Re: Sweating hominids

Marc Verhaegen wrote:

> c) SC fat layers in mammals are only seen in animals that come frequently in
> contact with wet soil or water.

This is another hint that heat loss in water is
a serious problem for warm-blooded animals.
Aquatic birds rub hydrophobic (repelling water) oil
into their feathers to improve thermal insulation
of their feathers. A petroleum (oil) spill is a
disaster for them because the petroleum dissolves
their hydrophobic oil and destroys their thermal
insulation.

Andrew Nowicki wrote:

> 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.)

Marc Verhaegen wrote:

> What does all this mean in the case of patas & horses IYO?

Long hair generally insulates better than short hair.
Patas have long hair, which indicates that heat loss
is a bigger problem for them than overheating. I am
surprised that they sweat through their long fur --
it makes as much sense as an overheating, sweating human
dressed in a fur coat.

Horses are big animals covered with short fur. Big
animals generally have too much heat rather than too
little heat. Short fur seems to be just right fur
length for the horses because it does not substantially
impede cooling due to sweating, and it provides some
protection against biting insects.

Andrew Nowicki wrote:

> 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.

Marc Verhaegen wrote:

> ?? Andrew, have you any evidence for this?
> Humans have 3 sorts of hair follicles: terminal follicles (clearly visible
> hairs, eg, scalp, beard, pubis, axilla...), vellus follicles (the nearly
> invisible hairs on our naked skin), and sebaceous follicles (which cause
> acne in face...). I never heard that mosquitos preferrably used these
> places, nor that our skin is easier to be pierced there?

A friend of mine told me about this.
I have seen the mosquitos probing my skin
before biting, so I believed he was right.
I could not find anything on the Internet
confirming this info. Here is what I found:
- http://scienceweek.com/2004/sb040416-6.htm:
"Once through the skin, the mosquito's proboscis
begins probing for a tiny blood vessel. If it
does not strike one on the first try, the mosquito
will pull back slightly and try again at another
angle through the same hole in the skin."
- http://www.myccr.com/SectionTechnique/Problems/Mosquito.htm:
"How many mosquitoes do we have in Canada?
Nobody knows, but a ballpark estimate of the US
population is 10 trillion, and that's a small number
compared to our prolific Canadian population. It
has been estimated that the combined weight of
mosquitoes in the Northwest Territories would
exceed the combined weight of all of the caribou
herds - a sobering thought."
Well... This is not the whole story. Mosquitoes do probe
my skin before biting. Sometimes a mosquito walks on my
skin for a few seconds before finding the right place to bite.
You can solve this mystery with the help of one hungry female
mosquito and a magnifying glass (or a Nikon Coolpix camera --
they make best macro photos).

Marc Verhaegen wrote:

> Lower limit in semi-aquatics in tropics = humans & babirusa (some rivier
> dolphins = fully aquatic are even smaller).

Humans and babirusa are not aquatic animals.
Babirusa look like pigs. To the best of my
knowledge their only aquatic behavior is
wallowing in mud.

The smallest dolphin species is La Plata
(Pontoporia blainvillei), weight: 30-53 kg.
(source: http://www.wcug.wwu.edu/~narf/dolp/riverd.shtml)

If any hominids were aquatic, they were early hominids,
either apiths or their ancestors. These early hominids
were smaller than humans. For example, the weight of
Australopithecus afarensis is similar to the weight of
the smallest (La Plata) dolphin. A truly aquatic, hairless,
warm-blooded animal has at least 3/4" of subcutaneous blubber.
Imagine a small, tropical hominid having such a thick layer
of blubber. Hominid body shape is much less streamlined than
dolphin body shape, so at least half of its body weight
would be blubber. Such a blubbery hominid would be clumsy
on land and it would quickly overheat (hyperthermia) in
the hot tropical afternoon.

Andrew Nowicki wrote:

> This suggest that heat loss for human-size aquatic animal is too high.

Marc Verhaegen wrote:

> Not in the tropics, see above.
> The neutral Tp for humans of recreational swimming in tropical waters is
> 25-28°C (dependent on water currents etc.), ie, the normal Tp of tropical
> waters, this means that without scabu equipment etc. you can stay
> comfortably in the water for hours.

Please read my first post in a new thread
titled "Final Solution of the Aquatic Question."

Andrew Nowicki wrote:

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

Marc Verhaegen wrote:

> Yes, that why it's not very sensible to think that humans (with SC fat about
> 10 times thicker than chimps) once lived in savannas or so.

Subcutaneous fat makes you feel really hot when
you walk in the hot, summer day. However, it is
hard to say how much subcutaneous fat the early
hominids had. The hairless ones surely had some
fat to keep them warm at night.
.

Relevant Pages

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  • Re: Sweating hominids
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    (sci.anthropology.paleo)
  • Re: Sweating hominids
    ... >> c) SC fat layers in mammals are only seen in animals that come frequently ... >> in contact with wet soil or water. ... If the fur is much longer that about 1 mm, ... >>> Note that female mosquito probes your skin before she plunges her ...
    (sci.anthropology.paleo)
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