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More Morgan/Nicholls
Phil Nicholls (pn8886@csc.albany.edu)
18 Jan 1995 16:51:20 GMT
In article <41277856wnr@desco.demon.co.uk>
Elaine Morgan ( usenet@demon.co.uk) writes:
> Here's the bit you're waiting for. What Sheila
> Mahoney did not specify in 1980 has now been specified
> in spades. By 1980 Elizondo really got his act together
> and I am not going to argue with him: patas use eccrine sweat-
> cooling. This means (a) I have to accept that the latent
> capacity in Old World monkeys to find a new use for their
> non-volar eccrines can be activated in a terrestrial
> habitat and (b) you have to accept that ST's front-
> running explanation of human nakedness ("a necessary
> accompaniment of sweat-cooling") has gone down the tubes.
> The patas is a notably hairy sweat-cooling savanna-
> dweller. Why isn't it as naked as we are if it was
> responding to the same conditions?
Patas monkeys, like baboons, are rather inactive at mid-day,
foraging mostly in the mornings and late afternoons. Wheeler's
scenerio calls for a sustained exploitation of patchy savanna
resources. I would like to see data on the rate of heat loss
by convection before I buy into it. Personally, I don't see
any reason to assume australopithecines had any less body hair
than what is usually found in primates today.
Again, I see more of a connection between increased
thermoregulatory capacity and brain size. Hair loss many not
have occurred until the genus Homo itself shows up, about 2.5
million years ago. At this time we have definite evidence
that hominids were savanging on the savanna.
> I don't think you can sustain your theory that
> humans switched to eccrine sweat because it was more fine-
> tuned. There is considerable delay before it responds to
> a rise in temperature. One estimate (Ingram & Mount,1975)
> gives between 4 and 40 minutes. There is equally hazardous
> delay in switching it off when the sweat is dripping into
> the sand serving no purpose and causing dehydration and
> heat cramps. Reactions of apocrines in anthropoids
> are I agree spasmodic in operation (their function there
> is pheromonal) but where, as in cattle, they have been
> adapted for thermoregulation they work very smoothly.
You are making an optimal design argument which doesn't really
work in reconstructing evolution. My suggestion of finer
control is derived from the neurophysiology. Systems that are
cholinergic (use acetylcholine as a neurotransmitter) are
systems that require a greater degree of regulation.
Eccrines, as I stated before, are innervated by cholinergic
neurons while apocrines are innervated by adrenigenic neurons.
Therefore, while it may not seem like fine turning if you are
going for optimal design, evolution must use structures
already present. Selection favored eccrine glands because
there is greater control over ther output.
I also pointed out that increased brain size places a greater
burden on thermoregulation systems which would in turn explain
why apes have more eccrine glands than monkeys and humans have
more than apes.
> You would now like to say: Right. Patas have eccrines. Story
> over, AAT demolished, QED. It is not that simple. Your
> constant theme is that the differences between apes and men
> need no explanation but are merely a continuation of trends
> already discernible in the differences between monkeys and
> apes. This contention is simply untrue.
No, that is not what I am saying. I am saying that your claim
that many of the characteristics you claim as anomalous are in
fact understandable within the context of general evolutionary
trends in primates. These include bipedalism, eccrine
sweating, nose shape, reduction in size and number of apocrine
glands, the descended larynx and these are only the ones I
have had time to look at.
I will take you list of "non-trends" for future study when
time is available. Right now I must pick up other obligations
associated with my graduate program. If I had not already
committed myself to a dissertation topic I might give serious
consideration to looking at sweating and thermoregulation
issues. I will set them aside for post-dissertation research.
I would like you to consider the following.
The one characteristic you don't discuss much is brain size.
Cetaceans and hominids are both very encephalized but you
can't make the argument for convergence because we know that
brain size in hominids doesn't take off until Homo habilis.
Consider that without this fossil evidence it would very
likely be in your list.
In addition to increased brain size we see a reduction in
alveolar prognathism and a reduction in the size of the
posterior dentition. What if Australopithecines were hairy.
What if body hair changes are associated with increased
thermogulatory demands associated with increased brain size?
--
Philip "Chris" Nicholls Department of Anthropology
Institute for Hydrohominoid Studies SUNY Albany
University of Ediacara pn8886@cnsunix.albany.edu
"Semper Alouatta"
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