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Fingerprints persist, Chameleons can see red (unscathed)
Q: When skin on fingertips grows back from injury or an
accident does the fingerprint have the same pattern as before or a new pattern?
(Cynthia, Goldsboro, North Carolina)
A:
New skin usually keeps the old pattern. That swirling, looping pattern of ridges
and furrows on fingertip skin that forms a fingerprint usually stays with a
person for life — from formation in the mother’s womb to death. Gangster John
Dillinger, who in 1930 drenched his fingertips in acid to remove the ridge
patterns, failed miserably. His old pattern reappeared as the tips healed.
 Fingerprint, showing a whorl pattern. [Federal Bureau of
Investigation]
Fingerprint patterns can change, though. To understand how,
let’s look at the structure of the skin.
The skin — our largest organ — is divided into two parts:
a thin almost transparent outer skin, called the epidermis.
It walls us from the outside world like a protective shield and houses the
ridges and furrows that make fingerprints.
an inner soft-tissue skin (the dermis), which is filled
with nerves, glands, and pipes carrying blood and lymph. The dermis also
contains a double row of "pegs," called the dermal papillae http://www.meddean.luc.edu/lumen/MedEd/medicine/dermatology/melton/skinlsn/papderm.htm.
These "pegs" anchor the outer skin (with its fingerprints) to the inner skin
and they create fingerprints.
The double row of "pegs" in the inner skin pokes up and makes
fingerprint ridges in the outer skin.
We
can envision how the "pegs" make fingerprint ridges that resist change with the
help of some clothespins and pink plastic wrap. Imagine setting out a double row
of clothespins as the fingerprint "pegs." Lay a piece of plastic wrap (outer
skin) over the double row, poking it down between the clothespin rows. The
plastic wrap hits the clothespin tops and forms two parallel ridges — with a
furrow in between — much as the skin "pegs" create fingerprint ridges and
furrows. See figure.
 Clothespin rows draped in plastic wrap to illustrate the
dermal structure underlying fingerprints. [April Holladay, WonderQuest]
When the fingertip outer skin gets injured, new cells replace
the old. Like laying a new piece of plastic wrap over the clothespin rows, the
ridges and furrows remain unchanged because the skin "peg" rows are unchanged.
Scarred skin is denser, thicker, and whiter but the ridge patterns look the
same.
Damage the "pegs" (dermal papillae) in the inner skin,
however, and you can change the double-row layout and, hence, the ridge pattern.
Then and only then, the skin grows back with a new fingerprint pattern.
That’s what another gangster, Robert Phillips, tried when he
had a plastic surgeon remove the skin — outer and inner — from his fingertips
and replace it with skin grafts from his chest. To no avail! The FBI simply used
prints from his undamaged second joints to identify him.
Further Reading:
Loyola University Medical Education Network: Dermatology Atlas by Jason R.
Swanson and Jeffrey L. Melton
FBI:
Taking legible fingerprints
Q: When I was a child I
lived in southern Africa. We used to get quite a few chameleons. I was told that
putting them on a red background caused them stress that could eventually lead
to their death. I was only about 5 or 6 years old but the memory has stuck with
me. Is this true or was this someone having fun with me? (Jonah, London,
England)
A:
I’m afraid someone was teasing you. Chameleons don’t pay much attention to the
color of their background. They change color to express a mood to other
chameleons — dark with rage — or in response to environmental changes — such as,
light intensity or temperature.
 A chameleon, ignoring his background color. [University of
Georgia]
Further Reading
WonderQuest: How and why chameleons change color
The
Chameleon community
(Answered Aug. 6, 2004)
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