Re: ALEX's References
Alex Duncan (email@example.com)
22 Aug 1995 19:29:24 GMT
Elaine Morgan <Elaine@desco.demon.co.uk> wrote:
>I did not question that there is abundant literature.What I was looking
>for was "Less far-out hypotheses" (didn't get them) and "explanations
>that you personally find convincing". Your first comments on the
>Laitmann and Lieberman papers were that some of their conclusions are
>highly controversial and that you personally think their
>reconstructions are erroneous.
>More basically,they do not even set out to address my question of why
>the larynx descended. They discuss the date of this event and its
>consequences, but not the reason for it. They try to establish the
>date by attempting to relate the descended larynx with the shape of the
>basicranium of fossilised skulls. They are handicapped by the fact that
>the only extant example they educe of an animal with a descended larynx
>is Homo sap., and it is always risky generalising from a sample of one.
My main point in citing those references is that they demonstrate a
possible correlation between a descended larynx and basicranial flexion.
I think Laitman & Lieberman's conclusion re:Neandertals are controversial
because they have not adequately demonstrated that Neandertals did not
have basicranial flexion that approximates that of modern humans. There
is, however, abundant and non-controversial evidence that the basicrania
of gracile australopithecines and earliest Homo are not nearly as flexed
as those of modern humans. If the descended larynx is indeed associated
with basicranial flexion, then this demonstrates that the descended
larynx is a relatively recent acquisition in hominids. Since you
postulate that it evolved in an aquatic environment, then we are left
with the conclusion that the earliest hominids must not have been
aquatic, but that early moderns were.
>Your list on nakedness consists in effect of Wheeler and his
>commentators, and you find Wheeler's model convincing, so let's talk
>about it. Wheeler's thermoregulatory model of bipedalism addressed the
>question we should all ask: Why are we so different? What was unique
>about our ancestors that it made it expedient for them alone to walk on
>His answer depended on the then classic Dartist theory that the
>hominids were unique in that they were the apes who went out onto the
>savannah. Erect posture kept them cooler because in the middle of the
>day they exposed a smaller percentage of body surface to the direct
>rays of the sun. The noonday sun falls all along the back of a zebra,
>but only on the top of a man's head. QED.
>Wheeler has now updated his backdrop from the savannah scenario to
>"relatively open equatorial environments". He admits the possibility of
>available tree cover nearby, and envisages the hominids taking a siesta
>in the shade, as I years ago suggested they would do. He says,
>"Although others have postulated a specialist meridian niche for early
>hominids, I have not....My own views are that there would have been no
>particular premium attached to the period around noon, and that
>hominids would not have exposed themselves to unnecessary heat stress."
>But he still thinks that bipedalism would have enabled them to extend
>their foraging hours into the period around noon on occasions when it
>became necessary, and that this alone would provide enough natural
>selection pressure to account for b.p.
>The point is that whether or not there was a premium attached to
>foraging at noon, the period around noon is the only time at which
>an erect posture minimises the intake of direct solar radiation.
>At six in the morning or six in the evening the sun's rays will hit a
>solid object at an angle on the equator of 45% whether it is a
>verticAL object or a horizontal one. If the primates with their large
>brains occasionally needed to extend the diurnal duraion of their
>foraging, it would have been possible to extend it by starting earlier
>in the morning and finishing later at night. That would have been one
>hell of a lot simpler than insisting on extending it into the period
>around noon, and for this sole purpose revolutionising their entire
>life style and body plan, learning to shamble along on two legs,
>redesigning their skeletons
> and muscles and circulation and forcing
>their females to carry their young in their arms everwhere they went.
You apparently have either not read Wheeler, or misread. You are correct
that heat intake via solar radiation would only be reduced in the period
immediately around noon. However, solar radiation is not the only source
for heat uptake. Air temperature is also important, and Wheeler has
demonstrated that a biped has a higher rate of convective heat loss (not
evaporative) than a quadruped, simply because so much surface area is
maintained at a higher level above the ground. There is a steep
temperature gradient from the ground to a level several meters off the
ground (temps. on the ground may be as much as 20 deg. C higher than
those at a level a meter or so above the ground).
>All the rest of the Wheeler hypothesis rests on this extremely rickety
>basis. |Now that the hominids are vertical, as long as they keep a
>thatch of hair on their heads they can dispense with all the rest of
>their hair to facilitate cooling. No other land animal has been smart
>enough to think of this.
No other land mammal is bipedal, is it?
>They could all have a covering of hair along
>their backs and let their flanks go naked since they are perpendicular
>and not exposed to the direct rays of the tropical sun. In one debate I
>reminded Peter that if you shave a portion of hair from the back of an
>animal in the tropics its core temperature goes up, not down. He
>laughed and said that remark was predictable. It was the only time I
>have heard Predictable used as a synonym for irrelevant, As I have said
>before, he is a very nice guy. I just don't think he's got the answer.
What is the question to which you don't think he has the answer? If the
question is "are sweating and naked skin adaptive for a diurnal, bipedal
primate living in the tropics in a mosaic environment?" then he does have
the answer, and it is unequivocally "YES."
We should expect that if shave the hair from the back of an animal in the
tropics its temperature would go up. After all, especially around
noontime, the back is the portion of the animal that will have the
greatest exposure to solar radiation. The analogous surface in humans is
the top of the head, which is covered in hair.
>Alex says: "loss of most of the body hair will prove to be adaptive,
>provided you're sweaty enough". Well, he should consult here with Phil
>Nicholls who will tell him how copiously our friend the patas monkey
>sweats, and how effectivly, and yet its coat is thick and deep and
>lustrous, even on the flanks where it would be so expendable. Why
>do you think that is?
I should have said "loss of most of the body hair will prove to be
adaptive, provided you're sweaty enough, and bipedal."
>It is all a circular argument. We became naked because we were sweaty.
>We became sweaty because unlike the chimp we were naked so our sweat
>would be effective. We became naked and sweaty because we became
>perpendicular. We became perpendicular and sweaty and naked because
>our ancestors were unwilling to get up earlier in the morning.
You seem to misunderstand the argument. You asked whether or not there
was some plausible explanation why hominids are hairless and sweaty. To
my mind, plausible means "demonstrable adaptive advantage." The
demonstrable adaptive advantage in this case is that being sweaty and
hairless keeps a biped cooler. Do you deny this statement? If not, then
I suggest it is very plausible.
You really seem to have some basic misunderstanding of what Wheeler has
demonstrated: that sweating is an efficient cooling mechanism for a naked
bipedal animal. You asked what possible plausible explanation there was
for sweating, and I have provided one. I might add that while it has
been demonstrated that sweating helps keep a naked biped cool, it has not
been demonstrated that sweating will help an aquatic animal maintain an
appropriate sodium balance.
Dept. of Anthropology
University of Texas at Austin
Austin, TX 78712-1086