Skin color ...perhaps testosterone

James Howard phis at sprynet.com
Mon Nov 11 06:14:31 EST 1996


Skin color  ...perhaps testosterone

I have suggested that testosterone is directly involved in hominid evolution and
have posted a number of messages here to support my theory of hominid evolution.
Besides my general explanation, these have included the loss of hair, enamel
thickness, increased sweat glands, etc., includinding a demonstration of my
mechanism currently affecting the U.S. population.  A number of posts have
recently been discussing the skin color aspect of hominid evolution.  I
considered applying my theory of DHEA/testosterone to this some time back, but
was unsatisfied with the directness of the support I found.  However, since my
posts regarding the characteristics, mentioned above, support my theory well, I
thought it is time to post the connection of testosterone and skin color since
it fits the pattern of hominid characteristics directly affected by
testosterone.

Since many have ignored my posts and a number have indicated that they do not
read them throroughly, I will put the following citation in context.  I have
suggested that the rise in testosterone in hominids is the mechanism that drives
the population of hominids into new territories.  That is, I suggest that in a
breed and feed situation, testosterone rises and males of low testosterone are
driven away from the group.  I suggest this eventually resulted in the effects
of testosterone, melatonin, and DHEA that resulted in increased brain size.
This means that hominids that stayed in Africa should have the highest
testosterone levels, while those that were driven out have less testosterone.
(Black males produce significantly more testosterone than white males; citation
in some of my past posts.)  This mechanism of low testosterone individuals being
pushed away from the group should occur in each location where populations of
hominids reside.  That is, the rise in testosterone will occur in every
population.  This is what continued to push the hominids throughout the world.
The testosterone levels should be less with distance from Africa.  (This is a
generality since I think this occurs in cycles and may increase in populations
that are "ice-, ocean-, and landloced" so that testosterone is increased
dramatically.  This testosterone, and increased DHEA and melatonin, I suggest,
resulted in Neandertal.)

To return to the point of skin color, it is testosterone that is of importance
again.  The following quotation demonstrates that testosterone and ultraviolet
light (UVL) act synergistically to stimulate epidermal melanin production.  That
is, the more testosterone one has, the more one will produce melanin.  This
means that hominids that were driven away from the equator may have been lighter
skinned, because they produced less testosterone.  During the posts regarding
light colored skin at sci.bio.evolution, it was reported that Eskimos have
darker skin than would be expected if the vitamin D theory of lighter skin is
the only explanation.  I suggest the Eskimos may be an example of a
"position-locked" group that produces more testosterone.  The increased
testosterone in this group may be why they have darker skin than would be
expected.

Glimcher ME, et al., "Organ Culture of Mammalian Skin and the Effects of
Ultraviolet Light and Testosterone on Melanocyte Morphology and Function,"
Journal of Experimental Zoology 1978; 204: 229

"Scrotal skin of black Long-Evans rats and human thigh skin were maintained in
vitro as organ cultures for as long as 14 days, and examined histologically
using the comined skin splitting and Dopa techniques.  Selected rat skin
cultures received testosterone in the culture medium and/or irradiated with
ultraviolet light (290-320 nm UVL).  With increased time in culture, scrotal
melanocytes round up and there is an increase in epidermal pigmentation.  Human
skin behaves similarly; after eight days in vitro human melanocytes also become
rounded, but remain strongly Dopa-positive.  Addition of exogenous testosterone
to cultured rat skin maintains dendritic morphology of melanocytes, but cell
body size is still reduced.  UVL irradiation stimulates melanocytes in rat skin
cultures, maintaining their dendritic morphology and increasing epidermal and
dermal pigmentation.  Cultured skin receiving both UVL and testosterone
illustrates a synergistic effect."

The decreased skin pigmentation of groups living away from the equator may be
due to decreased testosterone.  I suggest this further supports my theory of
hominid evolution.
James Howard




More information about the Mol-evol mailing list