It's not the size of the brain that matters. It's the way it's arranged. That's the conclusion of researchers studying the skull of a tiny, Hobbit-like human ancestor who lived on a remote Indonesian island 18,000 years ago.
Researchers are reporting today that the grapefruit-size brain had sophisticated characteristics found only in modern humans. They said the findings offer further evidence that the tiny hunter discovered last year was a unique archaic species that coexisted with modern humans long after other primitive ancestors died out.
Thomas Sutikna of Indonesia's center for archaeology holds the fossil of a human ancestor that has been nicknamed Hobbit for its diminutive size.
(Ira Block -- National Geographic Via AP)
"It's remarkable," said Florida State University paleoneurologist Dean Falk, leader of the team that studied the skull. "I thought we were going to be looking at a chimpanzee skull, but this has advanced features that I've not seen in anything this size."
Falk's study, published in the journal Science, was conducted at the behest of the National Geographic Society and with the collaboration of the Australian-led team that found the fossil. The new research, however, failed to still skeptics who have dismissed the finding as a pygmylike modern human, or a modern human with a deformity known as microcephaly -- a small head and brain.
The tools and artifacts found with the skull "were made by [fully competent] modern humans," said paleoanthropologist James Phillips of the University of Illinois and Chicago's Field Museum in a phone interview. "This individual could not mentally have made them."
The fossil was discovered in a limestone cave on Indonesia's Flores Island. It lies immediately east of the "Wallace Line," which divides islands that once were connected to Australia and Asia and those, such as Flores, that remained isolated for millions of years.
The team, led by Michael J. Morwood of Australia's University of New England, estimated the fossil was 18,000 years old, meaning it had survived long after modern humans appeared 150,000 years ago and well after the extinction 30,000 years ago of Neanderthals, the last known archaic human.
The team suggested that the fossil exemplified the "island rule": that isolated islands with limited resources and no natural predators cause large animals to get smaller, while small animals get larger. Prehistoric Flores had miniature elephants and giant Komodo dragons.
The team found remains of seven tiny people, including the nearly complete skull of a 30-year-old woman. They dubbed the fossils Homo floresiensis, which quickly acquired the nickname Hobbit after the diminutive characters in author J.R.R. Tolkien's fantasies.
What astounded anthropologists, however, were the sophisticated stone points and barbs found with the remains. Evolutionary orthodoxy holds that advances in human skills -- such as tool-making -- come with increases in brain size, and such weapons had never appeared before the advent of modern humans.
The Hobbit, by contrast, had a 25 cubic-inch brain -- comparable to primitive human ancestors who lived 2.5 million to 3 million years ago. "It was shocking," said Rick Potts, director of the Smithsonian Institution's Human Origins Program, in a telephone interview. "When you thought about it, you realized that [island adaptation] had happened to other mammals, but I was a doubter."
Falk, working with colleagues at Washington University's medical center, in St. Louis, and the Australian discovery team, made "endocasts" of the inside of the fossil skull and built electronic and plastic mock-ups of the brain. Then her team compared them with those of modern humans, chimpanzees, a human ancestor common in Indonesia and a microcephalic individual from Europe.
Falk found that the brain's general shape most closely resembled the human ancestor, Homo erectus, albeit much smaller. But she also found outsize temporal lobes along its sides -- a characteristic of modern humans.
The Hobbit's frontal lobe was also highly convoluted, another characteristic of modern humans. All this "just blew me away," Falk said in a telephone interview. "The message is that it's its own creature with a suite of features that are unique."
The tests showed that the fossil had little in common with the microcephalic specimen, but Field Museum primatologist Robert Martin, a leading skeptic, said testing against a single sample proved nothing. "They don't even tell you if [the microcephalic] was an adult," Martin said in a phone interview. "I'm suggesting the Flores discovery is a pathology, and I'm surprised they would publish this with such limited information."
Falk said that the microcephalic skull "was typical . . . and we are confident that [the Hobbit skull] is not a true microcephalic."