Re: An alternative to ST and AAT

Paul Crowley (
Sun, 10 Nov 96 18:36:31 GMT

In article <> "Gerrit Hanenburg" writes:

> (Paul Crowley) wrote:
> >This raises a very interesting point. For some 2.5 million years
> >(until about 2.5 mya) hominids could not stride and probably could
> >not run; if they could, they certainly did not do it well. The
> >australopithecines had short legs, long arms and no waist.
> Australopithecines,as represented by "Lucy" (AL 288-1),did not have
> long arms. The "intermediate" humerofemoral index (85) is the result
> of a relatively short hindlimb.

This is not true. The male A. afarensis humerus was about the
same length as in both H.s.s. and chimps. The difference in
arm length comes from the ulna; and the male A.afarensis ulna is
almost the length of the male chimp's -- much longer than in H.s.s.
The humero-femoral index is further misleading in that it ignores
body size. Australo total leg length was much too small in
relation to body size for what we would regard as effective
bipedalism. And the relatively large feet don't belong. IOW
Lucy waddled.

> >So why did they maintain this very strange morphology for so long?
> Why very strange? It's basically hominoid.

It is very strange for a bipedal animal; we're constantly told
that the whole point of bipedalism was to enable a more effective
progression on the ground. As you know, I don't buy this, but it
is surprising that, once bipedalism had been achieved, the selective
pressures towards a good running and striding capability were
restrained for some 2.5 Myr.

> You acknowledge that the anatomy of Australopithecines could have had
> something to do with selection for arboreality? That gives me a lump
> in my throat,although I do think you're actually borrowing this piece
> of your theory from others who conceived of the possibillity of
> arboreality quite some time ago. There's nothing new here.

(Elaine's theory about "lumps in the throat" must have made a
deep impression on you.)

I'm ruling out the standard primate arboreality - that which
requires four prehensile limbs and enables sleeping in trees.
(The retention of such limbs would prevent bipedalism.)
I'm suggesting that one particular ability - that of climbing
_vertical_ poles where there are no side branches and minimal
hand- and foot-holds. This kind of ability is shown by the
Dayaks of Borneo when they climb up to the canopy in dense
equatorial forest, using a rope going around the tree which
enables them to lean back from the tree and "walk up" it.
(Your local telephone repair person emulates it too.) For a
hominid to achieve this without aids, it would need long arms,
short legs and large feet, which is exactly what we have in
the australos. A degree of curvature in the phalanges might
also be helpful.

I thought I had made this clear by emphasising _palm-trees_.
Obviously I hadn't. My apologies.

Another possibility, in place of (or in addition to) palm-trees
would be a dense equatorial forest (not too distant from a non-
tidal littoral, of course). The australos could then consume
a partial diet roughly like that of orangs. Their tooth enamel
would have become similarly dense, if it was not already so.
Of course, they would not have usually slept in the trees, nor
would they have taken their infants into the canopy.

The drying-out climatic phase that's supposed to have occurred
about 2.5 mya could have eliminated the equatorial forests,
thus terminating that particular form of adaptation. (I hate
suggesting anything "forced by climatic change", but as the
hominids would still have had the shellfish, it might just be

> A longer leg has its advantages in a setting were you have to cover a
> larger range (it makes bipedalism more efficient by increasing stride
> length and decreasing stride frequency)

So why was a shorter leg maintained for 2.5 Myr?

> As I already pointed out in an earlier post,shellfish does not exactly
> constitute a rich foodsource. Shellfish is particularly low in fat and
> carbohydrates and not exceptionally high in protein.

Protein can substitute for both carbohydrates and fat. Protein
is an essential part of the diet and it's glaringly missing from
inland theories of hominid evolution. How could Lucy have waddled
in the direction of the circling vultures and expect to get to the
kill before all the other predators doing the same? Why was
waddling selected for anyway?