Re: Why is Homo sapiens hairless?
Rohinton Collins (rohinton@collins.prestel.co.uk)
5 Nov 1996 22:06:39 GMT
JW> Human females have a fixed layer of subcutanous fat
JW> concentrated in certain parts of their body.
Firstly John, in response to your original statement, human females do not
have a fixed layer of subcutaneous fat concentrated in certain parts of
their body. They have a fixed subcutaneous layer all over their body (as do
men), but most women have extra 'padding' on the buttocks, hip, thigh and
breasts.
RC> Exactly, only certain parts. This is for storage, not
RC> insulation (although it doubles up on this score).
JW> How do you know what it's for Roh? If it is for
JW> storage, why is it only found on the female? And why don't Ape
JW> females have similar stores of fat?
A lean (slim) male or female human will have no extra padding, just a
continuous even layer of subcutaneous fat. This is not commonly the case,
although, I myself have no additional fat deposits - technically called an
ectomorph. If more weight (fat) is put on, the fat will not be laid down
evenly. Although extra fat will be laid down all over the body, additional
deposits will be made: in the female - as detailed above; and in the male -
on the belly. Or have you never seen a beer-belly? Now, I said this fat was
for storage because as well an insulating the body, fat is the body's
primary energy resource. These deposits are not intended (by nature) to
insulate further, indeed they are only a result of our modern lifestyle -
overindulgence. As to why apes aren't fat: they obviously don't overeat,
and underexercise, which is what we are guilty of.
JW> This is a permanent form of insulation which means they require
JW> less body hair than primates without such layers of fat.
It is anything but permanent. Are we talking about the same fat deposits?
The ones that most women seem to be dieting to get rid of?
RC> This is too simplistic. You are equating the present
RC> human condition (who
RC> mostly wear clothes, by the way) with that of the first
RC> hairless hominid.
JW> No, Roh. I'm equating the present human condition with
JW> all primates,
JW> period. No other primate has such a permanent form of
JW> insulation. If they did,
JW> it is my contention that they wouldn't need so much body
JW> hair.
Is not fur a permanent form of insulation? It seems to work for the
majority of mammals. You are mistaking cause for effect. Or perhaps there
is no cause and effect viz a viz subcutaneous fat and hair-loss. I don't
believe that we became hairless because of an increase in subcutaneous fat,
which is your theory. What is more likely, is that subcutaneous fat
necessarily increased AS body hair decreased DUE to a third factor. After
all, why haven't other mammals, for whatever reason, not followed our lead
and lost their fur with a concomitant increase in subcutaneous fat? Because
no other mammal wears clothes. This, I believe, is the third factor.
JW> If clothes were used as a means of camouflage, and the
JW> maintenance of the camouflage was essential for survival,
JW> then there would be an advantage accruing to hominid
JW> individuals with less hair, or more sweat glands etc.
RC> Again, camouflage in this instance would also have been a
RC> secondary consideration. Surely clothes would first have been used
RC> for insulation and protection, and then for camouflage?
JW> You are a difficult person to please, Roh. I have gone
JW> to great trouble here to make a case for your clothes theory. I have
JW> avoided the insulation question for obvious reasons. Insulation against
JW> what? The heat? The cold?
Both.
JW> Not the heat, for reasons you have stated.
??? Please explain. Clothes would shield the body from solar radiation. And
as long as they weren't too tight would not hinder the sweating process too
much.
JW> What about the
JW> cold? Consider your theory. The species are hairy, but they still
JW> feel cold. So they invent clothes and start wearing them. Right?
JW> This enables them to exist in colder, or more exposed habitats.
JW> But why would this lead to less body hair, since this would reduce
JW> their insulation? And more sweat glands would make them colder
JW> still. It wouldn't make sense, would it?
It is a question of balance. If the climate is likely to be hot only, or
hot and cold, either daily or seasonally, or both, then a naked, clothes
wearing, sweaty ( ;-) ) hominid would fare better than a hairy hominid.
In the heat the hairy hominid would be uncomfortable. It would be shielded
somewhat from the solar radiation, but would soon overheat in the mid-day
sun and so would have had to seek shelter at noon. The naked, clothes
wearing hominid could venture out in the mid-day sun. Its clothes would
shield it from direct solar radiation, and it would not overheat since heat
could be lost due to sweating.
In the cold both hominids would fare quite well. But in the extreme cold,
only the clothes wearing hominid, who could pile on the furs, and cover the
feet, would prosper, or indeed even survive.
I hope my ideas are now clearer to you John.
Regards,
Roh
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