Re: Bipedalism and theorizing... was Re: Morgan and creationists

Paul Crowley (
Thu, 18 Jul 96 14:08:49 GMT

In article <> "Gerrit Hanenburg" writes:

> The point is that ape infants can cling to their mothers in orthograde
> positions,whether in the trees or on the ground.

Apes at rest commonly adopt an orthograde sitting position and,
as you suggest, their infants have no difficulty in clinging on.
Similarly when feeding in trees an othograde position is normal;
but then the mother's movements are slow and careful and the
infant's safety is regularly checked; think how a modern h.s.s.
mother would manage with an infant when climbing trees! OK, an
early bipedal hominid might find it easier, but not much easier.

> You haven't pointed out why it is impossible
> (anatomically/biomechanically) in bipedalism,which is just another
> form of orthograde positional behavior.Your diagram didn't show
> that,it only showed different postures.

Walking or running with infant attached is a very different matter
from just sitting with one. It's absurd to say it's "just another
form of orthograde positional behaviour". You should be able to
see its near impossibility from my ascii drawing; to go beyond that
I'd need an animated cartoon.

> Neither have you made it clear why it easier to hang on underneath the
> mother with nothing to support the infant.

I shouldn't need to. It's basic physics/engineering. You can
hold onto a horizontal branch of a tree, wrapping your legs and
arms around it -- even if it moves around; but you can't hold
onto the vertical trunk of a tree unless you have good foot- and
hand-holds; and if the vertical trunk starts moving along,
bouncing up and down, you've got no chance of staying on.

Ape infants, when they're born, have arms and legs that are long
enough to reach the mother's sides and have grasping hands and
feet that are strong enough to hold and bear its weight. It's a
design that goes a very long way back in primate evolution, maybe
over 100 Myr. It was probably *the* distinctive primate
adaptation. (Is there a primatologist in the house?) It required
singleton births and suggests a nomadic arboreal existence.

The abandonment of this basic primate behaviour was undoubtedly
*the* distinctive hominid achievement. I'm sure it occurred prior
to bipedalism, and was a necessary condition for it. It wasn't
something that just "faded away" at some uncertain time and for
some uncertain reason -- as standard PA would have it. Whenever
it happenned, it was a major behavioural shift. Standard PA
suggests it was caused by brain growth. But the costs of such
a shift would have been great and would have exceeded whatever
benefits might have accrued from a small increment in brain size.
So standard PA must assert that there was a sudden increase in
brain size and a whole new way of hominid life. -- None of it
makes any sense. The inability of standard PA to face up to this
problem, to give a precise account for this shift and to state
detailed reasons for its occurrence, is a mark of its overall,
abject failure.

> Just because chimps seem the only alternative living model doesn't
> mean it's an appropriate model.We simply do not have a living model of
> a bipedal,small-brained,hairy ape and thus there's nothing to compare
> the chimps with.This doesn't render infant carrying in such a
> hypothetical ape impossible.

We have an excellent living model for a bipedal ape. Its brainsize
may be bigger than we'd like, but that has little relevance to its
locomotory behaviour. Its infant carrying behaviour is likely to
be much closer to that of early bipedal hominids than that of a
quadrupedal chimp.

And why should early hominids have been hairy? The parsimonious
and normal assumption is that all the distinctive features of a
species were adopted at the point of speciation. Fossil or other
data may modify this assumption, but we have no reason to modify
it in respect of hair.

> >The link between brainsize and secondary altriciality is an
> >assumption, made without evidence. It's a hang-over from the
> >days of "brains before bipedalism". It made good sense -- then!
> It still makes sense today.

On reflection, I don't think it made any sense at any time.

> The pattern of postnatal braingrowth is
> part of a pattern of delayed development in modern humans which causes
> secondary altriciality.

The cause of secondary altriciality in infant hominids is their
inability to learn normal locomotory behaviour within a reasonable
period. They can't stand for the first year and competent loco-
motion is not generally acquired until the third year. This is an
extraordinary state of affairs which applies to no other species.
Without normal locomotion, an infant is necessarily altricial; it
can't fetch its food; it has to be carried everywhere (or be put
down). No one has ever suggested that early hominid infants
would be any different. If anything, they'd be worse. It's got
nothing to do with brain size and everything to do with bipedalism.
Imagine what it is like to have both legs amputated. You'd be
just as "altricial" (i.e helpless).

> Since Australopithecines had brains not much
> bigger than chimps it's not likely they had the pattern of postnatal
> braingrowth of humans,but a pattern similar to chimps.We may therefore
> assume that they had precocial infants that could cling to their
> mothers shotly after birth.

This is appalling logic. I know it's standard. That makes it even
more appalling.