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

Gerrit Hanenburg (
Wed, 17 Jul 1996 18:13:17 GMT

Paul Crowley <> wrote:

>We need to focus on the predominant locomotory behaviour; for
>chimps and early hominids that's on the ground. Since orangs and
>gibbons hardly ever come to the ground, their locomotory behaviour
>is largely irrelevant. In any case, the predominant locomotory
>behaviour for female orangs appears to be a slow movement through
>the canopy; and that of gibbons is brachiation with raised hind
>limbs which help to prevent infants falling off.

The point is that ape infants can cling to their mothers in orthograde
positions,whether in the trees or on the ground.
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.
Neither have you made it clear why it easier to hang on underneath the
mother with nothing to support the infant.

>Chimps are the only appropriate alternative model. They need
>rapid and effective terrestrial locomotion (like early hominids?);
>they achieve it with their trunks in a horizontal position.

Knuckle-walking is a compromise between living in the trees and moving
on the ground and as such it is not a very rapid or effective way of
moving on the ground.It does get you from one place to another but to
a considerable cost,and in the case of danger chimps rely mostly on
their climbing abilities to get them to safety.
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.

>> given their small brainsize,didn't yet have secondarily altricial
>> infants.

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