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Web Extra Friday, August 25, 2006

Hobbit was pygmy, scientists say

In October 2004, an international team of researchers announced that they had discovered the 18,000-year-old remains of a new species of hominid, Homo floresiensis, on the Indonesian island of Flores. In the nearly two years since then, scientists around the world have passionately debated the accuracy of that claim. The latest study to weigh in on the controversy says that the so-called hobbit is not a new hominid species, but rather a pygmy human with an unknown developmental abnormality.

Much of the debate over the hobbit has centered around interpretations of its notably small brain size, which is about one-third the size of a modern human brain. In Wednesday's Proceedings of the Natural Academy of Sciences, Robert Eckhardt, an evolutionary biologist at Pennsylvania State University in University Park, and colleagues from Indonesia, Australia, China and the United States attribute this feature to microcephaly, a condition characterized by an abnormally small head and underdeveloped brain.

The team's conclusion echoes that of another study published last May, in which an independent group of scientists compared the braincase of the hobbit with the braincases of two adult modern humans with microcephaly (see Geotimes online, May 2006). "Our two groups came up with the same conclusion," says Robert Martin, a primatologist at the Field Museum in Chicago, Ill., and co-author on the earlier study. Yet Eckhardt's group "came from a totally different direction," Martin says.

Eckhardt and his colleagues examined the remains of the hobbit and found "striking" asymmetries in its face, palate and leg bones — evidence, the team says, that the hobbit had a developmental abnormality. That, in turn, supports the idea that the hobbit's small brain size was due to microcephaly, which likely was another symptom of the abnormality.

Authors of a new study say the so-called hobbit had a developmental abnormality, as evidenced by asymmetry in its skeletal remains. The extent of the asymmetry is apparent in this image, which compares the actual hobbit skull (left), with an image created from the skull's right side and its mirror image (middle), and an image created from the skull's left side and its mirror image (right). Images are courtesy of E. Indriati (hobbit skull) and D.W. Frayer (mirror images).

The team also presented evidence to discredit the new species claim, noting that many features of the hobbit's skull are within the normal ranges of variation seen in modern humans. Some features are even similar to those of the Rampasasa pygmies, a group of a few hundred modern-day pygmies who currently live in a village near the site where the hobbit was discovered. That shows a connection between "past and present populations," Eckhardt says, and demonstrates that the hobbit is not unique.

The researchers further point out that for a new species to have evolved on Flores, it would have had to have been isolated from other populations for tens of thousands of years. However, the study authors write, this isolation is unlikely because other research has shown that Flores was connected to other inhabited land masses in the past. "Flores has been contacted by humans from the outside again and again," Eckhardt says. And even if the island wasn't connected, he says, it would have been too small to sustain a population of the size and genetic diversity needed to evolve a species.

Dean Falk, a paleoanthropologist at Florida State University in Tallahassee, says that given the research team's assertion that the hobbit is a microcephalic, "it is disappointing that they do not discuss" its brain shape in their study. In a study published in 2005, Falk compared an endocast, or model, of the hobbit's braincase to endocasts of braincases from modern humans with microcephaly (see Geotimes, May 2005). She says that their brain shapes differ completely. "The burden of proof," Falk says, is on the study's authors to make their case for microcephaly by producing a "virtual endocast" from at least one microcephalic pygmy that looks like the hobbit's endocast.

Ralph Holloway, a physical anthropologist at Columbia University in New York, likewise says that he is "not at all convinced microcephaly is the best descriptor" for the hobbit's cranial condition. Like Falk, he compared an endocast from the hobbit to endocasts from modern humans with microcephaly, and says that they do not look alike. In particular, the modern specimens have "larger cerebellar lobes relative to the cerebrum" than the hobbit specimen. Nonetheless, he says, some form of brain abnormality is still "in the running" as an explanation for the hobbit's reduced brain size.

Meanwhile, Martin stands by the microcephaly explanation and says that the idea that the hobbit could represent the earliest known case of the condition is the most interesting aspect of the hobbit find to him. "To have a microcephalic in an early human society survive into adulthood says something about the sophistication" of that society, he says, because it indicates the individual was cared for by others in the group.

Still, the debate over the true identity of the hobbit is "by no means over," Martin says. Although he is noticing more skepticism in the scientific community over the claim of the hobbit as a new species, he says that a "majority" of his colleagues still appear to support the idea. Only more fossil evidence will end the debate, Martin adds.

Holloway agrees, saying that "until another cranium is found," the question of whether the hobbit is a pygmy modern human with an abnormality or a new species cannot be fully answered. "I only hope that the political rancor ends, and further research and excavation are commenced," he says.

Jennifer Yauck

Links:
"Hobbit's species status in question," Geotimes online, Web Extra, May 19, 2006
"More 'hobbits' in Indonesia," Geotimes, December 2005
"Inside the 'hobbit's' head," Geotimes, May 2005

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