Fetal Fingerprints

Ever wonder how fingerprints develop or why they are all different?  A couple of commenters on my blog did which got me researching the topic.  After looking through a lot of information on how and when fingerprints develop, I finally found a reputable source.  So without further ado I present to you how and when fingerprints develop.

A working theory of how they formed was developed by two scientist at the University of Arizona named Kucken and Newell.  They basically developed their theory by the use of springs.  

As some of you may know the skin has many layers.  It starts with the epidermis and works down to the dermis and others further down, but for the purposes of fingerprints only the top two layers are important.  The epidermis then has a lower layer (basal layer) and an upper layer.

For the model the scientists assumed that the basal layer of skin was an overdamped elastic sheet trapped between the upper epidermis layer and the lower dermis layer.  What this basically means is that the basal epidermis layer can be thought of as a sheet of plastic that does not oscillate (move up and down) much.     

As the basal layer grows, it is stressed (pushed on) by forces from the upper layer of the epidermis, the dermis, and also by inward pressure from the basal layer itself.  This phenomenon can be modeled by terms of elasticity (how much it can stress), and the solution the scientists found is actually the relatively well known von Karman equations.  Once the stress becomes too much, the basal layer “buckles” and produces the ridges in the epidermis that become your fingerprints.

Using the developed equation it was found that fingerprints develop starting in the nail furrow (top portion of the finger), and in the center of the volar pad (center of finger). These then stretch out until the entire finger is covered in fingerprints.  

The main reason everyone’s fingerprints are unique is that everyone had different stresses applied to their basal layer during fetal growth.  Everything from the orientation the fetus is in to the amount of movement the fetus experiences helps differentiate fingerprints.  Even identical twins grow in different orientations and experience different stresses, thus they have different fingerprints.  

Finally, when do the fingerprints develop? Surprisingly early in the fetal development process; fingerprints begin to develop at around the 10^th week of pregnancy and they are set in stone by the 17^th week of pregnancy.  That means that about four months into pregnancy the baby already has defined fingerprints that will be the same throughout their lifetime.  

I find this information to be fascinating and more proof of how amazing the human body is.  Did you know that fingerprints developed so early in the stages of pregnancy? That was shocking to me since I thought fingerprints would be one of the last things to develop.  Let me know if you have any questions and I will try to answer them as well as I can!   

Source:

M. Kucken, A. Newell. A model for fingerprint formation. Europhysics Letters. October 2004. Link