Natural Science Forum / Biology / Biology / January 2005

The idea that there is a complete transition from
black to white with no shades in between, is a
phenomenon intrinsic to American history, if not
the Sahara desert.  Basic selection factors at
least as far as I have heard, with respect to
skin color, tend to fall under skin cancer,
vitamin D production, and possible camoflage
during hunting or gathering.

The amount of near ultraviolet radiation that
falls upon the earth, tends to depend relatively
heavily upon the angle that the sun is in the
sky.  A small level of cloud cover will only
scatter and diminish it very slightly, however
a heavy level of cloud cover will often
reduce it to a greater extent.  Also, snow
glare will tend to reflect ultraviolet
radiation off the ground and also magnify the
level of ultraviolet radiation presented by
the environment.  The sun will of course,
produce little ultraviolet radiation at
night.  I am not sure what level of UV
output that a campfire will put forth.

If the universe or at least human civilization,
were not produced only several thousand years
ago, the following from archaeology and
paleontology could also probably be inferred.

Man probably left Africa for at least the
southern part of Eurasia about 1 to 3
million years ago.  There might possibly
have also been some genetic interaction
within the species over time in the
various regions where humans were
present due to the physical migration
of the life form throughout time
from place to place.

Man did not colonize the most northern
parts of Eurasia, at least for during the
highth of the ice ages, if not the
interglacials, until at least the past
50,000 or so years, or only slightly
longer.  Lack of extremely ancient evidence
for man in North and South America might
at least possibly indicate this.

Man did not go on long ocean voyages
until the last 50,000 to 70,000 years
or so.  Lack of extremely ancient
evidence for man in Australia might
tend to indicate this.

Hairlessness might tend to possibly
favor darker skin with regard to
skin cancer.  However, lighter
skin will be able to produce more
vitamin D to protect against rickets,
for those early humans who had not
inferred the immediate idea, of possibly
eating animal livers in order to
compensate.

A thick cotton shirt will produce
about the same level of blockage
of ultraviolet light as relatively
dark skin color will.  Probably
some animal skins or furs would
cut out ultraviolet light
even more.

This produces the question with
regard to how long ago humans
started wearing clothing in northern
climates to protect against heat
loss in winter, and possibly
provide at least a temporary
immediate short term protection
against some, less powerful animal
bites in some areas.

Shoes will help to protect the
feet of humans against sharp
objects while running, however
a heavy skin might also reduce
the speed of a human while
running, and decrease protection
against overheating during
periods of high exertion, unless
they are shedded (which if they
were not highly treated skins,
might also, still be eaten by
predators if one does not return
and recover them fast enough).
Another fundamental problem with
wearing at least animal skins, is
the potential for attracting large
predators from their smell if
they are not treated in some
fashion.

If a human were to wear a large
amount of thick clothing, this
would only leave part of the
body available to to produce
vitamin D from sunlight, disposing
the wearer to possibly become more
susceptible to rickets over time.

The question exists, with regard
to how long, that might have presented
an additional selection pressure upon
humans in northern climates, and what
effects that might have had
upon human physiology among its
different variants.  How far
back did clothing go, within
the archaeological and
paleontological record, as
we now know it?