ALEX's References

Elaine Morgan (
Sun, 20 Aug 1995 17:08:17 GMT

Thank you very much for the Dean and Keleman refs. I will certainly get
hold of them. I am familiar with the rest of the material. Most of it
is in my files and I have quoted from it in books and papers. I have
been focussing my attention on these questions while you have been
consolidating your expertise on the fossil bones

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.

As with bipedalism, an additional snag is that there are no
intermediate specimens. It is hard to imagine an animal which
habitually practices semi-erect bipedalism, as several experts have
pointed out. It is even harder to imagine an animal that would go
through life with a semi-descended larynx. The only creature we know
with a semi-descended larynx is a young baby when in transition from
the normal primate mode to the adult human mode. It is in this
perilous period that it is susceptible to SIDS (cot death)

They debate how the decended larynx, onc acquired, relates to the
evolution of speech. Interesting stuff, but gets us no nearer to why
in this as in so many respects we differ so radically from our
nearest kin. As you say, you are not suggesting this change evolved
as an adaptation for com[plex verbalisation. Neither are they.

What you and they are content to imply is that it "may have been" the
result of a more erect posture. We know this is not true on a
phenotypic level. A child's larynx will descend whether or not it
learns to sit or stand erect. Also it is not true on a species level.
We are talking here about the erectness of the torso. As far as I
know no-one tries to relate laryngeal descent to what is happening to
the legs. There are South American monkeys in which the foramen magnum
is in virtually the same place as our own, because when they sit up
straight they hold their heads in the same relation to the torso.
They do not have a descended larynx.

There is no reason why they should, As Sir Arthur Keith pointed out,
if it was on balance advantageous for the epiglottis to be in contact
with the palate , as it is in all other land mammals,, the trachea
would have gradually increased in length as the basicranial angle
changed. Homo is the only primate species in which this failed to
happen. (AAT suggests the balance of advantage was changed by the need
to inhale large amounts of air rapidly before a dive. The only other
mammals with d.l. are marine ones)

The idea of an exaptive consequence of head posture was a long shot,
and a good try, but it does not accommodate the facts. If reading Dean
or Keleman modifies my judgement on this I will get back to you.

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
two legs?

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.

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. 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.

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?

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.

This is the phantasmagoria you describe as so plausible that no one
worth speaking of has bothered with other models.

I am, as I promised, astounded.