Why Even Identical Twins Have Different Fingerprints

Fingerprints on a white background — Fingerprints are primarily made up of arches, loops and whorls and sometimes a combination of all three. MirageC/Getty Images

One of life's great marvels is that, much like snowflakes, no two fingerprints are alike. This goes even for identical twins, who split from the very same egg. In fact, fingerprints are so unique that we actually have different prints on each and every digit! Although it's not entirely impossible for two fingerprints to match up, the odds are way against it, at 1 in 64 billion. Definitely not odds you want to take to Vegas, right?

Fingerprints have been studied for millennia, but the Federal Bureau of Investigation (FBI) today identifies eight primary types of fingerprint patterns. These include four types of loops, two types of arches, one type of whorl and even an accidental type, which combines characteristics of all three patterns. But even within those patterns, there's tremendous potential for differences in spacing, depth, angles and such. A print's pattern depends on a potent and unique combination of genes plus environment during development.

How the Womb Environment Affects Fingerprints

Human skin is easily affected by its environment. That's why people who spend a lot of time in the sun or doing manual labor tend to have freckled, sunburned or tougher skin than those who hang out in the shade. This tendency begins in the womb. In fact, as a fetus grows, the epidermis and the dermis (the outside and inside layers of skin) come together naturally, which produces friction ridges. The ridges get their basic design from the genes of the baby's parents, but fetal cells work at their own individual pace, which causes the skin to grow and stretch and move in different ways.

A fetus' budding fingertips, which develop between 13 and 19 weeks of gestation, can also be influenced by the nutrients it is getting, how it's positioned in utero or even if it rubs against the womb or umbilical cord. Once a fingerprint is developed, it remains static for the life of the person in question, barring major skin diseases, burns or scarring, of course.

How Genetics Affects Fingerprints

A fingerprint scanner is integrated into a printed circuit. A fingerprint's unique characteristics are based on a person's genes plus environmental factors they experienced in the womb. Surasak Suwanmake/Getty Images

Even the most identical of twins can experience individual genetic mutations, making them ever so slightly different from each other. In fact, signaling pathways help the genes communicate to complete their individual instructions. These are very sensitive to the womb's environment, which is why identical twins are not 100 percent genetically alike, as previously thought.

According to a recent study, three different chains of signaling in particular appear to affect how the fingerprint develops. Very active BMP (bone morphogenetic protein) pathways have been found to tamp down the growth of ridges, whereas Wnt (Wingless-related integration site) pathways encourage them to develop. However, EDAR (ectodysplasin A receptors) affect how big or small the ridges or whorls are, and also how they're spaced out. Since everyone's pathways and signals are different, these affect how the fingerprints turn out. In short, a zillion little factors come into play when the skin layers first form to create something that's truly one of a kind.