Fingerprint Patterns Before Birth

Our fingers and toes have some patterns on them.

These impressions are known as ‘fingerprints’.

Fingerprints are the grooved impressions from the ridges present on our fingers and toes. This corrugation arises from the folding of the upper layer of fingertip skin, called the epidermis.

Such elevated epidermal layer is known as ridges and the grooves formed due to them are known as valleys or furrows.

These friction ridges thus upon contact with any surface produce impressions that persist whole life. This persistence of fingerprint impression resists in its morphology and physiology, but its uniqueness lies in the embryology of fingerprint. 

Fingerprint Development in The Womb

Frictional ridges are estimated to be established around 10.5 and 16 weeks EGA (Estimated Gestational Age) during gestation due to developmental noise also known as Buckling instability.

During embryonic development, the embryo undergoes several cell divisions and cleavages that lead to the differentiation of cells. This movement of cells is known as the process of ‘Gastrulation’, involves the development of primary tissue distinctions between ectoderm, mesoderm, and endoderm. The ectoderm will further develop into Epidermis, which possesses Friction ridges. 

Volar Pad Regression

During late embryological development, ‘morphogenesis’ or the formation of shape takes place.

Limbs start rapidly developing from about 4 weeks EGA.

By the end of the second month, the arms, legs, knees, elbows, fingers, and toes can all be seen.

Also, the hand changes from a paddle-like form to an adult form, including the formation of the fingers and rotation of the thumb.

Swelling of mesenchyme called “volar pads” appears on the palms of the hands and soles of the feet at this time.

Frictional ridges start developing due to this buckling instability in the basal cells (volar pads) of the fetal epidermis.

The volar pads start developing on the fingertips around 7–8 weeks EGA, which starts from the thumb to the little finger in the same radio-ulnar gradient that ridge formation, will follow.

Buckling direction is always perpendicular to the greatest stress in basal cells, which is induced by the resistance between furrows and creases.

This friction leads to the differential growth of the basal layer and regression of the volar pads during the time of ridge formation.

After 10 weeks EGA, volar pads start regressing both in shape and position. ‘Regression’ is the process of the slow growth of volar pad on the rapidly growing surface that causes its contour to be less distinct.

During the second trimester, the placenta secretes several hormones vital for bone growth and energy.

As development proceeds, a volar pad regresses, and frictional ridge development proceeds.  Frictional ridges continue to grow until about 16 weeks EGA when ridge characteristics or minutiae become set.

Primary Ridge Formation

At around 10–10.5 weeks EGA, basal cells of the epidermis begin to divide rapidly.

Friction ridges are also known as ‘Papillary ridges’. As the name suggests, epidermal ridges extend and are embedded into the dermis.

Primary ridges are the first visual evidence of interaction between the dermis and epidermis and are continuous ridges.

 Activation of the center of proliferation that will become the site for sweat gland development later begins around 10.5 weeks EGA.

These ‘site’ or ‘units’ develop along with the line of relief perpendicular to the direction of compression.

After some time the proliferations get merged, which results in the folding of linear ridges into rapidly dividing epidermal cells. Thus, this fusion creates the first visible ridge structure at the epidermal-dermal junction. 

There have been various researches in order to link the role of the nervous system in proliferation and primary ridge alignment.

Later discoveries confirmed the neurological relation of spinal cord sections C–6, C–7, and C–8 to innervations of the fingers.

The fact that nerves are present within the dermis earlier than ridge formation suggests its role in proliferation and ridge formation.

Minutiae Formation

From the perception until maturation, i.e., 10.5 to 16 weeks EGA, primary ridge maturation continues.

The formation of new ridges continues while the separation of existing ridges starts because of the growth of digits.

This separation of existing ridges results in the formation of Friction characteristics/ Minutiae.

According to various theories, minutiae formation can be either mechanical (static) or chemical (fusion). However, it is governed by infinite interdependent forces acting upon that area. 

Secondary Ridge Formation

By the end of the second trimester, sweat glands mature and the epidermal-dermal ridge system continues to grow in size and mature.

Sweat ducts and pores start to develop as well.

At the end of the 15 week EGA, ridge growth appears to be in two directions: downward penetration of the sweat glands and upward growth of new cells.

Generally, the entire volar surface is ridged by 15 weeks of EGA. Secondary ridges are cell proliferation resulting in down folds of the basal epidermis. By this time all the randomly located minutiae patterns become permanent within the friction ridge pattern.

Pattern Formation

The fetal volar pads influence ridge pattern formation (volar pad symmetry) and ridge count (volar pad size). 

But the volar pads do not directly cause ridge alignment.

Instead, the palmar pads have an effect on the topology of the surface and also the overall tension and compression across the developing epidermal-dermal junction, which successively directly affects friction ridge alignment throughout the essential stage of ridge development.

Any stress or strain on the developing finger throughout the essential stage of friction ridge formation may have an effect on ridge alignment.

Fingerprints on Other Surface

As discussed earlier, the fingertip skin layer contains thousands of sweat glands that open via ducts onto small funnel-shaped openings or ‘pores’ present on the ridges.

The discharge excreted by the sweat gland then gets deposited on the surface upon contact.

The sweat glands' secretion is consist of 99% of water.

In addition, various inorganic salts, as well as organic matter such as urea and fatty components are present in the discharge.

Also, our hand are free moving and often tends to touch the face and hairs which results in the deposition of oily secretion from the sebaceous glands present on the hair-producing area of the skin.

And when the finger comes in contact with any surface some of the excretions from sweat and sebaceous gland get transferred, though invisible to naked eyes. 

Importance of Fingerprints 

Identification of a person is the sole purpose of a criminal investigation.

Earlier police have always sought an infallible human identification system.

The very first such systematic system was developed by French Police Expert Alphonse Bertillon in 1883.

It was based on developing detailed body measurement profiles.

In the early years of the twentieth century, it was only when the Bertillon system couldn’t recognize twins Police began to accept the Fingerprint identification system.

Now, fingerprint identification has become a very important part of forensic and criminal investigation.

Fingerprint plays a vital role as Forensic evidence due to its following characteristics:-   

Uniqueness: No two fingers have the same pattern, not even for the same person. However, this uniqueness or individuality is not just based on the general pattern of fingerprints but a very detailed study of its ridge characteristics. In court, a point-by-point comparison must be explained by the expert during trial for the establishment of the identity of the individual.

Universal: Each and every individual have fingerprints all over the world. Hence, chances of getting a fingerprint at the crime scene are very high.

Permanent: Fingerprints do not alter throughout life. They remain persistent throughout their life. Only when a person dies, upon decomposition, it disappears.

Speedy investigation:  Locating and developing fingerprints is easy and rapid as well.

Easy classification: Fingerprints have a general pattern that can be easily classified systematically.

Reliable piece of evidence: Since fingerprints are inimitable, they serve as a reliable piece of evidence. 

Reference

1. Kücken M, Newell AC. Fingerprint formation. J Theor Biol. 2005 Jul 7;235(1):71-83. doi: 10.1016/j.jtbi.2004.12.020. PMID: 15833314.

https://pubmed.ncbi.nlm.nih.gov/15833314/

2. THE FINGERPRINT SOURCEBOOK, US Dept. of Justice – Ch3: Embryology & morphology of friction skin ridge, Kasey Wertheim; [Page no. 3-4 to 3-12]. https://www.ojp.gov/pdffiles1/nij/225320.pdf

3. Fingerprints in Criminal investigation, M. Edwin O'Neill, Fingerprints in Criminal Investigation, 30 Am. Inst. Crim. L. & Criminology 929 (1939-1940).

4. https://www.legalserviceindia.com/legal/article-2463-fingerprints-a-forensic-tool-for-criminal-investigation.html

5. Forensic Science, Richard Saferstein, 2nd Edition, Page no. 163-167.

6. epg-Pathshala, PAPER No. 3: FINGERPRINTS AND OTHER IMPRESSIONS, MODULE No. 2: The Basis of Fingerprints Identification.