Re: Sweating hominids

Andrew Nowicki wrote:

> Sure. Evaporation cools the evaporating liquid. Evaporation is intensified
> by the flow of air above the liquid. Fur impedes the flow of air, so it
> impedes evaporation and cooling.

Marc Verhaegen wrote:

> 1) Then why do other mammals that are believed to sweat to cool down have
> fur (patas, horse...)?

Fur is useful for other reasons: it keeps the
animal warm at night and keeps some biting
and stinging critters away. For a small animal
the lightweight fur is more practicable form
of protection than thick hide or subcutaneous
fat.

Marc Verhaegen wrote:

> 2) Hairs enhance the surface from with water can be evaporated.

Very short (about 1 mm) and dense fur may act as
sponge holding the evaporating sweat and keeping
uniform layer of the sweat by surface tension
(capillary force). Fur is hydrophilic meaning that
it attracts water and sweat. If the fur is much
longer that about 1 mm, the evaporation of sweat
from the tips of fur fibers cools the fiber tips,
but little heat flows along the moist fibers because
they are long and because sweat flows on the fibers
away from the skin. (The amount of heat flowing through
the fibers is inversely proportional to the length
of the fibers.)

By the way, wolves have sweaty paws which cool
them pretty well due to the contact with cool soil.

Marc Verhaegen wrote:

> 3) Do you have examples of other furless+sweating mammals that sweat a lot
> thermo-actively?

You mean sweat in order to cool. No. I have not
researched this topic. Elephants cool themselves
by waving their ears. Hippos jump into cool water.

Note that female mosquito probes your skin before
she plunges her proboscis into a cavity called hair
follicle -- this is the place where your skin is
thin and easy to pierce. A truly hairless animal
does not have hair follicles, so mosquitoes cannot
penetrate it easily. I guess that the sweat glands
may be weak spots too. It seems that thick, hairless,
sweatless hide is good protection against skin
parasites.

I am too busy now to research this topic, but it
seems that there are no small, warm blooded, hairless
aquatic animals. All the warm blooded, hairless,
aquatic and semi-aquatic animals are giants like
hippos and whales. This suggest that heat loss for
human-size aquatic animal is too high. Another, much
more convincing argument that hairless humans loose
too much heat even in tropical waters is the fact
that we have to wear wet suits or dry suits when
we dive in tropical waters. Scuba divers who wear
lycra suits only really shiver with cold. (I was
a scuba diver long time ago.) THIS IS VERY CONVINCING
ARGUMENT THAT OUR HAIRLESSNESS WAS NOT AQUATIC
ADAPTATION. A hairless, naked human may swim for a
few minutes in tropical waters to cool himself, but
if he stays in the cool water much longer, he will
loose precious calories. If you do not believe me,
spend two hours in a lake dressed in swimsuit only.
When you come out you will be cold and hungry.

Andrew Nowicki wrote:

> Another issue is the ratio of a mass of a hot or warm object to its
> surface area. Small object, such as the patas monkey (body mass of about 5
> kg) cools faster than big object because it has small ratio of heat stored
> in the body to its surface.

Marc Verhaegen wrote:

> Yes, but what is the relevance to sweating IYO? Other mammals wet parts of
> the body to cool (esp.small mammals? eg, rats?) &/or pant (dogs...).

Small animals can cool themselves easily.
Their main problem is to stay warm.
Have you noticed the thin waist of the wasp?
The thin waste prevents loss of precious
heat from the flight muscles to the rear
part of its body (called abdomen). The flight
muscles work only when they are warm.

Big tropical animals easily overheat, so cooling
is their big problem.

Marc Verhaegen wrote:

> What is the salt concentration of horse or patas sweat?

I do not know.
.

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