The three-foot human "flores hobbit" who lived on the Indonesian island of Flores more than 13,000 years ago had a sophisticated brain which was rewired internally to compensate for its small size, a study has found.
An internal cast of the brain case shows that the hobbit possessed rare cranial features that would probably have conferred unusual intelligence on such a small creature, scientists said.
The findings pour cold water on the idea that the hobbit was not a new species of human but an ordinary person suffering from microcephaly, a disease that causes stunted growth and small brain size.
Ever since scientists announced in 2004 that they had discovered the skull and partial skeleton of a tiny human female on Flores, experts have argued about whether she belonged to new species of human or was just someone born with microcephaly.
The latest study confirms beyond any reasonable doubt that the Flores skull belongs to a new species who was probably intelligent enough to make and use the tiny stone tools found alongside the bones, said Professor Dean Falk of Florida State University in Tallahassee. "It's as definitive as it can be. We feel that we've answered the questions raised by the people who contend that the hobbit is a microcephalic," Professor Falk said. "People refused to believe that someone with a brain that small could make the tools. How could it be a sophisticated new species?"
The volume of the hobbit's brain is only 417 cubic centimetres, about a third of the size of a normal adult. Some scientists said that such a small brain would not be able to carry out the tasks of tool making and tool using associated with being human.
However, a team of scientists led by Professor Falk compared the internal cast of the hobbit's braincase with similar "endocasts" of 10 normal, healthy people and nine people with microcephaly.
A computer reconstruction of her brain, and measurements of its internal dimensions, placed it clearly within the normal range of brains and not within the range of microcephalics, Professor Falk said.
The scientists also found that the brain case has four unusual features - which left endocast impressions - that distinguishes it from the brain cases of Homo sapiens. These features, they argue, justify its classification as a separate species, named Homo floresiensis.
"It has a combination of features that I've not seen before in any other primate endocasts. They had a little brain that had been globally reorganised and which didn't get bigger - it got more complex. It got rewired and reorganised and that's very interesting," Professor Falk said.
Other scientists had previously criticised Professor Falk and her colleagues for a similar study which relied heavily on the endocast of just one microcephalic.
However, this time the study, published in the journal Proceedings of the National Academy of Sciences, used nine endocasts of microcephalics ranging in age and ethnicity to counter suggestions of biased data.
"We feel that we've answered the criticisms. If people still want to insist that the hobbit is a microcephalic, then they must bring us a microcephalic skull that looks like the hobbit," Professor Falk said.
Dating suggests that the hobbit lived on Flores for many tens of thousands of years and probably died out about 13,000 years ago following a massive volcanic eruption. If so, it would mean that a diminutive species of human being was living alongside "ordinary" humans at a time when it was thought that we were the only ones on Earth.