Some scientists have speculated that the hobbit fossil was not of a new species but rather of a modern human with microcephaly, a birth defect in which a person has an abnormally small brain. To address this concern, Falk's team also compared the hobbit braincase to that of a known modern human microcephalic.
"We think it least resembles a microcephalic," Hildebolt said. "It has a lateral profile that is somewhat similar to a Homo erectus, but it has other features that are similar to modern humans. The combination is unique."
Falk agrees and contends that the exhaustive analysis puts skeptics' claims that the hobbit is really a microcephalic to rest.
"The scaling of brain to body isn't at all what we'd expect to find in Pygmies, and the shape is all wrong to be a microcephalic," Falk said. "This is something new."
Although much smaller than in modern humans, the hobbit's frontal lobe contains a region known as Brodmann's area 10, which is very convoluted and has large swellings. In the modern human brain, area 10 is associated with higher cognitive processes such as planning ahead and taking initiative.
When scaled for size, the hobbit also has larger temporal lobes than Homo erectus does. In modern humans the temporal lobes are associated with hearing and understanding speech.
"This species was undergoing its own long evolution on this island," Falk said. "Our data are consistent with the kinds of sophisticated behaviors being reported."
H. floresiensis "is a really strange combination of some very advanced traits, some that are very primitive, and some that are unique," said Mike Morwood, an archaeologist from the University of New England in Australia. Morwood led the team that first found the hobbit remains.
Morwood said the stone tools found close to the H. floresiensis fossils represent "a very sophisticated assemblage of stone artifacts and are directly associated with evidence of hunting and butchering of stegadon, a dwarf elephant."
Hildebolt, though, pointed out that this doesn't automatically mean that the tools and cooking evidence are associated with the new species. Other scientists agree with him.
"I am cautious about drawing too many conclusions about brain quality from endocranial surface features [features inside the skull], and I am still cautious about the extent of the 'advanced' behavior inferred for Homo floresiensis from the archaeological evidence," said Chris Stringer, director of the Human Origins Program at the Natural History Museum in London.
"For me, the most significant aspects of this new study are the demonstration that the endocranium is very different from that of a small-bodied, or a microcephalic, H. sapiens and that it does, with some differences, most resemble endocasts of H. erectus."
The Falk team's report appears in today's issue of the online version of the journal Science. Their findings will also be featured on the National Geographic Channel's Explorer TV series on March 13 at 8 p.m. ET/PT.
Tiny Contemporary Humans?
Scientists have long thought that, with the extinction of the Neandertals roughly 30,000 years ago, H. sapiens was the only human species left on the planet. The discovery that another human species, vastly different from us, existed up until about 13,000 years ago is a stunning find.
Who were they and how did they get to Flores? There are several hypotheses.
The team of archaeologists that found the hobbit fossilsled by Mike Morwood, Bert Roberts, and Thomas Sutiknasuggested that the hobbits' small stature was the result of a phenomenon known as island dwarfing.
Flores island has been inhabited by some species of human since at least 800,000 years ago. The team that found the fossils leans toward the theory that, once there, this earlier species evolved into H. floresiensis.
Over thousands of years, the theory goes, their bodies adapted to the constraints of island living in the same way that many other mammals' bodies do. With food in short supply, their skeletons grew smallera process called island dwarfing.
And because reptiles on islands frequently grow larger, the hobbits may have been both predators and prey. If so, they would have needed to be smarter just to survivethere would be a significant evolutionary advantage to developing a more highly evolved brain.
"Small and smart is definitely better than small and dumb," Hildebolt laughed.
The authors of the braincase study, which was funded by the National Geographic Society, support an alternative hypothesis that was originally presented by the team that found the fossils.
They suggest that H. floresiensis existed as a species before arriving on Floresthat it was already tiny on arrival. It's possible, they say, that there was a small-bodied, small-brained, as yet unknown species of human ancestor (possibly H. floresiensis) that may have left Africa at around the same time as Homo erectus, about 1.8 million years ago.
"We're not dismissing the island-dwarfing hypothesis. It's just that we think the other seems maybe a little stronger," Hildebolt said.
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