More Tininess From the Malay Archipelago

I've been blogging on nothing but code lately, so here's a "quick" paleo-post.

"Hobbits": Primitives or Pinheads?

The anthropological world was shocked several years ago by the discovery of a relatively recent pygmy species of stem-human, popularly dubbed "hobbits" and more technically dubbed Homo floresiensis (Brown et al. 2004). Known from subfossil remains of several individuals from the island of Flores (Morwood, Brown et al. 2004), including one nearly complete skeleton including the skull (the holotype specimen), these people stood barely over a meter in height, shorter than any modern pygmy humans. They survived at least until 13,000 years before present (Morwood, Soejono et al. 2004), and, judging from the one skull, they had extremely small brains for such late-surviving Homo (380 cc—we average around 1400 cc and even Australopithecus africanus averaged in the 400s). They had other primitive features as well, such as chinless jaws, a low twist in the forearm bones (Ibid.), robust leg bones (Ibid.), a chimp-like wrist (Tocheri et al. 2007), and some features of the teeth.

But not everyone agrees that the Floresian "hobbits" are a separate species. Various researchers have proposed that they are, in fact, pygmy Homo sapiens and that at least some individuals, including the holotype, have a pathological condition that includes microcephaly, a.k.a. "pinheadedness" (Martin et al. 2006, Jacob et al. 2006). After all, at least some of the supposedly diagnostic features, such as chinlessness, are present in some members of our own species (Jacob et al. 2006). But others insist that there are genuine primitive features in the Floresian specimens that cannot be explained by microcephaly or dwarfism (Falk et al. 2005, Falk et al. 2006, Argue et al. 2006).

A New Discovery

Until recently, the Floresians' size distinguished them from H. sapiens. But that was before this week's publication (Berger et al. 2008; open access) of some very recent (1400 to 2900 years B.P.) pygmy/dwarf fossils from Palau. More work needs to be done to free these fossils from the limestone they were found in, but they seem to be Homo sapiens proper, high-domed skulls and all. What's really interesting is that, like the Floresian "hobbits", the Palauans are smaller than any living population of H. sapiens. But unlike the "hobbit" holotype, their cranial capacity is not abnormally low.

Berger et al. note that the Palau specimens have some supposedly "primitive" features that may in fact be related to size, such as proportionally large teeth (megadontia) and chinless mandibles. The authors don't firmly ally themselves with either camp, but note that at least some of the supposed diagnostic features of H. floresiensis are probably phylogenetically uninformative, merely being results of dwarfism.

Thoughts

Personally, while I'm no expert in any the fields involved, I find the arguments that the Floresians are pathological, pygmy H. sapiens unconvincing. For one thing, people afflicted with the proposed diseases don't actually look like the "hobbits" except in having small brains. For another, asymmetry that was ascribed to pathology seems more likely to me to be a preservational artifact. Look at just about any fossil skull face-on—most of them are asymmetrical.

But more damning are the limb characters, which no known pathology can explain. (Did they have some kind of "ape-itis" in addition to microcephaly?) Fact is, I think that if H. floresiensis were 130,000 years old instead of 13,000, nobody would even contest the idea that they weren't H. sapiens. And morphology deserves more weight than chronology in matters of systematics.

References

• Argue, D., D. Donlon, C. Groves and R. Wright (2006 October 4). Homo floresiensis: microcephalic, pygmoid, Australopithecus, or Homo? Journal of Human Evolution 51(4):360–374. doi:10.1016/j.jhevol.2006.04.013
• Berger, L. R., S. E. Churchill, B. De Klerk and R. L. Quinn (2008 March 12). Small-bodied humans from Palau, Micronesia. PLoS ONE 3(3):e1780. doi:10.1371/journal.pone.0001780
• Brown, P., T. Sutkina, M. J. Morwood, R. P. Soejono, Jatmiko, E. Wayhu Saptomo and Rokus Awe Due. (2004 October 28). A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia. Nature 431:1055–1061. doi:10.1038/nature02999
• Falk, D., C. Hildebolt, K. Smith, M. J. Morwood, T. Sutkina, P. Brown, Jatmiko, E. Wayhu Saptomo, B. Brunsden and F. Prior (2005 April 8). The brain of LB1, Homo floresiensis. Science 308(5719):242–245. doi:10.1126/science.1109727
• Falk, D., C. Hildebolt, K. Smith, M. J. Morwood, T. Sutkina, P. Brown, Jatmiko, E. Wayhu Saptomo, B. Brunsden and F. Prior (2006 May 19). Response to comment on "The brain of LB1, Homo floresiensis". Science 312(5776):999. doi:10.1126/science.1124972
• Jacob, T. E., Indriati, R. P. Soejono, K. Hsü, D. W. Frayer, R. B. Eckhardt, A. J. Kuperavage, A. Thorne and M. Hennenberg (2006 September 5). Pygmoid Australomelanesian Homo sapiens skeletal remains from Liang Bua, Flores: population affinities and pathological abnormalities. Proceedings of the National Academy of Sciences of the United States of America 103(36):13421–13426. doi:10.1073/pnas.0605563103
• Martin, R. D., A. M. MacLarnon, J. L. Philips, L. Dussubieux, P. R. Williams and W. B. Dobyns (2006 May 19). Comment on "The brain of LB1, Homo floresiensis". Science 312(5776):999. doi:10.1126/science.1121144
• Morwood, M. J., P. Brown, Jatmiko, T. Sutkina, E. Wahyu Saptomo, K. E. Westaway, Rokus Awe Due, R. G. Roberts, T. Maeda, S. Wasisto and T. Djubiantono (2005 October 13). Further evidence for small-bodied hominins from the Late Plesitocene of Flores, Indonesia. Nature 437:1012–1017. doi:10.1038/nature04022
• Morwood, M. J., R. P. Soejono, R. G. Roberts, T. Sutkina, C. S. M. Turney, K. E. Westaway, W. J. Rink, J.-x. Zhao, G. D. van den Bergh, Rokus Awe Due, D. R. Hobbs, M. W. Moore, M. I. Bird and L. K. Fifield (2004 October 28). Archaeology and age of a new hominin from Flores in eastern Indonesia. Nature 431:1087–1091. doi:10.1038/nature02956
• Tocheri, M. W., C. M. Orr, S. G. Larson, T. Sutikna, Jatmiko, E. Wahyu Saptomo, Rokus Awe Due, T. Djubiantono, M. J. Morwood and W. L. Jungers (2007 September 21). The primitive wrist of Homo floresiensis and its implications for hominin evolution. Science 317(5845):1743–1745. doi:10.1126/science.1147143