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This article is from the In-Depth Report The Hobbit: 10 Years Later

Hobbit Hubbub

New study stirs debate over mini human species
hobbit asymmetry



COURTESY OF PNAS
In October 2004 paleoanthropologists announced they had discovered the partial skeleton of a human species new to science that lived as recently as 12,000 years ago. The bones, recovered from a cave called Liang Bua on the island of Flores in the Indonesian archipelago, revealed a creature little more than a meter tall, with a brain a third the size of our own. Scientifically dubbed Homo floresiensis and affectionately nicknamed the Hobbit, the find was an instant sensation.

But experts have been at loggerheads over the remains ever since. At issue is whether they belong to a new species at all, or rather to a diseased member of our own kind. To that end, a long-awaited analysis by a vocal group of skeptics was published online today by the Proceedings of the National Academy of Sciences.

In the paper, Teuku Jacob of Gadjah Mada University in Indonesia, and his colleagues challenge the original interpretation of the bones as those of a species descended from Homo erectus that evolved its petite size as an adaptive response to being stranded on a small island with limited resources. (Lacking contact with other hominids, so this scenario goes, the marooned Floresians set off on their own evolutionary course.) They believe that the skeleton, known as LB1, is that of a pygmy H. sapiens with a developmental disorder that produced, among other things, its diminutive brain (a condition known as microcephaly).

Jacob's team contends that the initial studies, led by Peter Brown and Michael Morwood of the University of New England in Armidale, Australia, fail to explain how such small-brained people could have made tools previously associated only with the much larger-brained H. sapiens. The group also doubts that humans could have evolved in isolation on Flores, given that the elephantlike Stegodon was able to colonize the island more than once.

Moreover, the Hobbit detractors say, a number of the anatomical characteristics said to distinguish LB1 and the other specimens from H. sapiens--the rotated premolars and the absence of a chin, for example--are found in modern Australomelanesians, including a population of pygmies that lives near Liang Bua cave today. Other traits, in their view, are indicative of development gone awry--the teeny braincase, asymmetries in the skull and skeletal bones, and weakly marked muscle attachment sites on the limb bones, among them.

To illustrate the extent of the facial asymmetry in LB1, team member David W. Frayer of the University of Kansas split a digital photo of the skull down the middle and then doubled and mirrored each side to create two composite faces, one based on the left side and one based on the right. The result was two very different looking faces. "While most faces are not perfectly symmetrical, asymmetry of the facial skeleton that exceeds about 1 percent is unusual," co-author Robert Eckhardt of Pennsylvania State University comments. The asymmetry on LB1's visage "exceeds clinical norms," according to the report. "LB1 is not a normal member of a new species, but an abnormal member of our own," Eckhardt states.

Members of the team that found and described the fossils dismiss the new analysis. Morwood counters that the tools from Liang Bua closely resemble tools found at another site on Flores that are up to 880,000 years old, indicating uninterrupted human occupation and cultural tradition on the island. "Such artifacts are not the exclusive prerogative of modern human knappers," he insists. Furthermore, although Stegodon did colonize Flores a second time, following a massive volcanic eruption that wiped out the first Stegodon there around 900,000 years ago, it appears to have established itself for the long haul the second time around: the dwarfed Stegodon at Liang Bua that is coeval with the little human remains is believed to be the direct descendant of the larger species that arrived hundreds of thousands of years prior.

Harsher words come from Brown, who retorts that the paper "provides absolutely no evidence that the diagnostic features in H. floresiensis are replicated in modern humans." All modern humans have chins, he insists, including microcephalics and the living Flores pygmies to whom Jacob and his co-authors refer. Neither is Brown persuaded by the analysis of LB1's facial asymmetry. "The skeleton was buried under nine meters of sediment and there was some slight distortion. I know because I put it together," he comments. "Their claims about the asymmetry being the result of abnormal growth are fiction."

Other researchers who have studied the remains are likewise critical of the new study. Susan Larson of Stony Brook University, who is analyzing the shoulder anatomy of the Liang Bua bones, disputes the authors' contention that LB1's limb bone muscle markings signify underdeveloped shoulder muscles. The authors suppose that impoverished muscles are part of the reason why LB1's upper arm bone is so straight, instead of being twisted between the elbow and shoulder like a normal modern human's humerus. But "it has been demonstrated that there is no simple relationship between size or complexity of muscle markings and the size or strength of the muscles," Larson observes. "There is no evidence that [Homo floresiensis] had weak muscles." Furthermore, she notes, most of the twisting of the humerus seen in modern humans develops in the womb, before any muscular forces can influence it. Larson's own work suggests that LB1's relatively straight humerus is a primitive characteristic, held over from a time when hominids were still transitioning from a shoulder built for quadrupedal locomotion to one possibly optimized for throwing and/or bipedal endurance running.

William Jungers, also at Stony Brook, calls the skeptics' description of the skeletal remains "a flimsy house of cards." Not only do the stature and limb proportions evident in the Liang Bua remains distinguish Homo floresiensis from all other known hominids, he says, but contrary to the claims that cross sections of the leg bones reveal pathological abnormalities, his own analyses indicate that they are normal.

For his part, Brown points out that he has since moved away from the idea that Homo floresiensis evolved its bantam body and brain proportions as a result of being isolated on a small island. More likely, he suggests, its ancestors were already small when they arrived on Flores. He notes that a paper upholding the new species interpretation, by Debbie Argue of the Australian National University and her colleagues, was recently accepted for publication in the Journal of Human Evolution.

Complicating matters is the fact that only one skull has been found at Liang Bua--LB1's. The other bones from the site fit the same small body size profile (in fact, some appear to come from individuals even smaller than LB1), but body size reveals nothing about brain size. Indeed, although modern pygmies have small bodies, their brains are comparable in size to those of large-bodied people. Paleoanthropologists mostly agree that the discovery of another small-brained hominid at Liang Bua would erase any doubts about the new species interpretation. But the Indonesian government has closed the cave to further excavation for the time being, following a bitter dispute between the discoverers and rival scientists, including Jacob. DNA retrieval and analysis, too, seems unlikely, because DNA tends to degrade rapidly under warm, wet conditions.

Morwood is thus searching for other sites in the Indonesian archipelago that could contain Homo floresiensis remains. Clues may also come from comparisons with fossils of small-bodied Homo erectus that have been recovered at a site called Dmanisi in the Republic of Georgia. Meanwhile, the skeptics will continue their quest for a specific syndrome that fits LB1's particular constellation of traits. That is to say, the Hobbit wars will doubtless continue for quite some time to come.

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