Re: chimps stronger than humans

First, thank you for you thoughtful reply.

I will answer these as a group; going back and forth just confuses matters;
well it confuses me when I read a mixed up post / response thread. My post
and your responses are all below this for reference.

No, I do not say "cold equals increased growth of brain and body." I say
that higher DHEA allows living in the cold and extra DHEA increases growth
of brain and body. I also suggest that situations that increase
testosterone, especially when boxed in, may cause an increase in overall
size. This is how I explain the very large gorillas and orangs that
occurred in the tropics. The very large difference in males and females in
these groups is due to the increased male testosterone. This increase
occurs without the effects of cold causing increased DHEA. With that in
mind, let us look at Boxgrove Man. Boxgrove Man was found in England, a
peninsula at the time. I think it is very possible that Boxgrove Man
increased size may be due to the same effect of a group being relatively
isolated which increased testosterone and there was enough cold to select
for DHEA. ...so Boxgrove Man became very large with the combined effect of
testosterone increase and DHEA increase.

The Bergmann rule refers to animals actually being smaller farther north. I
explained this effect by first suggesting the large mammals got big as
selection for DHEA occurred. I then suggested that living farther north
will require more DHEA for warmth generation. ...less DHEA for growth and
more for warmth reduces overall growth. Boxgrove man lived in "relative"
warmth and later, Neandertal, lived more during the ice ages so I suggest
their smaller stature may be due to the use of some of their DHEA for
warmth, so Neandertals were smaller. Again, I think the tropics produced
some large animals as a result of increasing testosterone, that is, cold was
not required.

Chimps and humans split off together. I suggest this is due to the increase
in maternal testosterone which can be seen as less of a difference in size
between male and female. Human evolution is driven by the appearance of
increased maternal tester. Females gained in size rather than males being
reduced in size during human evolution. This is why the male to female size
difference was reduced. According to what I have posted here, increased
maternal testosterone increases exposure of the fetal brain to maternal
testosterone, which increases brain androgen receptors. This increases use
of DHEA by the brain at the expense of body because of competition for
available DHEA. (If one lives in the cold and gets bigger and moves north,
the competition for DHEA between growth and warmth is due to the same
competition.) So chimps differ from gorillas and orangs in this way. This
did not occur in gorillas and orangs but together in the common ancestor of
humans. This is why the chimps did not follow the pattern of gorillas;
chimps' brain compete more for DHEA at the expense of the body.



"Lee Olsen" <paleocity@xxxxxxxxxxx> wrote in message
news:8a1605f8-c3fb-49b0-9005-8769d5f2d9f9@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Apr 10, 7:56 am, "James Howard" <jmh.anthropogeny....@xxxxxxxxx>
wrote:
In reference to: > How does Neandertal, and Cro Magnon for that matter,
fit
into

this framework? Both had very large brains in hyper-robust bodies."

I think living in cold environments requires extra DHEA. The individuals
who could not provide sufficient DHEA to provide resistance body
temperatures, died. Extra DHEA would provide increased growth and
development of the brain and body. (The next text is intended as further
explanation.)

Your whole scenario is based on a false premis, i.e., cold equals
increased growth
of brain and body. Tom has made an excellent point, he just did not
go back
far enough in time for his example. The Boxgrove Man, Homo
heidelbergensis,
was bigger, taller, stronger, and also had a very large brain, ca.
1200 cc. He lived
in a temperate interglacial climate, proven by lions and spotted
hyenas. From then
on Western European Neandertals got smaller (with St. C being a real
whimp in size,
being one of the last), so this makes your prediction of colder equals
larger just
backwards of what actually happened. Cro-Mags were another later input
from Africa
and the same cycle repeated itself.



This principle may also explain why ice age animals grew
larger.

Wrong again, Africa also lost some large Pleistocene animals during
the extiction
process.

However, if a species is in a position whereby testosterone may
also be selected, then this increased testosterone may amplify the effects
of cold-induced DHEA. Hence, the Neandertals exhibited exaggerated sizes,
produced, I suggest, by the early groups being concentrated in specific,
cold areas.

Nope, Neandetals favored southern, warmer, climates when available,
they
dealt with reindeer and mammoths only when they had to.


Concentration, I suggest, causes selection for testosterone.
Since gorillas and orangutans are large and live in the tropics, I would
think their increase in size is more of a testosterone effect.

Then after chimps and gorillas split, they BOTH live in temperate
warm
climates, why did chimps not follow your predicted pattern?

If anyone
responds to this, they will probably mention "Bergmann' Rule." If an
animal
increases in size due to extra DHEA triggered by cold and reaches a limit
in
DHEA production, then the extra DHEA is used for warth at the expense of
size. So animals farther north become smaller as a result.

Chimps and H h demonstrate that you are not correct in your
reasoning.


(Now, to answer
another question likely to be generated by the foregoing, I think chimps
are
smaller than gorillas and orangs due to increased testosterone in the
"common ancestor" of chimps and humans.

But neither g/o/pan lived in a cold climate, you have it just
backwards.
Tall humans and short ones lived in both warm and cold climates.

That is, the female in the common
ancestor increased in testosterone which exposed the brains of their
fetuses
to increased testosterone. This began the process of producing a brain
which competed better for available DHEA. Hence, chimps and humans produce
more testosterone than gorillas and orangs but are smaller.) James Michael
Howard

But above you claimed "I think living in cold ....growth and
development of the brain
and body"
According to this reasoning, gorillas/orangs should also have larger
brains
than chimps, and they don't. You have a non-starter hypothesis that
explains nothing.




.

Relevant Pages

  • Re: chimps stronger than humans
    ... I think living in cold environments requires extra DHEA. ... development of the brain and body. ... Then after chimps and gorillas split, ...
    (sci.anthropology.paleo)
  • Re: chimps stronger than humans
    ... I do not say "cold equals increased growth of brain and body." ... that higher DHEA allows living in the cold and extra DHEA increases growth ... are large in cold climates it is because of DHEA. ... these groups is due to the increased male testosterone. ...
    (sci.anthropology.paleo)
  • Re: chimps stronger than humans
    ... available DHEA. ... I think the brain evolved during mammalian evolution to ... I think primates evolved because of increased use of DHEA by the ... dramatically increased maternal testosterone which may be "seen" when female ...
    (sci.anthropology.paleo)
  • Re: chimps stronger than humans
    ... all tissues, especially the brain. ... available DHEA. ... I think primates evolved because of increased use of DHEA by the ... dramatically increased maternal testosterone which may be "seen" when female ...
    (sci.anthropology.paleo)
  • Re: chimps stronger than humans
    ... I think living in cold environments requires extra DHEA. ... if a species is in a position whereby testosterone may ... This began the process of producing a brain ...
    (sci.anthropology.paleo)