By the 17th week of pregnancy,
the fingerprints of a fetus are set. The uniqueness of fingerprints
has been recognized and studied scientifically for two centuries,
but researchers have not been able to explain exactly how they form.
A new theoretical computer model describes how the patterns are
likely created, beginning in the 10th week of gestation, when a
fetus is about 3 inches (80 mm) long.
Researchers at the University of Arizona found that creation of the
patterns involves stresses in a sandwiched sheet of skin called the
basal layer. In a fetus, the basal layer grows faster than
surrounding layers, the outer epidermis and the inner dermis. The
basal layer buckles and folds in several directions, forcing complex
shapes. Stresses are created at skin boundaries, including
fingernails and knuckle creases, as well as around shrinking
fingertip pads.
The fingerprint pattern is coded underneath the skin surface, does
not change as we age, and the pattern cannot be destroyed by
superficial skin injuries.
General characteristics of fingerprints can be inherited, so family
members do tend have similar, but still unique fingerprint patterns.
Even Siamese twins and identical twins have varying fingerprints.
Fingerprints are impressions made by the ridges on the ends of the
fingers and thumbs. These ridges provide friction, or traction, when
we grasp objects so that those objects do not slip through our
fingers. Fingerprints are on the fingers and palms, but not on any
other places of the skin. Scientists also believe that they may
enhance our sense of touch.
Koalas have ridges on their fingers which create fingerprints very
much like those of human beings.