Curiosity 4 of 10
4. Identical twins don't have the same fingerprints
Even with nearly identical DNA, identical twins have different fingerprints. The fine pattern of the fingers also depends on what happens to each baby inside the womb.
A pattern made before birth
The ridges of the skin on the fingers begin to form around the 10th week of pregnancy and become defined in the middle of the pregnancy. After that, the pattern no longer changes: it only grows along with the hand.
Genes influence the general type of the pattern, such as loops, arches and spirals, which is why twins tend to have similar patterns. But the details, such as the points where a line ends or splits, depend on factors like the baby's position, the pressure of the surrounding fluid and the growth of each finger.
Because each twin occupies a different place in the womb and moves in its own way, these details turn out differently. These are exactly what experts compare to identify a person, and that is how the fingerprints of identical twins can be told apart.
A fingerprint can become hard to read over time, through wear from manual work or with age, but the basic pattern stays the same. Small cuts heal without changing the pattern; only deeper scars leave new marks.
Did you know? Koalas also have fingerprints, and they are so similar to human ones that, even under a microscope, it is hard to tell them apart.
