The Little Hominin That Could (Fuel Publications)

Two and a half months into 2008 and we already have three (if not more) papers out about (or with bearing on) the diminutive Flores hominin material. Indeed, interested paleoanthropologists are like the “first family” at AL 333, and the papers an interesting catastrophic event that is burying us all (not that they’re terribly bad, or anything).

As mentioned in an earlier post (“Cretins and Omomyids”), the past four years have borne witness to a huge debate on whether the ‘Homo floresiensis‘ is a new species of insular dwarfed hominin, pathological early human or what. There is no doubt about the fact that the material from Liang Bua cave, dating to as recent as 12 ka, is small. What has been most hotly debated is the etiology of the unique features of the LB-1 skull, such as (From Brown et al. 2004):

  • Cranial capacity estimated ~400 cc
  • Reduced parietal lobe development in the brain (relative to H. sapiens)
  • Long, low cranial vault
  • Maximum cranial breadth just above the mastoids
  • Prominent nasal pillars
  • Mesially rotated mandibular P4s
  • Posteriorly inclined mandibular symphysis (i.e. no chin)

Arguably these traits distinguish LB1 from modern humans (although one of my mandibular premolars is fairly mesially rotated), and more closely aligns it with earlier Homo taxa, e.g. H. habilis/erectus. Last year, Hershkovitz et al. made a pretty strong case for many of these ‘distinguishing’ characters being the result of Laron syndrome.

The first floresiensis-related paper this year was Obendorf et al.’s diagnosis of myxoedematous cretinism. According to them, thyroid malfunction resulted in the anamolous Liang Bua morphology. Their basis for this diagnosis was what they perceived to be an enlarged pituitary fossa, based on a picture of a CT scan. Though interesting, this hypothesis was nevertheless blown out of the water, as many parties–many of whom have seen the actual specimen–denied existence of an enlarged pituitary fossa. Bummer there.

A few days later, Berger et al. reported on diminutive humans (dating to 3-0.9 ka)from caves on the island of Palau. Authors noted some similarities to the Liang Bua material. They suggested that, since their material is undoubtedly human, but similarly tiny like floresiensis, many of the unique features of floresiensis might really be a function of their diminutive size, and that new species designation might not be appropriate. Of course, most of the LB 1 anomalies are cranial, and Palau crania are not yet observable, so Palau, at the moment, has little bearing on Liang Bua (viz. LB 1 and 6).

Finally, Gordon et al. today published a paper in which they used craniometric morphology of LB 1 to establish its taxonomic affinities. Their analysis shows that LB 1 falls outside their human sample, and clusters well with H. erectus, in a broad sense, and to a lesser extent with H. habilis. Thus, contra those who posit that LB 1 is human, but unique because of pathology or pleiotropic effects of small size, Gordon et al. support the idea that LB 1 (and therefore, all diminutive Liang Bua hominins) represents a new species, derived from H. erectus or habilis (cf. African or Dmanisi erectines). Their compartive sample included 2500 modern human crania from all over the globe and 30 hominin crania.

I suppose that I have to take issue with the sample. Comparing LB 1 to modern human crania from all over the globe is a bit like comparing a 15 ka Javanese apple to a modern, international fruit basket (I admit I’m embellishing). On the other hand, comparing it to a wide diversity of human crania might be generous, as it increases the range of variation, making it easier for LB 1 to fit in. But they did not address the issue of pathology very well. They write:

With regard to microcephaly, it should be noted that in the shape analysis performed here, LB1 cranial shape is shown to differ significantly from the modern human comparative sample (and from fossil H. sapiens and Neanderthals) and to be very close in morphological space to non-Asian H. erectus specimens (D2700 and KNM-ER 3733). And H. habilis specimens (KNM-ER 1813 and OH 24). LB1 and the non-Asian H. erectus specimens are much closer than the average pairwise distance between modern human crania, and standardized residuals of LB1 from the estimated non-Asian H. erectus and H. habilis scaling relationshps average 1.38 and 1.21 standard deviations away from expected shape, respectively . . . well within the range of population-level variation (Table 1). Thus, if microcephaly is responsible for the extremely small size of the LB1 cranium, of all possible ways that microcephaly could cause LB1 cranial shape to differ from that modern humans and for these six variables, it happens to differ in the same way that earlier Homo species differ from modern humans [p. 4654].

Ok, so here they sort of test the hypothesis that LB 1 is craniometrically like a microcephalic by comparing it to a large sample of non-microcephalics–now that’s comparing ancient apples to a Harry and David exotic fruit basket! To my knowledge, Argue et al. (2006) are the only ones to compare craniometrics of Liang Bua to any microcephalics. Their findings (see their Figs. 3 and 4) show that, as in the Gordon et al. study, LB 1 is most close to ER 3733 and OH 24. But, this study looks at only two microcephalics (though they compare LB 1 to these in separate analyses…), and these two individuals are on the extreme margins of a wide range of human variation. Moreover, there are myriad ways to be microcephalic, and it is unclear how different ways might affect craniometric variation.

That Gordon et al. and Argue et al. agree that LB 1 is craniometrically very similar to ER 3733 and OH 24 might not be insignificant. But Gordon et al. make the assumption that modern human microcephalics are craniometrically no different from non-pathological humans. While the Argue study suggests microcephalics might not be too different, they do show they are nonetheless on the outskirts of human variation (when also compared to fossil hominins…); moreover their microcephalic sample is very small. In order for Gordon et al. to reject microcephaly, they need to satisfactorily establish that microcephalics are not too different from humans cranimetrically. And that requires a larger sample of microcephalics. Hey, there’s a handful of microcephalic skulls (get it–“handful,” cuz they’re micro…) in my lab, maybe I’ll undertake this endeavor, after I get done with my billion other projects….

Anyway, apparently Hershkovitz et al. didn’t officially settle the Liang Bua issue. It’ll be interesting to see what Falk et al. bring to the table in Columbus in a few weeks. A never-ending saga . . .
References
Argue D, Donlon D, Groves C, and Wright R. 2006. Homo floresiensis: Microcephalic, pygmoid, Australopithecus, or Homo? J Hum Evol 51: 360-374.

Berger L, Churchill S, de Klerk B, Quinn R. 2008. Small-bodied humans from Palau, Micronesia. PLoS ONE 3: e1780

Brown P, Sutikna T, Morwood M, Soejono R, Jatmiko, Wayhu Saptomo E, Awe Due R. 2004. A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia. Nature 431: 1055-1061.

Gordon A, Nevell L, Wood B. 2008. The Homo floresiensis cranium (LB1): Size, scaling and early Homo affinities. Proc Nat Acad Sci 105: 4650-4655.

Hershkovitz I, Kornreich L, Laron Z. 2007. Comparative skeletal features between Homo floresiensis and patients with primary growth hormone insensitivity (Laron Syndrome). Am J Phys Anthropol 134: 198-208.

Obendorf PJ, Oxnard CE and Kefford BJ, in press. Are the small human-like found on Flores human endemic cretins? Proc R Soc B xx: 1-10.

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