September 11, 2003
A: FROM MENTOR LEE PELLEGRINO-GENSEY IN NJ
I'm not sure if anybody knows exactly why there is less pigment on palms and
soles of feet, but I would think that somewhere along the line it gave
humans and their ancestors an evolutionary advantage. A random mutation
that appears in a population can either be beneficial, allowing the
individuals carrying that trait to survive long enough to pass on their
genes, or harmful, causing the carriers of the trait to die out before
passing along the gene, or neutral. You can imagine many scenarios that
could make lighter palms and soles beneficial and allow better survival of
those who had them over those who didn't. It could be something simple like
the white fur under the tail of some deer that shows as a danger signal when
they run from harm, alerting other members of the herd. Maybe lighter palms
made communication by hand signal easier to follow in the pre-speech days of
our ancestors and kept aggression levels down - if you could raise your hand
in friendship or submission and be easily spotted, it kept you out of lethal
fights. It could simply be that the genes for hair and the genes for
pigmentation are linked (the neutral scenario) - note also that we don't
have hair on our soles or palms but we do everywhere else, even if it's fine
and hard to see (or missing on some people - your uncle might have hair on
his ears where most people don't!). You can probably think up other
possible reasons - challenge your friends to come up with some. Look into
signaling, submission, and aggression in other species and see how color or
gesture or posture can be used in each case. In general, a trait like
pigment or shape or behavior sticks around because it gave an individual's
ancestors an advantage or was neutral and came along with something that
gave an advantage. Darwin rocks!