Two years ago paleoanthropologists were knocked for a loop by the discovery of an 18,000-year-old human skeleton, later nicknamed the Hobbit, on the Indonesian island of Flores. Hardly more than a meter tall, with a skull the size of a grapefruit, the Hobbit did not seem like Homo sapiens to its discoverers, and neither did the much more fragmentary remains unearthed alongside it.
The Hobbit's small braincase and broad pelvis are characteristics normally associated with much older hominid species, but in other ways its skull resembled that of the more recent Homo erectus. The Australian-led group that unearthed the specimen, also known as LB1, finally declared it a new species, Homo floresiensis, which they speculated had descended from H. erectus and shrank in response to the evolutionary pressures of life on a small island. If true, it would be a remarkable find: a hominid contemporaneous with modern humans up until perhaps 12,000 years ago. "Until this, everybody thought the only game in town [that recently] from a hominid point-of-view was Homo sapiens," says paleoneurologist Dean Falk of Florida State University.
Other researchers are not convinced, countering that the Hobbit was more likely a Homo sapiens with a broad pathological condition called microcephaly, in which the brain is abnormally small. Inbreeding could have made such individuals common, argues Robert Martin of the Field Museum in Chicago.
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A large part of the debate has focused on the skull--specifically, whether it is malformed or not. Falk and her coworkers reconstructed LB1's brain shape based on CT scans of the skull interior. They compared this shape to a variety of other cases, including chimp, pygmy H. sapiens and a microcephalic. LB1's estimated brain volume, 417 cubic centimeters, would be small for a H. sapiens of that size, but it follows the trend of the more primitive australopithecines, they reported. The brain is most closely matched to H. erectus, based on its relatively large temporal lobes, including big convolutions in an area thought to be key for initiating and planning action, they concluded. "This is a fancy brain," Falk notes. "It has derived features that are special and different. I've never seen anything like it."
Other groups drew their own comparisons. Some, including Martin and his collaborators, cited instances of microcephalics who had enlargements in the temporal lobe similar to LB1's or otherwise resembled it. Unfortunately, none of the groups presented their results in the same format, which prevented any unequivocal comparison. More recently, in August, another team brought up a laundry list of nits to pick: the skull's asymmetry--a hallmark of developmental problems, they claimed; its lack of chin, which they argued was a trait that occurs with some frequency in modern Australomelanesians; and shallow muscle attachment sites on the limb bones, presumed responsible for LB1's untwisted upper arm bone. Proponents of the H. floresiensis classification see these traits as primitive, not abnormal--except for the asymmetry of the skull, which the discoverers say got a little squished after millennia beneath limestone.
Both sides could use another skull. If a microcephalic turned up that looked like LB1, "then the game would be over," Falk acknowledges. But if researchers could dig up one more small Hobbit skull, perhaps on another Indonesian island, they might yet silence the naysayers.
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