FACIAL ASYMMETRY: To illustrate the extent of the facial asymmetry in the so-called Hobbit (left), researchers created composite faces based on the left side of the face (middle) and the right side of the face (right). They concluded that the amount of asymmetry indicates that this individual had a developmental disorder. Image: 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.