Re: Bipedalism and endurance (Re: AAH - enough already)

Bryce Harrington (
14 Dec 1994 18:12:17 -0800 (Gerold Firl) writes:
>Pat Dooley <> writes:
>>loopy <> writes:
>>>............................................ you want your skin to be
>>>cool, not your hairs. Naked skin on the other hand allows for the most
>>>efficient cooling of the _skin_.
>Taking it from the top: other savanna creatures have not exploited the
>evaporation-based high-heat-rejection path because they have not occupied
>the high-temperature-activity niche. Only humans have done so. This is not

How do we know that humans are adapted to high-activity-hot-weather
niches? I think this is an assumption made by the Sweaty Ape
Hypothesis and using it as proof is just so much circular logic.

>Loopy is quite correct about the relative merits of naked vs. furry skin
>when trying to cool the body underneath. Fur will wick sweat away from the
>skin, where heat provided by the flow of the surrounding air will
>evaporate it. This is nearly as bad as sweat which drips off the body, to
>evaporate on the ground. It doesn't help the animal to cool. The sweat must
>be in thermal contact with the skin as it evaporates, or else it is

Not true. Fluid evaporating off of a surface will directly result in
good heat loss, but fluid evaporating off of a surface near the skin
will also give some heat loss. Think about it this way. When you
step out of the shower, the water on your body evaporates quickly
and makes you colder than the water on your head, but after 10 minutes,
the water in your hair is still there (for the most part) and still
keeping you (relatively) cooler than the remainder of your body.
Plus, the water in your hair is remains longer and helps cool better
than the rest of your body. Also, evaporation does not care about
water quantity as much as about surface area, so when you compare
water evaporating off skin with water evaporating off skin+hair,
you can see that one will give better results than the other.
When I run, the sweat in my hair gives me better cooling than the
sweat on my chest.

And that's not all the story, either. You also have heat reflection/
absorbsion going on. As the AAH people have constantly pointed out,
the presence of hair will serve to reflect more heat than bare skin.
This alone could help a great deal in an environment proposed by
the SAH.

So I conclude from all this that no simple arguments can be made about
sweating that demonstrate the superiority of the human cooling
system. The above is just a intuitive feel for the subject, but I'm
pretty sure about it. I'll pull out my Thermodynamics book and do
the math one of these days just to be sure, but I'm fairly certain
of the rough feel already.

>>You might also observe that people living inhot, arid regions,
>>wear long, flowing clothes. It keeps them cooler than going around
>>in loin clothes and relying on their skin alone to cool them
>You'll also notice that when people run marathons under hot conditions they
>wear as little as possible.

I would propose that under severe heat, as suggested by the SAH,
wearing better clothing would result in more efficient cooling, or at
least less water loss. I would also put forth that running marathons
is not something that our ancestors would have been doing enough to
make an impact on our evolution.

>The whole human skin/sweat system is obviously a
>specialised adaptation for high temperature activity, which makes a serious
>inquiry into a hypothetical aquatic phase in our evolutionary history look
>like a total waste of time.

First, even if the human body *was* adapted for high temperature activity,
I don't see how this disproves AAH. It is entirely possible that these
things happened *after* the AAH adaptations. AAH has shown at least one
way in which these traits _could_ have evolved, a way which is just as
plausible or implausible as the SAH.

Second, the SAH doesn't explain *why* this kind of adaptation was
required. The only thing I've seen is that it helps when chasing down
horses and so forth. Yet the literature is pretty clear that the idea
of proto-humans as carnivores has pretty much been disproven. So
what were we adapting towards? Running *away* from predators requires
speed, not stamina. Covering great distances? This can easily be done
at cool times rather than at hot times of the day.

In my Explorer Scout survival training I remember hearing that a man
could die (yes, DIE) in about half an hour if he walked in the desert
sun at midday without any water. Doesn't sound like high temperature
adaptation, to me folks. 'Course, that was in the desert, but the
savannah is pretty close to the same thing.

>There are plenty of interesting questions
>regarding our evolution which we don't understand. why waste time on this,
>which we do?

You know, whenever I hear this (non-)argument it makes me smile. You're
saying, "I just want us all to forget about this theory because it goes
against everything I know." My opinion is, maybe it IS false, but why
not give it a fair shake? If it was *really* as pseudo-scientific as
you think it is, I don't think so many people would support it. I know
*I* wouldn't, but I'd still keep an open mind about it.

Another reason I smile is because this theory, if nothing else, has
brought up a number of human features which are typically ignored
by paleoanthropologists: the nose, adiapose fat, the sweating
system, etc. Are these things also a waste of time? They are
certainly areas we do not quite understand. In fact, the nose is
such a problem to non-AAH people that the most solid alternative
argument I've heard about it is, "Well, not everything needs to
be explained."