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Why Testosterone Increased in Humans (Re: Hair loss and Sweat glands ...yes, testosterone)
James Howard (phis@sprynet.com)
Sun, 22 Sep 1996 19:56:13 GMT
John Waters asked Sept. 21:
"Now that you have completed the physiological explanations, all you
have to do is to explain why the changes in testosterone level only
applied to human ancestors, and not to the ancestors of any other
primate, or mammal."
James Howard responds Sept. 22:
I suggest that hominid evolution is the result of increases in
testosterone in hominid males and females. This increase in
testosterone resulted first in loss of hair, increased female sexual
activity, and a change from genital to breast sexual display; all of
which resulted in bipedalism. Further, this resulted in later changes
in the hormones, DHEA and melatonin, that participated in the
enlargement of the hominid brain.
The reason "why" this change in testosterone levels occurred is the
same reason why many changes occur in evolution. That is, I suggest a
single mutation occurred in a female animal which ultimately gave rise
to the hominid line. This mutation, in a single enzyme, probably in
aromatase, caused an increase in the ratio of testosterone to
estrogen.
Other than the things I have attributed to this increase in
testosterone in earlier posts to this newsgroup and at my web site,
there are some real changes that I think can be seen in nature. An
increase in testosterone of sufficient quantity should produce an
easily seen adolescent growth spurt. That is, the rise in
testosterone which occurs at adolescence should be characteristically
larger in an animal (human) which produces more testosterone per body
size than other animals. This should produce the adolescent growth
spurt. (My work suggests that finalization of brain growth is
involved in this, currently. However, this is unimportant to this
discussion about bipedalism occurring in hominids, long before the
increase in brain size.)
It is difficult to show the connection of testosterone with the
adolescent growth spurt in females. The literature is fuzzy, but it
is there. If need be, I will use the literature and a lengthy
explanation to show this. For now, consider that testosterone is
higher in human males and females than in chimpanzee males and
females, respectively. In boys the connection of the growth spurt and
testosterone is supported directly. O. Butenandt, et. al., "Mean
24-hour Growth Hormone and Testosterone Concentrations in Relation to
Pubertal Growth Spurt in Boys with Normal or Delayed Puberty," Eur.
J. Pediatr. 1976; 122: 85. "It is concluded that the growth spurt in
puberty is not due to a change in growth hormone concentration but
rather to the increase of androgen [testosterone] production in
puberty."
If I am correct that increased testosterone is the cause of human
bipedalism, and the literature is correct in the connection of
testosterone to the pubertal growth spurt, this should be clear in
nature. Our bipedalism is relatively unique; our pubertal growth
spurt should be relatively unique. This is supported. "Growth of man
differs basically from that of all animals - perhaps except some
species of primates - by demonstrating a pubertal growth spurt."
Gegenbaurs Morphol. Jahrb. 1986; 132: 57.
This difference should be seen in the chimpanzee, our closest
relative. The difference between the female chimp and female human is
the best comparison. "The rise in circulating concentrations of sex
steroids during chimpanzee puberty resembles that in man, with the
exception that serum testosterone concentrations in the male fall into
the lower part of the human male range. ...The usual secondary
characteristics which form the clinical basis of human puberty either
cannot, or have not, been studied in chimpanzees. However, male
chimpanzees do show a spurt in weight growth beginning at 6-9 years of
age which is presumably the result of rising levels of serum
androgens. Surpringly, there does not appear to be a similar
puberty-related growth spurt in female chimpanzees." Journal of
Reproduction & Fertility, Supplement No. 28, "The Great Apes of
Africa," Ed. R.V. Short and B.J. Weir, pages 135-136
I sugest the increase in testosterone in hominid females increased the
probability of extra-ovulatory sexual activity. I have explained in
my other posts to this newsgroup, and at my website, the consequences
of increased sexual activity in hominid females. I suggest this
explains "why the changes in testosterone level only apply to human
ancestors, and not to the ancestors of any other primate, or mammal."
James Howard
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