The models of microcephalics represented males and females, children and adults, and come from all over the world.
"We wanted a really diverse sample," Falk said.
The researchers found two characteristics—in addition to small size—that distinguish microcephalic brains: The bottom part sticks out in the back, and the region behind the forehead is unusually narrow.
When the team compared LB1 to the diverse sample of microcephalics and normal humans, it most closely fit the model of normal humans.
"It's not microcephalic," Falk said. "In fact it's the opposite. Except for brain size, the features are the antithesis of microcephaly."
In the study, published in this week's issue of the Proceedings of the National Academy of Sciences, Falk's team adds that LB1's tiny brain size and other brain characteristics "are consistent with its assignment to a separate species."
(See a National Geographic magazine feature: "Flores Find: The People That Time Forgot.")
Falk's team also compared the models to a skull from South Africa that a separate research team said resembled LB1; the computer model classified it as microcephalic.
The team was unable to obtain information about another microcephalic skull that a third research team said resembled the hobbit and thus supported the argument that LB1 was diseased, not a new species.
"Unfortunately, we were not able to address that claim," Falk said.
Robert Martin is curator of biological anthropology at the Field Museum in Chicago and a co-author of two papers that argue LB1 was a diseased modern human.
The new analysis fails to change his stance.
Most important, Martin said, is a discrepancy between his and Falk's team on the classification of the skull from South Africa, known as Basuto woman.
Martin said his team analyzed the skull with the "exact same methods" used for an analysis of different skulls published by Falk's team in Science in 2005. The 2005 paper set off the debate between the two research teams.
(Related: "'Hobbit' Brains Were Small but Smart, Study Says" [March 3, 2005].)
According to the Martin team's results, published online last September in the journal Anatomical Record, the brain of Basuto woman, a known microcephalic, was much more similar to LB1 than the current study found.
"That's what I don't quite understand," he said.
Falk said the two teams got different height measurements for the Basuto woman's skull, which in turn affected their analyses. Falk recently rechecked her team's measurements and believes they are accurate, she said.
Martin responded that his team's measurement technique is sound and he is confident that the Basuto woman's brain is similar to LB1.
He also questioned the Falk team's inclusion of juvenile microcephalics in their analysis. LB1 was an adult female.
Martin said hundreds of genes can produce a small brain, so "a proper comparison is with microcephalics that survive to adulthood."
According to Falk, age is irrelevant because microcephalic brains are fully developed by age ten. Her team wanted a diverse sample to "capture anything they might all have in common," she added.
Richard Potts, the director of the human origins program at the Smithsonian Institution in Washington, D.C., said that studies of brain shape alone will fail to resolve the debate between these research groups.
He said the scientists need to "step outside the black box of the brain they've gotten themselves into."
Although he declined to give specifics, Potts said forthcoming studies on other parts of the skeleton will "make for a compelling story that sides with the Falk camp."
Falk's study is "quite convincing the LB1 brain groups with the normal humans. It's a good example of that," Potts said.
"At the same time, there's no way I expect this to be the last word on the brain of LB1."
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