More on Australopithecus 'knuckle-walking' characters
jgrehan at SCIENCEBUFF.ORG
Thu Aug 19 08:39:09 CDT 2004
Some further comments to add about the Richmond and Strait paper that
will only be of significance to those who accept the validity of
morphological characters independent of DNA sequence similarities. From
what I have learned subsequent to my earlier posting was that the paper
is considered to be sloppy and the character claimed as demonstrating
knuckle-walking ancestry is apparently variable in its presence and
absence in African apes. This seems to be kind of significant in that
the authors dismiss the absence of other knuckle-walking features in
Australopithecus as uninformative because they are also sometimes absent
in the African apes. So here it would be a case of a character that is
present (if it is accepted as valid - and I note that in one specimen
the feature is a reconstruction added in) it appears to not be a
necessary indicator of knuckle-walking since can be absent in
I am not aware of others in the literature taking up Richmond and
Strait's proposal, but if anyone has seen further work in that regard I
would certainly be interested to know.
In a final note, the authors use a linkage distance measurements (Fig.
2c) to produce a UPGMA cluster diagram that groups together A. anamensis
with Gorilla, then A afarensis as the sister group of that clade, and
then Pan as the next outgroup. The next outgroup comprises a
sister-group clade for Pongo and Hylobates.
The sister clade to all these groups includes a sister group
relationship between A. africanus and Homo, but other members of the
group include two monkey genera.
The figure is used to point out that the radius is remarkably
human-like, and that the earliest fossils are the most African ape-like
while later fossils more closely resemble modern humans. It seems to me
that this is a situation where overall similarity of a feature is not
necessarily correlated with phylogeny. Their reconstruction, if taken to
be phylogenetic, identifies two australopithecines as Gorilla relatives,
with chimps being more distant and the human lineage broke away before
orangutans and gibbons etc. If the phylogenetic connection is not
intended, then the similarity claimed between these taxa would not seem
to be evolutionarily informative.
In their figure 2b bivariate plot of canonical scores A afarensis
actually fits within the range for both orangutans and Gorilla, and not
chimpanzees (interesting in that orangutans are not knuckle-walkers
while gorillas are).
All that aside, the paper is terribly written (and I've written poorly
enough myself at times) and to me epitomizes the problematic nature of
systematic quality in hominid-hominoid phylogenetics.
John R. Grehan
Director of Science and Collections
Buffalo Museum of Science
1020 Humboldt Parkway
Buffalo, NY 14211-1193
email: jgrehan at sciencebuff.org
Phone: (716) 896-5200 ext 372
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