Explanation of Bipedal Locomotion and Some Experimental Verification

James Howard jmhoward at sprynet.com
Sun Dec 6 17:32:35 EST 1998

Bipedal Locomotion and Some Experimental Verification

James Michael Howard
Fayetteville, Arkansas, U.S.A.

Testosterone is higher in human males and females than chimp males and
females, respectively. I suggest that this, and two other hormonal changes,
are the driving forces of hominid evolution. However, I think increasing
testosterone was the initiator of the divergence of hominids and pongids.
(For purposes of this treatise, when I discuss testosterone, I include
dihydrotestosterone.)  It is known that testosterone is the activator of sex
drive in males and females. Therefore, increases in testosterone would
increase sexual activity in females and, simultaneously, reduce the
estrogen-dependent labial display because of an increased testosterone to
estrogen ratio.  Coincidental with these changes in display and sexual
appetite in hominid females is another effect of increased testosterone:
reductions in hair.  (To explain this, and it needs to be explained in this
context, I must give you a little more of my theory of hominid evolution,
which may be read briefly at http://www.naples.net/~nfn03605 on the web. My
supporting references are also at this site.) My work suggests transcription
and duplication of DNA require the hormone, dehydroepiandrosterone (DHEA),
for optimum efficiency. (Some of you will be familiar with cell culture;
growth of cells in culture will occur, but only very slowly. Cells in
culture increase growth tremendously if serum is added to the culture
medium. DHEA is the most abundant steroid hormone, by far, in serum.)
Therefore, all tissues compete for the supply of DHEA. Testosterone has
"target tissues," because these tissues produce receptors for acquiring
testosterone. Upon entering the nucleus of these tissues,
testosterone-protein complexes initiate a transcription cascade that
produces the effects of testosterone. For this transcription cascade to
occur, according to my theory, DHEA must be provided for optimum
transcription. Therefore, when testosterone is secreted, testosterone
directs the use of DHEA for testosterone target tissues. This pushes the use
of DHEA towards use for these tissues. This increases the competitive edge
of these tissues for a limited supply of DHEA. Since testosterone may
increase competition for DHEA for testosterone target tissues, less is
available for hair production. Men of higher testosterone exhibit baldness
more than those of lower testosterone; the ratio of testosterone to DHEA
will produce the exceptions to this rule. That is, a man of very high
testosterone and high DHEA may retain his head hair.  As a rule, however, it
is testosterone that causes baldness.  Therefore, an increase in
testosterone in early hominids simultaneously initiates increased sex drive,
aggression, and reduced hair. One change starts all of this, and
testosterone will increase itself because of increased sex drive and
aggression in competition for females.

The foregoing paragraph explains the scenario that resulted in the extreme
dimorphism of the early hominids. The males were first affected by this
phenomenon. The larger males reproduced at the expense of smaller males.
Breast development is directly tied to the production of DHEA, and, in
females, DHEA is directly tied to ovarian function.  (Again, supporting
citations are at my website.) This means that the breast can also signal
sexual maturity.  Since females also compete for males, the breast developed
as a sexual signal in these hominids that were losing their hair and genital
sexual displays, and increasing in sexual drive. The musculature is a
testosterone target tissue. The increases in testosterone increased the
strength of the legs, and most importantly, the strength of the gluteus
muscles. "Its [gluteus maximus] large size is one of the most characteristic
features of the muscular system in man, connected as it is with the power he
has of maintaining the trunk in the erect posture." (Gray's Anatomy, 1966,
page 500)  The females eventually began upright bipedal locomotion, because
the ones that could do this and display their breasts were more attractive.
The human breast is the only breast used for sexual attraction. All this
requires is increased strength in the muscles of primates used for upright
bipedality. Over many years of increasing testosterone, these changes in
musculature would be followed simultaneously with plastic changes in the
bones, hence, fossils. These phenomena occurred prior to the development of
the large brain.  That is, upright, bipedal locomotion occurred as a result
of increases in testosterone in early hominids without any pressure to
develop larger brains.   I suggest increases in testosterone in hominids
over time were directly involved in reduced hair, reduced labial display,
and increased importance of the female breast as the primary sexual
attractor, then increased strength of muscles used for upright stance, all
of which combined to produce upright, bipedal locomotion.

Experimental Support

My explanation of biped locomotion suggests that increased testosterone in
hominids reduces hair and DHEA increases hair.  Chimps produce more DHEA,
but less testosterone; chimps produce much more hair.  This is also found in
humans.  DHEA is significantly increased in women who exhibit increased body
hair growth (Contraception 1993; 48: 47).  Also, increased body hair of
Caucasian men compared to Chinese men is due to significantly increased
levels of DHEA, while testosterone levels did not differ (J Clin Endocrinol
Metab 1991; 72; 1242).  So, if I am correct that hair is increased by DHEA,
but reduced by testosterone, then reducing testosterone should increase hair
production.  (The effects of testosterone on hair growth is due to its
conversion product, dihydrotestosterone.)

Finasteride reduces conversion of testosterone into dihydrotestosterone, so
finasteride reduces the effects of testosterone.  In one study of the
effects of finasteride production on numerous hormones, the conversion of
testosterone into dihydrotestosterone was reduced 60% after three months
treatment while there was no significant change in DHEA (Steroids 1998; 63:
208).  In two studies of finasteride in macaques, finasteride reduced the
production of dihydrotestosterone and this increased hair production (J Clin
Endocrinol Metab 1994; 79: 991 and J Clin Endocrinol Metab 1992; 74: 345).
The brand name of finasteride that is used in human males is “Proscar.”
Proscar is currently being marketed as an anti-balding remedy.

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