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Hominid Brain Size: Testosterone, DHEA, and Melatonin
James Howard (phis@sprynet.com)
Fri, 01 Nov 1996 22:35:37 GMT
ahimoe@net66.com (Albert Himoe) wrote:
>In article <557c3n$bg2@juliana.sprynet.com>, James Howard
>(phis@sprynet.com) writes:
>> 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.
>Then why do the hominids in Africa have the smallest brain size? Or,
>do you means that the losers colonized the world, and the winners
>brains shrank?
>--
>Albert Himoe
>email: ahimoe@net66.com
James Howard responds:
Thank you for your question. I will attempt to answer your question as briefly
as possible; I refer you to my relatively brief explanation of this at
http://www.naples.net/~nfn03605 on the web. For sake of brevity here, you will
find citations supporting this explanation in my article there. (If you try to
reach my website, please be patient; I have been unable to reach it for days.)
My work suggests that the hormones, melatonin and DHEA, as well as testosterone,
are involved in increases in brain size. However, for melatonin and DHEA to
exert effects, they have to be increased. DHEA is known to increase metabolism;
it does this by stimulating mitochondria. Hominids that there driven away from
the equator and into colder environments would have an increased survival rate
if they produced increased DHEA. In vitro, DHEA stimulates neuronal survival
and differentiation. Hominds that produced more DHEA could survive colder
environments and produce bigger brains. My work also suggests that melatonin
acts in a cycle that stimulates DHEA. Melatonin production increases as light
decreases. Hence, movement away from the equator will stimulate both melatonin
and DHEA. This will increase the brain size in hominids forced away from the
equator.
The brain is full of testosterone receptors. It is my theory that testosterone
stimulates use of DHEA for "testosterone target tissues." That is, I think
testosterone stimulates the absorption of DHEA. (My basic principle is that
DHEA optimizes transcription and replication of DNA.) Hence, increases in
testosterone will increase use of DHEA for the brain and increase its size.
Humans, therefore most likely hominids, produce more testosterone than chimps.
I suggest this is why hominid brain size increased in Africa.
The brains of the early hominids were larger, but not significantly larger, as
that found in later hominids. The hominids that remained in Africa did not have
the effects of DHEA and melatonin to stimulate brain growth. Hence, the
increase in testosterone of these groups affected their brains only slightly,
but the increased testosterone directly affected their bodies. You see, the
body is also full of testosterone receptors. Now, my work suggests all tissue
compete for DHEA. The brain competes with the body. In this group, the brain
did not increase in size to a large extent so the increases in testosterone
affected the body in increased amounts. I suggest this is why the robust
Australopithecines developed. Their brains did increase in size, but their
bodies increased much moreso.
Hominids that were driven away from the equator, I suggest, benefitted from the
increases in DHEA and melatonin. That is, their brains benefitted. As the
cycle of breed and feed cycles continued, testosterone also increased. This
increased the absorption of DHEA in individuals who were producing more DHEA.
This combined to make for bigger individuals with bigger brains. That is, DHEA
and testosterone both increased.
This is how I explain Neandertal. That is, Neandertal is the result of being
"position locked." The hominids that ended up in Europe became locked in place;
they could not easily run from the effects of testosterone. In the severe cold,
their DHEA also increased. That is, testosterone and DHEA both increased in
very large amounts at the same time. If you have been following my argument,
you should know that very large increases in testosterone and DHEA should
produce a hominid of very large size with a very large brain. Since I have
discussed the effects of testosterone on teeth in this newsgroup, I will add
that this same situation should produce very large teeth. Now, I will not go
into further detail at this time, but this is an explanation of Neandertal that
is directly drawn from the same mechanism that produced all hominids.
My theory also suggests that the brain and body compete for DHEA. The larger
the brain is, the better it can compete for DHEA in the blood. (The larger the
brain, the more surface there is for absorption of molecules.) Hence, as the
brain became bigger, the body became smaller. The bigger brain caused the body
to become more "gracile." This is why the hominid line evolved into the gracile
form.
James Howard
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