Re: Sweating hominids

"Andrew Nowicki" <andrew@xxxxxxxxxx> wrote in message
news:42E36391.C756DE32@xxxxxxxxxxxxx

>> 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.

Yes.

>>>AN: 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.)

>> 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.

Yes, I'm surprised too (overheated sealions sweat on the naked flippers to
cool, not under their fur AFAIK), but some papers suggest that patas have
thermoactive sweating almost as strong as humans. Ask the dry apers.

> 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.

Possible. It probably also protects against averheating by reflecting sun
radation. Shaved sheep overheat more readily.

>>> 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.

>> ?? 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).

IOW, you don't have any evidence that mosquitos plunge their proboscis into
follicles. Very unlikely IMO. Perhaps you confuse "follicle" with the
"cavity" their anti-coagulans creates? My own impression is that they
perhaps have a slight preference for superficial veins.


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

> Humans and babirusa are not aquatic animals.

Nobody said that. What is your point?

> Babirusa look like pigs. To the best of my knowledge their only aquatic
> behavior is wallowing in mud.

They live on islands (Celebes, Molukka), swim to coastal islands: "...has
habits much like other Suidae, though it is one of the most aquatic,
freqenting marshy forests."

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

Yes, that's what I said.

> 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.

Yes, confirms our view.

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

>> 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."

OK.

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

>> 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.

Yes, difficult to know, but it's unlikely that apiths, at least the gracile
ones, had much fat: they had climbing (suspensory) features. AFAIK arboreal
mammals are not fat (except small arboreals during torpor locally: fat
tails) - too heavy I guess.

> The hairless ones surely had some fat to keep them warm at night.

Common mistake. If they had to keep warm at night, they had kept their fur.
Fur & fat have nothing to do with each other: they have very different
functions: some mammals are fat+furred (most pinnipeds, mammoths...), most
are lean+furred (>9/10 of mammals), some are lean+furless (elephant,
aardvark...), some are fat+furless (Cetacea...).

--Marc



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