Skin Color and Location
Name: Phoebe N.
Date: Sunday, October 27, 2002
If we are to believe that skin color is darker near the
equator because of protection from the sun, and, conversely that the
further away from the equator, the lighter the skin because of
necessity to absorb vitamin D....why is it that there is such
a discrepancy between skin color in Scandinavians and, say,
native people of northern Canada or Alaska?
Their ancestry is quite different.
Peter Faletra Ph.D.
Office of Science
Department of Energy
Since the human life span is so long, relatively, evolutionary change takes a
very long time to show phenotypically. These hypotheses of the evolution of
skin color try to answer the question of why dark skin seems to be more
common at the equator and why light skin evolved in temperate areas. Recent
evidence has forced a change in the old idea that dark skin evolved to
protect from skin cancer at the equator. Although that is a benefit of more
melanin, the new hypotheses say that dark skin protects against loss of
folate, a vitamin that we need in our metabolism. In the regions with less
direct sunlight this was not a problem, the new problem was getting enough
sunlight to make Vitamin D. Those with lighter skin could get enough
sunlight to make Vitamin D, making them more fit for their environment. This
process however, took place over millennia. In the meantime humans were
migrating all over the globe, crossing the land bridge from Asia into the
Americas. In today's mobile society humans can "migrate" at will and you
would expect that the populations of various regions would become more
diverse. Humans also now have the ability to manipulate their environment,
i.e., take vitamins, and cover their skin or go indoors to protect themselves
from the environment.
There is are "problems" with your reasoning. I am not criticizing, because
the same question asked in many different forms has been proposed both in
the past and present.
First, it is not evident that people living near the
equator have darker skin because of protection from the sun, or that people
living in northern climates have light skin to increase the production of
vitamin D. Does it? Where are the data? I could suggest that dark skinned
people would produce more vitamin D because their skin is dark, and light
skinned people would produce vitamin D less efficiently because their skin
reflects more sunlight, thus inhibiting the production of vitamin D. That
reasoning is called the fallacy of "correlation and causation". The two
observations may be correlated, but one does not necessarily cause the
other. The skin color correlation also ignores other differences, for
Second, indigenous peoples in Australia and New Zealand are
very dark - skin but do not live near the equator.
Third, we are observing
the global distribution of skin color in a "snapshot" of time in an
evolutionary geological context. Genetic changes generally require a very
long time -- millions of years -- but our demographic observations are only
a few thousand years old, and people can migrate from one region to the
other in a matter of decades -- even hours in the last century -- which is
much too fast for genetics to "catch up". So we do not know that
Scandinavians always lived where they now live, and Africans always lived
where they now lived.
Fourth, there may be more fundamental differences in the biochemistry and
genetics that are operating, and skin color just happens to be a consequence
with no relevance to exposure to sunlight. It is a very complex subject, that
I do not think is well understood at all.
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Update: June 2012