More on Australopithecus 'knuckle-walking' characters

[Richard Jensen]

I should have indicated that there could be four axes for the Richmond and
Strait CVA: the number is the minimum of : (# groups-1) or number of variables
(in this case, four).

Richard Jensen wrote:

> John Grehan wrote:
>
> > 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
> > knuckle-walkers.
>
> The authors clearly inform the reader that the reconstruction played no role
> in their data analysis.
>
> >
> >
> > 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.
> >
> >
>
> This is an example of not understanding what is illustrated in Richmond and
> Strait's figure 2c.  This fugure is a UPGMA phenogram, based on Mahalanobis
> distances, and should not be (and the authors do not do this) interpreted as
> an indication of phylogeny.  The authors refer to "clades" only in the
> context of other studies, not in reference to their Fig. 2c.
>
> >
> > 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.
>
> Using this logic, some humans fit within the range of baboons!  What Fig. 2b
> illustrates are group relationships in the first two of the three dimensions
> of the CVA.  The authors note that all group centroids are, in the full
> multivariate context, significantly different from one another (except for
> baboons and Patas monkeys; this probably because only three Patas monkey
> radii were included in the analysis).  Without access to the third dimension
> (which may or may not be significant), we don't know the degree of overlap
> between Pongo and the two A. afarensis specimens.  For example, the Pongo
> specimens may be in a plane above or below those of Gorilla and the two
> afarensis specimens may be in the Gorilla plane.  Besides, the a posteriori
> probabilities for group placement indicate that both anamensis and afarensis
> are closer to Gorilla than to Pongo (not reported here; an oversight
> corrected in a response to a critique).
>
> John's objections appear to me to be based, to some extent, on
> misinterpretation of Figures 2b and 2c, and perhaps a misreading of the
> authors' comments (I find the paper rather easy reading, although some
> editing would have helped make some points more clear).
>
> Dick
> --
> Richard J. Jensen              | tel: 574-284-4674
> Department of Biology      | fax: 574-284-4716
> Saint Mary's College         | e-mail: rjensen at saintmarys.edu
> Notre Dame, IN 46556    | http://www.saintmarys.edu/~rjensen

--
Richard J. Jensen              | tel: 574-284-4674
Department of Biology      | fax: 574-284-4716
Saint Mary's College         | e-mail: rjensen at saintmarys.edu
Notre Dame, IN 46556    | http://www.saintmarys.edu/~rjensen