knuckle-walking (was: hominid classification)

[John Grehan]

> Why would you want to cite Dainton (2001)----just because he argues
> against Richmond and Strait?  

The point is that there is more than one view on the nature of the
evidence.

The latter authors (in their response to
> Dainton, 2001) even agree with him that it is possible that knuckle-
> walking could have evolved in parallel between Gorilla and a
Pan-hominid
> clade (although questioning the parsimony of such an argument).

It almost seems that anything is 'possible' to maintain the Homo-African
ape argument.

> Dainton's main argument is that Gorilla evolved knuckle walking
separately
> from a Pan-hominid clade.  I don't see how that helps your viewpoint
on an
> orangutan-hominid clade.  Talk about red herrings!!

Dainton (p. 324) argues that the traits used by Richmond and Strait are
not uniquely associated with knuckle-walking. He may or may not be
right. The point is that Richmond and Strait's view is not without
contestation.
> 
>       Quite apart from the arguments over knuckle-walking (per se),
the
> point is that the morphology of the distal radius is very similar (in
more
> than one way) between Gorilla, Pan, and early Australopithecus----and
> quite different from that of the Asian apes.  

That might be correct. It remains to be seen whether the similarities of
morphology in distal radius constitute synapomorphic conditions or just
overall similarity. In FIG 2b the authors seem to show an overlap
between afarensis and both Gorilla and Pongo in their canonical variate
analysis.

And frankly, I can't help
> but wonder if there are plenty of morphological synapomorphies for the
> African clade, but your request for information from primate
> paleosystematists somehow "put them off", and that they just didn't
think
> it was worth their time responding.  Frankly, I'm getting to that
point
> myself, so don't be surprised if I abandon this particular thread.

There is nothing in the literature for synapomorphies encompassing
humans-chimps, and australopithecines. That's the real problem. Perhaps
the specialists don't think this is something worth responding, but it
seems to me it's a basic systematic problem for hominid evolution.

There are morphological characters proposed for humans and chimpanzees -
but the number is very low compared with orangutans, and humans and
African apes with a larger number but again lower than for humans and
orangutans. And many of those characters are problematic. Richmond and
Strait cite fusion of the os central with the scaphoid as "one of the
few derived morphological characteristics shared by African apes and
humans, is an adaptation to resist weight-bearing stresses and improve
the stability of the hand in terrestrial quadripedalism". Sounds good,
but in humans may actually resorb the os centrale before it develops
much at all. So the claim for this character is problematic at best.

As long as I am having trouble finding any (let along one or even a few)
synapomorphies for humans-chimps-australopithecines I will keep raising
the program (especially when I can cite 14 for
humans-orangutans-australopithecines) - whether or not that causes
discomfort for Ken or anyone else (not that I am into causing
discomfort!). 


>            ------ Ken Kinman
> P.S.  And I do think fossils are important for phylogeny, but for
those
> which are extremely fragmentary (including a number of hominids),
their
> usefulness is somewhat limited (and certainly not JUST because they
don't
> have recoverable DNA).

I agree their usefulness may be limited, but if they are to have any use
at all they must be objects directly comparable to the living. If
morphology is so unreliable that it must be rejected when it conflicts
with DNA base sequence similarities then fossils are rendered completely
uninformative about phylogeny since nothing in the fossil record is
reliable. A fossil might be a primate or it might not, but without
genetics once could argue from a DNA sequence bias that we really don't
know at all.