Sweating is a dryland, not an aquatic adaptation in humans.

From: Philip Deitiker (Donevenask_at_worlnet.att.net)
Date: 01/15/05 

Date: Sat, 15 Jan 2005 05:23:23 GMT

"jae@ucdavis.edu" <jae@ucdavis.edu> says in
news:1105758055.341346.113630@z14g2000cwz.googlegroups.com:

>
> Algis Kuliukas wrote:
>> Bob Keeter wrote:
>> > <jae@ucdavis.edu> wrote in message
>> > news:1105724402.173946.146980@c13g2000cwb.googlegroups.com...
>> >
>> >
>> > > In this light, how valid is your statement that sweating
>> > > "wastes
>> water"
>> > > when a primate who lives in a habitat that is rather arid
>> > > for
> large
>> > > portions of the year shows similar levels of
>> > > thermoregulatory
>> sweating?
>> > >
>> >
>> > I think that your little friend is very conveniently
>> > forgetting a
>> discussion
>> > that he and I had a while back in which he agreed that
>> > sweating
> ONLY
>> > makes sense, from an evolutionary standpoint, in a dry
>> > environment with ready access to DRINKING water. Apes that
>> > live in the trees, with ready access to water, plenty of
>> > tropical heat, but a quite
>> humid
>> > environment do not sweat all that much. But humans do. . . .
>> > .
>> hmmmmm.
>> >
>> > Is that perhaps one of those "tiny little troubling issues "
>> > in the
>> theory?
>> >
>> > 8-) But those kinds of holes close with time and
>> > forgetfulness I
>> guess. ;-)
>> > Or perhaps just ingenuous self-serving memory and a dearth of
>> > intellectual honesty.
>>
>> I've been arguing (with Jason as I was with you, Bob) that
>> humans are largely terrestrial animals that happen to swim
>> better than chimps. Water has acted as an agency of selection
>> is our evolution more than their's. Did you miss something?
>> I've been arguing for that for
> years.
>>
>> Yes, sweat cooling makes sense in an arid habitat where there
>> is
> access
>> to drinking water. But an even better way of cooling is to go
>> for a dip, right? And if there's no drinking water, sweat
>> cooling is a very bad idea. So, the best place for such a
>> hominin to have evolved is in
> a
>> water-side habitat where it can go for a dip, ideally, but
>> sweat to keep cool for a limit amount of time if it has to.
>> There's no contradiction.

Animals migrate to where they can survive in competition with other
animals. Humans live in the namib. very few other animals can live in
the Namib, most of the animals that live in the namib have specific
adaptations for living in the namib.

Humans are one of the very few species of animals that can live and
cross the sahara. The only other animals that can do this have
specific desert adaptations.

Humans live in the australian outback most of which is desert. Most
of the few species of animals that live in the outback have specific
desert adaptations.

Ego humans have adaptations for surviving in places where other non-
desert animals cannot survive.

What adaptations to the namib desert do humans have.
1. They sweat, in a dry highland climate with hot daily temperature
sweating is a very effective way of keeping a heat producing brain
cool.
2. They also have little hair which increased air flow around the
sking which increases the efficacy of sweating.
  Therefore hairlessness and sweating are desert adaptations. Do the
!kung where cloths. The !kung are one of the few peoples left on
earth which wear fewer cloths. Therefore clothing, as a surrogate for
hair is not used by adaptive namib tribes.

The logic which you present for sweating, Algis, is internally
inconsistent and circularizes itself over a portion of the argument
which assumes that while there is insufficient water for growing
succulent plants, or supporting vast grasslands, that desert dwelling
peoples have not enough water to support daily perspiration, at that
efficient perspiration as seen in !kung. That assumption is wrong, be
fore such tribes can surive we must assume they secured persistent
sources of water for survival and as a result no longer have a need
for opulent sources of water like lakes or ponds, etc.

 The !kung are namib desert dwellers, like a coyote, who still laps
from a pond or a small stream, or a hawk who does the same, the basic
drinking water needs of many desert animals establish both range but
is usually not self limiting in terms or the water source. Typically
evaporation consumes more water than drinking will for isolated steam
fed pools in the desert lowlands. Therefore the supply of water is
not the problem with desert dwelling humans. The problem for desert
dwelling animals is extending supply. Camels store water, other
animals like elephants can goes for weeks without water, some
antelope can derive water from seeds and succulents they eat.
Humans have adaptations.
 1. They alter water usage over time to become more efficient water
users in the desert environment. This reflects on some general
physcially adaptive feature of humans that has been under desert
selection in the past. Ergo part of the common evolutionary history
of humans.
 2. The learn desert plants and tubers that are reservoirs or water.
 3. The learn to adapt gord fruits and eggs from birds, and skins as
a means of carrying water.
 4. They learn to travel in the morning and evening a and take
shelter in the heat of the day, resting.
 5. They learn to observe other desert animals, particular water
sensing animals and learn where obscured sources of water are.
 6. The learn to dig and reopen sources of ground water up and keep a
collective memory of where these are so they cen reuse these in times
of drought.

 Summary, humans can live in desert and semi arid climates (fact).
The earliest branching of humans shows a people who are greatly
adaptive to desert (fact) other desert dwelling people around the
world branched independently (deduced). Humans can adapt better than
most generally adaptive animals to the desert (fact, exception being
wolves, even so there are specific subspecies). Humans have desert
adaptations (1) immediately sweating to stay cool (2) long term
physciological changes for more effective sweating (3) Utilizing
water sources like desert adaptive animals (4) learning and
remembering critical spots for water use, as desert adaptive animals
can find. Conclusions, humans are better at atapting to deserts
relative to most other land animals. There is no inconsistency in the
adaptation.

  If you give humans the same amount of water, place one group in the
desert with shade at one temperature, then place another group next
to a swamp at the same temperature, as long as the desert living
humans have adequate water they will be more comfortable than those
living in the sweltering swamp. Human sweat system is far more
effective in the desert than in a swamp. Coming from someone who
lives in houston and was born in west Texas. It gets hotter in
southwest texas in the summer time. The car I had, had no air
conditioning, as long as the humidity was low it was tolerable even
up to 102'F (39'C). In houston when the temperature is about 85 on a
typical day of humidity it starts feeling unconfortable. around 96'F
(36.5) the temperature is practically unbearable. Even on a bicycle
traveling at 15 MPH in the shade there is insufficient evaporation in
summer humidity (80-90%) to keep the body cool. Sweating is rather
ineffective around a swampy lowland location of high humidity. It is
most effective at higher elevations.

> There's no explanation either.

Right. He takes what is an obviously desert adaptation and tries to
do a 'snake oil sales' treatment and massage it into aquaticism.
Shameless as a matter of fact.
 
> The ready availability of a watersource is quite a different
> thing altogether from "explaining the major differences between
> humans and apes" as a result of getting in the water. What is
> absent from your explanation is why there is this pressure to
> stay cool in a creature who is around water often enough to
> "take a dip" that isn't seen in other lineages.

Sweating around a swamp is not a substitute for taking a dip. In
order for sweating to be balancing adaptation for a 'dipping' species
that species would need to be able away from the humidity of the
lowland during a nominal period of time. In most places in africa
this means traveling more than 200 miles. It is not realistice to
believe that during an aquatic phase humans traveled 200 miles to a
dry location as to make sweating efficient. Therefore if dipping and
sweating evolved at the same time, then it means one human isolate
was evolving toward more sweating and thus a desert dweller away from
dipping pools, while the other was utilizing dipping. This is not
aquatic ape, but mosaic ape theory. Algis cannot have his cake and
eat it to, sweating is ineffectual in a swamp, it is most wasteful in
a swamp. It is the most effective adaptation in a desert.

> The pressure to
> stay cool is greatly minimized if water is around, but somehow
> you're arguing that a rather pronounced mechanism that manages
> to give us an ability to operate at higher temperatures than a
> whole host of creatures somehow evolved in this environment
> where the presences of water minimized the stress that gave us
> this adaptation.

What I would say to Algis, come to Houston next summer, it is in
essence swampland, sweating is not a very effective means of staying
cool in a high humidity environment, particularly once outside
temperature approaches or exceeds body temperature.

> It's a peculiarity at least if not an actual
> contradition.

It is an actual contradition. Sweating relies on the differential
between the vapor pressure of water at a temperature and the vapor
pressure of water at body surface temperature relative to the maximum
vapor pressure of water (100% humidity). The closer the outside
temperature is to body temperature, where the humidity is close to
100%, the efficacy of sweating drops. These conditions converge in
equitorial swamps. The maximum rate of cooling by sweat is in a
condition where the temperature is high but humidity is low, where
the dry air can adsorb lots of water per unit of air. Breezey
condition like on an arid plateau are best. Stagnate air such as
around a hot equitorial swamp under the doldrums are about the least
effective place for animals that stay cool by sweating.
  If sweating is an adaptation for swamps, based on living in a
'swamp' I can say that this adaptation is only effective for about 5
hours a day, when in the evening the sun stops driving water off the
surface and relative humidity ebbs off slightly. During the rest of
the day sweating is simply a miserable consequence of a ineffective
cooling system for an animal that really should be in the cool shade
taking a nap. (Remember San Jacinto!) 

-- 
Philip
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