A fossil of a diminutive human nicknamed the “Hobbit” likely represents a previously unrecognized species of early humans, according to the results of a detailed comparison of the fossil’s brain case with those of humans, apes and other human ancestors.
Skeptics had argued that the Hobbit, discovered in Indonesia and first announced last fall, could have been an individual who suffered from a disorder known as microcephaly, which limits brain growth. The discoverers of the fossils had suggested that the Hobbit was either a pygmy form of a known species or a previously undiscovered species of early humans.
The new data on the Hobbit reveals little similarity to microcephalics and pygmies and supports the theory that the fossil is a member of a unique ancestral species, according to results published this week in the online edition of Science.
Scientists at the Washington University School of Medicine; Florida State University; the University of New England in Australia; and the Indonesian Centre for Archaeology, Jakarta, authored the new paper.
Australian and Indonesian archaeologists began to unearth the Hobbit in 2003 in a cave on the Indonesian island of Flores.
Tooth wear on the fossil, which appears likely to have been a female, indicated that she was a full-grown adult at the time of death. But she stood only about 3 feet tall and had a brain approximately one-third the size of modern adult humans.
Evidence suggests she may have lived as recently as 18,000 years ago.
The specimen came to be known as the Hobbit because her small size evoked the undersized protagonists known as Hobbits in J.R.R. Tolkien’s The Hobbit and The Lord of the Rings trilogy.
Based on similarities in exterior skull structure to humans and human ancestors, scientists suggested the Hobbit belonged in Homo, the genus classification that includes modern humanity.
Members of the genus are generically referred to as hominins. Scientists suggested naming the new species Homo floresiensis, after the island where the Hobbit was found.
Nothing remains of the Hobbit’s brain in her fossilized skull, but the living brain makes lasting impressions on the interior of the skull that can be used to infer some aspects of brain structure.
“We can analyze impressions inside the skull to suggest a positive — that a particular brain structure was there — but they can’t give us conclusive proof of a negative — that a brain structure was not there,” said study author Charles Hildebolt, Ph.D., associate professor of radiology at Washington University.
Lead author Dean Falk, Ph.D., the Hale G. Smith Professor and chair of anthropology at Florida State, is an expert in paleoneurology, the study of brain evolution.
Falk normally measures skull structure using calipers and dental floss. When the National Geographic Society supplied her with a cast of the Hobbit’s skull for analysis, Falk approached Hildebolt and other faculty members in WUSTL’s Mallinckrodt Institute of Radiology.
University radiologists, anthropologists and anatomists have developed several methods for using computed tomography (CT) and 3-D reconstruction to study human fossils. Using CT data that were obtained in Indonesia and advanced computer software, scientists produced a digital representation of the Hobbit’s brain case.
For comparison, scientists scanned brain cases in several skulls on loan from the Cleveland Museum of Natural History and the American Museum of Natural History.
As they did with the Hobbit data, scientists then used the scanning results to produce virtual endocasts — 3-D representations of likely features of the brains contained in the skulls.
Researchers produced additional data for comparisons by measuring latex endocasts, real models cast in latex of the likely brain structures found in 10 human skulls, 18 chimpanzee skulls and five skulls of Homo erectus, a hominin that lived in Asia and Africa about 2 million-25,000 years ago.
Included among the human skulls were a microcephalic skull and a pygmy skull. In microcephalic patients, chromosomal abnormalities impede normal growth of the top of the skull and the brain. Scientists found few structural similarities between the brains of modern microcephalics and the Hobbit.
“We still can’t rule out secondary microcephaly, which can be caused by exposure to infections or toxins in the womb,” Hildebolt said. “But there are reports that scientists in Indonesia have found more fossils like the Hobbit.
“As those surface, it becomes much harder to attribute their brain size to secondary microcephaly.”
Scientists also found little similarity to the Hobbit in the virtual endocast produced from the pygmy skull.
In addition to studying brain shapes, researchers conducted detailed comparisons of dimensions in the virtual endocasts.
These analyses identified several similarities between the Hobbit’s brain and that of Homo erectus.
However, there were also significant differences between the Hobbit and Homo erectus.
Falk identified a fissure near the back of the Hobbit’s brain as its lunate sulcus. The structure is similarly located toward the back of modern human brains.
“The lunate sulcus separates the primary visual cortex from the rest of the brain,” Hildebolt said. “It tends to get pushed toward the back of the brain as the occipital, parietal and temporal lobes expand, so normally it’s a sign of advanced brain development.”
The finding adds fuel to a debate about how advanced the Hobbit’s mental abilities may have been.
The cave where scientists found the Hobbit also contains remnants of stone tools, fire and a pygmy elephant, suggesting but not proving that Homo floresiensis may have had surprisingly advanced cognitive abilities, given its chimpanzee-sized brain.