Phil Nicholls (firstname.lastname@example.org)
Sat, 29 Jul 1995 03:55:53 GMT
Ralph L Holloway <email@example.com> wrote:
>On Sun, 23 Jul 1995, Phil Nicholls wrote:
>> Hence the neurological controls over eccrine sweat allow better
>> regulation (control) of the sweating process. The mechanisms is
>> present in apes and monkeys but is evoked only in response to extreme
>> heat stress. Hominids modified this existing system when the
>> enlargement of the brain required better thermoregulation. Under
>> this scenerio, Australopithecines would have been more like gorillas
>> and champanzees in terms of sweating.
> Thanks to Phil for re-doing this summary. I really think the nervous
>sytem factor is quite important. I do hesitate to accept your reasoning
>about hominids modifiying the existing sytem as a consequence of brain
>enlargement, and I guess we all know that the "radiator Hypothesis",
>while an interesting speculation well worthy of much more research is
>still controversial, and the peer commentary from the Behavioral Brain
>Sciences article make clear. Whatever the reasons, it would be useful to
>reiterate just exactly as possible how human beings differ from the
>large-bodied apes in thermoregulation processes. How secure is the
>comparative data on numbers, ratios, of the glands, reactions to dew
>points, etc., and is there a good body of information of just
>within-species variation of these variable for Homo sapiens?
Most of my information about gland ratios came from the source Elaine
Morgan cites in Scars of Evolution (Sokolov, Mammalian Skin). It is
not a heavily researched area.
I was not offerring a defense of the "radiator hypothesis." Dean Falk
is not the only person to make a connection between brain enlargement
and thermoregulation and the "radiator" that concerns me here is the
skin and not cranial blood flow. Of course, it is speculation and
nothing more to suggest a relationship between the evolution of
sweating and the evolution of the brain.
> I ask this last question because it is a logical place to begin any
>comparative study. Is the range of variation so great (or not) that ape
>values in anyway overlap with our own. Iask, because Elaine Morgan's
>recent post seemed to imply that there were many publications and
>advances in our knowledge of these things in the '80's and 90's. I don't
>have that impression.
I don't either.
> I am aware that the change in body size and proportions between
>Australopithecus and Homo (as studied through the form of the rib cage,
>particularly by Leslie Aiello) might provide an alternative to the
>Radiator Hypothesis, as it signals a possible reductioin in the size of
>internal organs, which are also very high in terms of metabolic demands,
>the implication being that the brain could afford enlargement without
>building a "new" system of venous drainage.
That's an interesting idea, but since the interesting thing about
sweating is that it allows a finer degree of homoeostaic regulation to
come into play.
> Ralph Holloway
Phil Nicholls firstname.lastname@example.org
"There is a grandeur to this view of life, with it's several powers, having
been originally breathed by the Creator into a few forms or into one; and
that, whilst this planet has gone cycling on according to the fixed law of
gravity, from so simple a beginning endless forms most beautiful and most
wonderful have been and are being evolved."
[Last sentence from _On the Origin of Species_, by Charles Darwin