Re: AAT and the bones
Elaine Morgan (Elaine@desco.demon.co.uk)
Sat, 12 Aug 1995 11:59:07 GMT
Reply to Alex Duncan
I would love to hear your prediction on Ramidus. I'm sorry and puzzled
that you found mine a cop-out. Did you expect something exotic? I don't
know why you should have. I have often argued that if you dug up the
fossil of an extinct mustelid it would be impossible to tell whether
its life-style had been that of an otter or that of a pole-cat.
You say: "the most reasonable explanation of why Lucy had arboreal
adaptations is that she was a partially arboreal creature." Sure. no
problem. I didn't think we were arguing about that The arguments
against it come from the die-hard savannah buffs, not from me. I
thought we were disagreeing about the nature of the substrate which
caused her to stand upright during the time spent at ground level.
The models I have recently quoted most often have been creatures like
the proboscis monkey, the bonobo, Oreopithecus, all arboreal to a large
extent.
On the question of when a hypothesis is a dogma. I am as strongly
predisposed to think AAT must be right as you are predisposed to think
it cannot be right. Not more so, I think. Yes, the AAT scenario has
been modified to fit the facts as more facts emerge. But God knows that
was true in spades of the savannah theory, and is liable to be true of
its successor. What would it take to falsify s/mosaic theory?
Physics is supposed to be a hard science. But it was a physicist
Lichtenburg who said that instead of saying "I have explained such and
such a phenomenon" the scientist should say only: "I have determined
causes for it the absurdity of which cannot be conclusively proved."
You have perfect confidence in your version because you know it passes
that test, and you are right. It does. The most I expect from this
debate is the concession that AAT also passes that test. It is a
genuine contender.
Darwin said that for a false fact to get into the scientific record can
cause immense damage in the time before it is nailed and exposed, but a
false hypothesis can do nothing but good, because it causes people to
re-examine the premises of their own beliefs and tighten them up. AAT-
true or false - could not even perform that salutary service as long as
it was dismissed as a looney fantasy on a par with Chariots of the Gods.
Bipedalism.
You ask what I regard as the non-AAT theories about bipedalism and why
I do not accept them. Here is a list of those that spring to mind. Some
are obsolete, but included for the sake of completeness.
1.The original naive assumption: "stood upright to run faster and better"
Long discarded: everybody now seeks for the non-locomotor advantage.
2 Tools. To carry tools and weapons. We now know b.p. preceded tools
and weapons.
3. To free the hands. It only frees the hands of one sex. It enslaves
the hands of females with young which can no longer ride on their backs.
4.Sentinel theory; to look out for predators. Dozens of totally
unrelated species use this strategy. In every case having spotted the
predator they run away on four legs because it is faster.
5. Endurance running. A biped can run down a gazelle after the first
ten or twenty miles. Teleological. No ape would practice shambling the
first twenty yards in the faith that its distant descendants would
be good at the marathon.
6. Pair bonding. Because our young develop so slowly, a male input
in child-rearing was necessary. Males stood upright to carry food
home. What food? An ape would transport a small dead animal by
running on 3 legs and dragging it. Carrying back handsful of seeds
would be absurdly energy-expensive. While the males were off
foraging females and young would be undefended. Anyway we now know
when b.p. emerged, the young developed as rapidly as the young of a
chimpanzee. The pair-bonding is pure speculation.
7. Gelada model . To save time moving from one patch of grass to
another, geladas do not locomote on 4 legs so their hands can be busy
all the time. They don't locomote on two legs either; they shuffle
along on their bottoms.
8. Thermoregulation. Standing up minimises intake of solar radiation
by exposing a smaller area of body surface to direct rays of sun at
midday and for an hour or two eah ide of noon. But we now agree these
creatures were partly arboreal. They were not mad dogs or Englishmen:
they would have siesta'd in the shade. Wheeler himself, main proponent
of thermo theory, in later papers discusses how long a siesta was
obligatory to preserve water-balance.
9. Gathering. This is Hunt's contribution - he established that chimps
in wooded country stand on two legs to reach up and feed - whereas
they don't stand or walk upright at all in the Savanna sectors of
s/mosaic which most theorists concentrate on as the trigger of b.p.
I loved Hunt's paper. But I think the transition from postural (and
often branch-holding) b.p. to locomotor bipedalism is more difficult
and unlikely than he allows for. Even some ungulates (gerunuk) stand on
two legs to feed.
10. Provisioning for journey. The protohominids stood up to carry food
and water across the increasingly wide open stretches between one patch
of forest and the next. They'd have needed much forsight to know how
long the journey would take, and great self-restraint not to drink as
soon as they got thirsty. Anyway we can observe chimps in s/mosaic
conditions where the wooded sector is down to 5% of the territory. That
is not how they behave.
11. Avoidance of mayhem. Apes stand (and briefly run) erect to show
willingness to fight and thus avoid actual conflict. Scarcer resources
in open spaces meant more risk of conflict , hence intensification of
this behaviour. But primate peace-making demands also submission
behaviour from some - in fact from the majority - of a primate band,
notably the females. Everybody signalling readiness to fight all the
time would be pretty disastrous.
Soft tissue changes. Yes, I was too glib is speculating why they might
happen faster than skeletal ones, and deserved the polar bear crack.
You ask what is my evidence for supposing that nakedness, sweatiness,
and polydipsia were acquired pre-afarensis. No evidence either way, but
it would be strange and perverse if they emerged after 2.5mybp. It
would necessitate frequent attendance at water-holes and they are
dangerous places.
On whether the taxonomic bush of bipedalism had more than one root, you
merely comment that it must have been a pretty extensive inland sea.
Well yes, it was extensive. But this wasn't actually an AAT question.
It is just as valid without any water at all. There must have been
groups of prehominids isolated from one another in wooded areas by arid
open stretches too wide to cross. If you really believe bipedalism was
a predictable response by one particular species to those conditions,
why could it not have happened more than once? I just wanted to know
how far we are wedded to the concept that it only happened once.
You say the non-skeletal changes I listed - naked skin, fat layer.
disturbance of sodium homeostasis, descent of larynx, loss of
estrus, etc. - "have all been adequately explained by less far-out
hypotheses".
That has not been my impression. If you can give me five references,
one for each of these characters, offering explanations that you
personally find convincing, I will be astounded.
Elaine.
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