Re: AAH: humans long-distance runners?

Gerold Firl (geroldf@sdd.hp.com)
1 Dec 1994 13:20:38 -0800

In article <jlittle-3011941644580001@47.69.129.57> jlittle@bnr.ca (Jim Little) writes:

>I just have to jump in here, all sweating buckets does is remove buckets
>of essential moisture from the body which must then be replaced. Water
>that runs off the body in rivers does not cool any better than a very thin
>film.

True. But that is exactly what humans do; we generate a thin layer of
moisure all over our body. Of course, some does drip-off, and that is
wasted, as you say, but most of it evaporates, which results in cooling.
Our cooling system is not optimally *efficient*, just extremely
*effective*. It rejects huge amounts of heat. A god, or an engineer, would
try to design a more efficient system; evolution just produces one that is
effective.

>A dog (and many other animals) can cool its entire body just by
>panting (with associated cooling by evapouration present in its
>exhalations).

At 100 degrees fahrenheit a dog can cool its entire body by panting, if it
lays quietly in the shade to minimise the amount of metabolic heat
produced. A man can run at that temperature.

>The human system of sweating is very wasteful and poorly
>adapted to its function.

Not really. It is somewhat wasteful, but very well adapted to its function.
It gives us a capability which no other animal can match.

>I can give you a reason for an aquatic hominid to sweat as prodigiously as
>modern humans do, to eliminate excess salt from the body.

I haven't read morgan, but from the comments I've read it appears that she
doesn't mention that the human sweat ducts have a salt-recovery system
which actually re-absorbs salt from sweat as it is secreted from the
sub-dermal glands and passes to the surface of the skin. (See Guyton,
_Human Physiology_).

-- 

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Disclaimer claims dat de claims claimed in dis are de claims of meself,

me, and me alone, so sue us god. I won't tell Bill & Dave if you won't.

=-=-=-=-=-=-=-=-=-=-=-=-=-=----   Gerold Firl @ ..hplabs!hp-sdd!geroldf