge skin.
We examine the location and sequence of these ridge features, along with supplementary features such as scars and creases, when analysing and comparing fingerprints.
What chance is there that two people share the same fingerprints?
While it is possible to find two people who share very similar fingerprints, no two people share the exact same fingerprints due to the unique combination of genetic and environmental factors which influence the formation of friction ridge skin during foetal development.
Even identical twins, who present the greatest possibility of sharing the same fingerprints due to sharing almost identical genetics and the same womb during development, have different fingerprints due to slight differences in the way in which they interact with their womb environment during development.
Is fingerprint identification a science?
Yes, fingerprint identification is a science, as it is built on the scientific principles of biological uniqueness and permanence.
Also, the fingerprint identification methodology is based on the scientific method, which involves forming conclusions based on observations, which are then subject to peer review.
Has fingerprint science been peer-reviewed?
All scientific research that is published in the field of fingerprint science is subject to peer review prior to publication.
How long do fingerprints remain on a surface?
Fingerprints are often fragile and can be easily rubbed or washed off a surface, so the length of time that a fingerprint remains on a surface depends on how well-protected it is from the environment and people touching the surface.
For example, a fingerprint on a bottle that is kept in a cupboard for a long period of time will last longer than a fingerprint on a bottle that is left outside, where it is exposed to the sun and rain.
For this reason, I would not expect a fingerprint left on the outside of a vehicle to last a long period of time (i.e. no more than one or two weeks), particularly if that vehicle has spent a lot of time outside where it is exposed to the elements.
