Re: Holloway/Morgan
Gerrit Hanenburg (ghanenbu@inter.nl.net)
Mon, 31 Jul 1995 18:09:48 GMT
Elaine Morgan <Elaine@desco.demon.co.uk> wrote:
> SWEAT.
>WHAT I SAID IN SCARS.
>This century's ace expert on primate skin, Wm. Montagna, said that
>man's unique (as he believed) eccrine sweating is so disastrously
>inefficient that it must have evolved originally for some other
>purpose. It is recklessly and pointlessly wasteful of water and salt,
>both scarce resources on the savannah. Their depletion can cause heat
>cramps, dehydration, and death. Most hot-climate mammals are
>parsimonious with their (apocrine) sweat; if their salt balance is
>threatened they may switch to sweating potassium chloride instead of
>salt.Our system behaves as if the two things in unlimited supply in
>the environment were water and salt.
Losing water and salt through sweating may be inefficient as far as water and
salt balance are concerned but sweating is very efficient in
thermoregulation.Loss of water and salt might be a trade-off between staying
cool and maintaining an optimum water and electrolyte balance.Water and salt
can be restored but you have to get rid of excess heat no matter what because
hyperthermia is as deadly as severe dehydration.You give the impression
humans are losing buckets of water a day but from my physiology book I get
the following data:loss of water via sweat at normal temperature:200
ml/day,loss at high temp.:1500 ml/day.That's not an astronomical amount.
Under normal circumstances you produce 1400 ml urine/day (mostly water).That
would make urineproduction wastefull too.(and thus disastrously inefficient?)
(if you loose water by sweating, your kidneys will partly compensate by
producing less but more concentrated urine)
The savannah is not a desert and early hominids were probably rather
mobile.So going to the waterhole may have been daily business.
(as in so many other savannah animals)
>He didn't speculate on what the original purpose of eccrine sweating
>was. So I had a go. Connecting it with the similar pointlessly-profuse
>shedding of tears, I thought it might have been another reaction to
>"too much salt" (again given the unprovable premise that tears and
>sweat were once hypertonic)
But mammals already have a way of dealing with electrolyte imbalance:kidneys.
It seems to me more likely that the primary advantage of sweating was
thermoregulation (as it is today) while loss of salt via sweat may have been
a "spandrel" (a side-effect:instead of being an adaptation it's an
exaptation)? Biologically it's very difficult if not impossible to sweat pure
water.
The phrase "profuse shedding of tears" seems to me an exaggeration.Unless you
suffer from severe affective incontinence or a foreign particle has taken
residence on your cornea nobody is shedding tears profusely.
The loss of water and salt via tears is negligible even if they are
hypertonic.
Gerrit.
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