Fingerprints have been used as a means of identification for over 100 years as they are permanent and unique structures.
When are fingerprints formed?
Between the 10th and 24th week of gestation in the womb, the skin on the underside of the foetus’ hands, fingers, feet and toes develops and goes through rapid growth. The growth causes a huge amount of pressure and strains on the skin, causing it to buckle into folds. These folds reach all the way to the inner layer of the skin, i.e. the dermis, where it becomes anchored in place. The skin forms a complex friction ridge pattern and is the foundation of our permanent fingerprint.
What role does genetics play in determining fingerprints in identical twins and more?
The friction ridge pattern is determined by both genetic and unique physical conditions.
Genetics generally decide the timing and the position of the skin as it grows and buckles, which is why you end up with potentially similar looking fingerprints to your siblings and your parents. The similarities primarily occur on what they call 1st level friction ridge detail; the overall flow of the ridges.
You can have loops, arches and whorls as overall ridge flow. A loop shows the ridges entering on one side of the finger, looping around and then exiting on the same side of the finger. An arch has a ridge flow that enters on one side of the finger, goes up, and then down as it exits the other side of the finger, like a wave. A whorl formation looks like a circle or sometimes an ‘S’ shape.
What role do environmental factors play in determining fingerprints in identical twins and more?
When you start looking a lot closer at the fingerprint, you start noticing 2nd level detail such as a ridge ending or a bifurcation (where the ridge splits). These little details are called minutiae and when you compare your fingers to someone else’s, you will find that the patterns formed by these minutiae are different, no matter how similar the 1st level detail looks.
This is because innumerable environmental factors are thought to influence the formation of fingerprints, such as blood pressure, hormone levels, the exact position of the foetus in the womb and the complexity and density of amniotic fluid. A huge number of variables decide how each ridge is formed. The complexity of the conditions within the womb prevents fingerprints from developing exactly the same way in any two foetuses.
Study: A Computational Discriminability Analysis on Twin Fingerprints
Sharing similar genetic traits makes the investigation of twins an important study in forensics and biometrics.
In 2009, a study was done where fingerprints from both fraternal and identical twins were compared to test whether fingerprints from twins were more similar to each other than to those of the public.
298 pairs of twins were studied, and the results showed that 1st level detail between twins were highly correlated in ridge flow and pattern (62.78% for both fraternal and identical) compared to the public (32%).
Minutiae characteristics (2nd level detail) were similar between twins, however there was still a significant discriminable difference between twins and non-related persons despite having similar pattern types and ridge flow.
Images of fingerprints in identical twins and more
The images of (a) and (b) are the index fingers of identical twins, while image (c) is the index finger of an unrelated person. You can see that the twins have very similar looking fingerprints and have more points of similarity between each other than compared to that of an unrelated person with similar fingerprints.