Tuesday, May 23, 2006

Homo floresiensis: New Species or Modern Human?

One of the more fascinating debates in anthropology right now is the explanation of LB1, a.k.a. "the Hobbit," –the proposed new hominid species Homo floresiensis. Found in 2003 in the Liang Bua Cave on the island of Flores in Indonesia.

There's been some recent buzz in the journal Science as, first; Falk et al (2005) reported that the specimen may be that of a dwarf species descended from Homo erectus. Then; Martin et al concluded that LB1 isn't a new species at all, but rather a microcephalic modern human. Falk et al used endocast reconstructions of LB1, a chimpanzee, H. erectus (ZKD XI), a modern human, and microcephalic. Endocasts are 3 dimensional representations of the inside of the braincase and reveal structures like sulci, vessels, and such and also cranial capacity can be derived. Falk et al used female comparators in all cases except the microcephalic and possibly LB1 itself, which has recently been described as a probable male (Culotta 2006).

Falk included the microcephalic because there had been some sharp criticisms of those that heralded the "discovery of a new species of hominid," which insisted that a sample size of one is not cause for excitement and because the find could simply be the result of a pathological cause not evolution. Microcephalic implies that the individual has an abnormally small head and can be caused by a wide range of conditions.

Martin et al (2006) responded to Falk et al with a critique that suggested their microcephalic sample (AMNH 2792a) was inappropriate since it was of a male that only reached an age of 10 years and LB1 is of an adult. Microcephalics can be classed as both "high-functioning" and "low-functioning" and the latter rarely reach adulthood. Martin et al suggest that this is reason enough to eliminate AMNH as a comparator. Falk et al responded that Martin et al used incomplete line drawings that provided little detail and point out that death among low-functioning microcephalics "typically occurs within the first several years of life." My first thought reading that was if my own daughter were to die for any reason at age 10, I don't think I could quantify her life with terms that exceed "several" or "few" when referring to the number of years I spent with her.

But hair-splitting aside, Falk et al also point out that LB1's endocast was "highly convoluted" in appearance while the microcephalic endocasts that Martin et al provided in their line drawings did not appear so. They also draw point out some other morphological differences with LB1 and Martin et al's comparators. Martin et al point out that the cranial capacity of the single microcephalic (ANMH) that Falk et al used was abnormally low for the microcephalic mean, to which LB1 is closer to.

At the end of the day, we are left with: the fact that LB1 is a sample size of one with regards to cranial artifacts, though additional finds were located in the cave from other individuals; the cranial capacity is consistent with the microcephalic mean of modern humans; stone tools found at the site were consistent with those of full-sized Homo sapiens; and, as Martin et al suggest, it may be that the site may even have been culturally influenced as a place where sufferers of microcephaly were brought by society to which they belonged. If a pathological cause in antiquity created multiple microcephalics, is it so inconceivable that that their culture would find them different or even special? If they were modern humans, as Martin et al suggest, then I think we have a few modern day analogs that can be used to demonstrate the tendency for humans to single out those they find different.


Culotta, E. (2006, 19 May). How the Hobbit Shrugged: Tiny Hominid's Story Takes New Turn. Science, 312(5776), 983-984.
Falk, D., Hildebolt, C., Smith, K., Morwood, M., Sutikna, T., Brown, P., et al. (2005, 8 April). The Brain of LB1, Homo floresiensis. Science, 308(5719), 242-245.
Falk, D., Hildebolt, C., Smith, K., Morwood, M., Sutikna, T., Brown, P., et al. (2006, 19 May). Response to Comment on "The Brain of LB1, Homo floresiensis." Science, 312(5776), 999.
Martin, R., Maclarnon, A., Phillips, J., Dussubieux, L., Williams, P., & Dobyns, W. (2006, 19 May). Comment on "The Brain of LB1, Homo floresiensis. [Full Text Free] Science, 312(5776), 999.

2 Epigraphic Artifacts:

Torbjörn Larsson said...

As many has said before, currently it comes down to probability and parsimonity. Perhaps the fact that initially Neanderthals were modelled from sick individuals is another input that tells us to err on the conservative side.

AFAIK in this case the stone tools doesn't necessarily mean more than ability to collect discarded tools for whatever reason; AFAIK other producers were close at hand.

AFAIK there were several remains with similar morphology, including similar jaws. Which leads to some questions that gives the issue of parsimony problems. Do we know if similar microcephalics survive to be this old? Do we know if microcephaly can be so common? Why are all remains such?

I am not sure which conclusion is best at the moment.

Torbjörn Larsson said...

"Why are all remains such?"

Which question the post gave an answer to, of course.

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