St. Louis Post-Dispatch

ST. LOUIS – When it comes to brains, shape, not size, is what really counts.

That’s one of the lessons researchers are learning from the analysis of a tiny 18,000-year-old human cousin from Indonesia.

Last year, a team of Australian and Indonesian researchers reported the discovery of fossils from a diminutive hominid on the island of Flores. The scientists named the creature Homo floresiensis. But the three-foot tall female fossil (cataloged as LB1) is better known by the nickname “Hobbit.”

Hobbit had a tiny brain, about the size of a grapefruit, said Charles Hildebolt, an anthropologist at the Mallinckrodt Institute of Radiology at Washington University. The Hobbit’s remains were associated with sophisticated stone tools and charred animal bones, indicating that the creatures could have hunted pygmy elephants and cooked food. Those capabilities were previously thought to be impossible for a primate with such a small brain, he said.

“If this little creature actually was using the fire and making the tools, that tips human evolution up-side-down, or at least confuses it,” Hildebolt said.

Hildebolt and his colleague Kirk Smith teamed with Florida State University anthropologist Dean Falk to decipher the Hobbit’s brain structure. The researchers used data from CT scans of Hobbit’s skull made in Indonesia to construct models of the brain. Such models, called endocasts, capture the impressions that living, pulsating brains make inside the skull, Falk said.

“I started out a skeptic. I thought we were going to see a little chimpanzee-type brain,” Falk said. Instead the researchers found a brain with a complex mixture of primitive and advanced characteristics, some akin to structures associated with intelligence in humans.

“I’m bowled over. Never thought I would see it in a brain this small,” Falk said.

The study was published Thursday in Science Express, the online version of the journal Science.

The team rejected the theory that Hobbit was actually a modern human with a genetic condition called microcephaly, which causes the brain case to shrink. The scientists compared LB1’s brain with one from a person with “true” microcephaly – called Microcephalia vera – and found that the two looked nothing alike.

And the little hominid probably wasn’t a pygmy human either. Human children and adult pygmies and dwarves have large heads in comparison to the rest of the body, Hildebolt said. Hobbit’s head was small in proportion to its body, much like Australopithecus – another human ancestor made famous by the fossil called Lucy.

But other scientists aren’t willing to give up on the idea that some type of genetic disorder may have caused Homo floresiensis’s head and brain to shrink.

“The choice of one single microcephalic specimen from Europe does not make the case for getting rid of the pathology hypothesis,” said Ralph Holloway, a paleoneurologist at Columbia University. Other types of brain-shrinking disorders, such as nannocephaly (“bird-headed dwarfism”), may produce a brain like Hobbit’s, he said.

The fossil’s co-discoverers previously postulated that Hobbit may have been a dwarf Homo erectus, a human ancestor that lived in Indonesia about the same time.

The new study indicates that Homo floresiensis’s overall brain shape was similar to Homo erectus, but at 417 cubic centimeters was about a third the size of Homo erectus. And Hobbit had brain structures never before found in Homo erectus, but which are characteristic of modern human brains, Falk said.

Hobbit had “fat” temporal lobes – structures that in living humans are specialized for hearing, speech processing, memory, emotions and identifying and naming people, animals and objects, Falk said. And LB1 had large frontal lobes, including a “whopping big swelling” right where humans have Brodmann’s area 10, a part of the brain involved in planning and initiative, she said. At the back of the brain, a furrow called the lunate sulcus was positioned in a location reminiscent of human brains.

Holloway has long been an advocate of the notion that rearranging the brain rather than simply making it bigger could contribute to intelligence. But even he finds the idea that Homo floresiensis with its minuscule brain was capable of advanced thinking hard to swallow.

“It’s just that 417 cc’s is exceedingly small. And if it’s not (due to) pathology and they did indeed make these stone tools, then we’d have to abandon all of our ideas about how brain size and structure influence behavior … or at least rethink them,” Holloway said.