Pygmoid, Australopithecus, Homo, yada yada…

4 minute read

I can't help noting the contrast between these two quotes. First, from Argue et al. (2006:18-19):

A cranial morphometric and morphological comparison of LB1 with microcephalic individuals suggests that LB1 is unlikely to be a microcephalic H. sapiens, at least not of the MOPD II type. In the craniometric analyses, the Minoan and Sano 3 microcephalics are within the range of H. sapiens, although the Minoan is on the edge of the range of this species. LB1 is outside the range of H. sapiens and separated from the two microcephalics. For the microcephalics to cluster with LB1 in the analyses, they would have to possess a greater degree of prognathism, a lower vault, and wider biauricular breadths, which one might consider an unlikely set of characteristics for H. sapiens. We note, however, that we were only able to include two microcephalic individuals in the metric analyses for want of published data. Microcephaly is an extremely heterogeneous condition and, while our results are suggestive, it may be that they would differ should a larger sample of microcephalics be studied.
When the cranial morphology of MOPD II individuals is compared to that of LB1, however, the only condition they have in common is a small cranial capacity. In no other way does LB1's cranial morphology correspond to that of MOPD II. Further, except for a bowing of the tibia, LB1 does not display any of the postcranial morphologies commonly found in these individuals. Likewise, LB1 separates from the LT 'pygmoid' in the cranial metric analyses and does not display its modern human morphological features. LB1 is separate from the Andaman sample in the cranial analyses and does not reflect the postcranial proportions of any African pygmy populations. It would appear unlikely, then, that LB1 is either a microcephalic or pygmoid H. sapiens.

And then this quote from Richards (2006:15):

Many of the post-cranial features described for the Flores remains (Brown et al., 2004; Morwood et al., 2005) are consistent with those found in human populations that have undergone stature reduction by way of a modification of the GH-IGF-I axis. Brain size in humans can be reduced through the MCPH gene family or changes in IGFs and GHs (via GHRH-R inactivation) to the size of that found in H. floresiensis without significant impacts on the viability of a majority of the affected individuals. Genetic mutations that produce such reductions can be present at high frequencies in small, consanguineous groups in relatively isolated contexts. MCPH individuals show developmental delay and, in some, a reduction in stature. However, despite considerable effort I have been unable to uncover data on how MCPH impacts somatic development and, by extension, how this might impact craniofacial development. I have also been unable to discern how changes resulting from MCPH might interact with developmental modifications expressed in GH-IGF-I axis defects. Nevertheless, based on available data, a basic model that accounts for the morphology of H. floresiensis can be constructed.
Such a scenario would account for the reduced body and brain size found in the LB1-LB9 individuals, but it does not fully reveal the underlying biology of the craniofacial skeleton. Any attempt to reveal this biology and construct a basic explanatory model is complicated by the lack of: (1) individuals possessing a combined GH-IGF-I/MCPH malformation; (2) documentation on specific changes and geographic variation in skeleto-dental features in individuals possessing either of these conditions and (3) knowledge of the change that results in the modification of the GH-IGF-I axis in pygmy populations.

Completely opposite conclusions!

Now, Richards focuses his paper far more on the medical and genetics literature related to microcephaly and small body size; Argue et al. include metric comparisons with a small number of microcephalic humans as well as normal humans and fossil hominids.

Richards discusses a wide range of microcephaly-inducing pathologies; Argue and colleagues also discuss a broad range but focus their comparisons on one. Richards doesn't really provide any comparisons.

Argue and colleagues conclude that LB1 is not any of the other things, because it falls metrically (and nonmetrically) outside the range of the other things. Richards proposes that it falls outside the range of other things because it has a combination of two things.

Richards relies on parsimony for his arguments about the phylogenetic relationships of LB1 -- in particular the shared features with modern humans that would have to have evolved in parallel on Flores if that population emerged from some earlier hominid. Argue and colleagues discuss some parallelisms with modern humans, but do not apply any arguments based on parsimony.

All this goes to explain how two groups of people can look at exactly the same data and come to opposite conclusions. I suppose I should be worried that I read all this and come to yet another conclusion.


Argue D, Donlon D, Groves C, Wright R. 2006. Homo floresiensis: Microcephalic, pygmoid, Australopithecus, or Homo? J Hum Evol in press. DOI link

Richards GD. 2006. Genetic, physiologic and ecogeographic factors contributing to variation in Homo sapiens: Homo floresiensis reconsidered. J Evol Biol in press DOI link