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Precladistic systematics?

Posted by Vargas on 14 Mar 2008 at 02:26 GMT

My opinion, from a paleobiologist's perpective, on the Berger et al. paper:

It is clear that the palau fossils are a very interesting new form, indeed probably a new species of Homo. However, much controversy has yet to be cleared away.

Berger et al. state as "plain fact" that these tiny Palauans are descended from H. sapiens. This is an affirmation about the phylogenetic relationships of these new fossil forms. This affirmation may seem at odds with some primitive traits of this new form, as well as traits exclusively shared with H. floresiensis. These traits are dismissed by Berger et al as taxonomically insignificant convergences and reversions, such as could be produced by an epigenetic correlate of small body size.

However, without a phylogenetic analysis, Berger hasn't really presented the evidence to justify his affirmation that these tiny Palauans are H. sapiens. In fact, a mix of human autapomorphies and primitive traits suggest a species that may be closely related to H. sapiens, sharing many traits, yet still diverged previous to modern H sapiens (such as Palauans) that lack these primitive traits.

To discard this possibility and prove that tiny Palauans are H. sapiens, Berger et al. would have had to show that their tiny Palauans are phylogenetically nested within H. sapiens. However they did not make a phylogenetic analysis (despite disposing of several specimens and good morphological data)

Without that, they are simply preferring hypotheses of convergence or reversal rather than homology for the primitive traits, which is, in fact, contra-parsimony as an initial assumption.

A little PAUP on the morphological traits is a standard procedure in systematics and paleontology when describing a new fossil form with evolutionary relevance.

Statements such as "We feel that the most parsimonious, and most reasonable, interpretation of the human fossil assemblage from Palau is that they derive from a small-bodied population of H. sapiens" are not acceptable as a substitute for actual phylogenetic analysis using parsimony. If Berger et al did that analysis, they would KNOW, rather than FEEL, whether the affirmation "tiny palauans are H. sapiens" indeed stands out as the most parsimonious hypothesis.

Alexander Vargas
Postdoctoral Research Associate
Department of Ecology and Evolution
Yale University

RE: Precladistic systematics?

Vargas replied to Vargas on 05 Sep 2008 at 18:59 GMT

Well, it seems that Berger et al could not even be trusted on their basic description of having found small-sized humans with small brains, as reported. I was only complaining about lack of phylogenetic analysis while assuming their basic description was OK; Yet apparently this paper was more fundamentally flawed than my good will was accepting; the evidence was not only too fragmentary for phylogentic analysis, it was too fragmentary to demonstrate small size or microcephaly. These were bones simply of ancient local humans! See the new paper by Fitzpatrick et al. in this Journal.