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Inside the Head of the 'Hobbit'

Skull study boosts theory tiny fossil was distinct human species

THURSDAY, March 3, 2005 (HealthDay News) -- When she died 18,000 years ago on what is now the Indonesian island of Flores, the tiny 30-year-old female known only as LB1 had grown to what scientists believe was probably an average adult height for her kind: 3-feet, 4-inches.

And while her head and brain measured just a third of the size of modern humans, in the soil around her bones anthropologists found signs of intelligence and a primitive culture: artifacts such as charred animal bones, charcoal, and crude stone tools.

The unexpected discovery last fall of Homo Floresiensis -- quickly dubbed "hobbits" by Tolkien-loving anthropologists -- sent shock waves through the world of anthropology and evolutionary science.

While the paleoanthropologists who found LB1 put forth a theory that she represented a hitherto unknown strain of hobbit-sized human ancestors, others soon countered that she might simply be an ancient medical anomaly -- a microcephalic ("small-head") individual, her tiny head being the result of genetics or illness.

Research published in the March 4 issue of Science is helping put that theory to rest, however.

Detailed comparisons of the skulls of LB1, other hominins (human-like species) and chimpanzees strongly suggest Homo Floresiensis is not a random microcephalic, but instead a distinct -- and now extinct -- species.

"We had a skull of a true microcephalic, and the shape is nothing like what this LB1 fossil brain is shaped like," said study co-author Charles Hildebolt, a professor of radiology and anthropology at Washington University School of Medicine in St. Louis. He and his co-researchers -- who include the scientists who found LB1 -- now believe, more than ever, that Homo Floresiensis stands alone as a separate species.

Not everyone agrees. Andrew Kramer is an anthropologist at the University of Tennessee who specializes in Homo erectus, another hominin first unearthed in the Indonesian island of Java over a century ago. He was not involved in the Science study.

While Kramer said he never subscribed to the microcephalic theory, he said he leans more toward LB1 as being a dwarfed descendent of Homo erectus, not a unique species. "I always thought it looked an awful lot like erectus, at least the skull did," he said. "And with the [skull-cast] analysis provided in this study, it looks even more so."

In their study, Hildebolt and his colleagues conducted extensive detailed measurements of the LB1 skull, as well as skulls from today's Homo sapiens; a recent (now extinct) relative, Homo erectus; a human pygmy; a human microcephalic; and two much older ancestors of modern humans, Australopithecus africanus and Paranthropus aethiopicus.

Over a lifetime, the developing brain makes subtle impressions on the inside of the skull, so Hildebolt's team was able to use hi-tech technologies to produce virtual 3-D "endocasts" of what the brains of each of these specimens probably looked like.

"Similarities between the LB1 endocast and Homo erectus show a reorganization of the brain in a human direction, away from the ancestral apes, or australopithecine form of the brain," Kramer said.

The hobbit's brain was also quite distinct from those of microcephalic humans or pygmies, pulling the rug out from under that theory, the study authors said.

The clincher was something called the lunate sulcus -- a deep groove found in primate and human brains that separates large brain lobes. According to Hildebolt, in apes, the lunate sulcus occurs closer to the front of the skull, but in LB1 -- as in modern humans -- "it gets pushed backwards, to a more posterior position."

"Then there are the temporal lobes, lying on the sides of the brain. They are enlarged in LB1, similar to what you'd expect in a human brain," he said. "In [modern] humans, they're used to understand speech and hearing."

LB1's brain also appeared to be covered in deep, complex convolutions, another indicator of human-like brain development, Hildebolt said. "There's also an area right at the front of the frontal lobes, called Brodmann's Area 10," he added. "That area in humans is used for undertaking initiatives and planning future actions."

All of this points to heightened intelligence, and one big puzzle: How, experts wonder, could Homo Floresiensis be smart -- as these brain characteristics, and local signs of cooking and tools suggest -- and yet have a brain one-third the size of ours?

"That's why everyone is so startled and curious about this," Hildebolt said. "It really throws a monkey wrench into the gears, because from the standpoint of evolution, we've always thought that bigger brains are better."

"We have other questions, too -- how did Homo Floresiensis get to Flores -- by boat?" Hildebolt said. He pointed out that, even during the low-water mark of the last Ice Age, the island remained separated from other islands and the mainland by at least 12 miles of deep water.

Kramer contends that LB1 may not be a distinct species, however, but a diminutive descendent of Erectus. And he said it's still very possible that the burnt bones and rough tools found in the vicinity of LB1 "might have come from modern humans that came in and had a lot to do with Homo Floresiensis' eventual extirpation from the island."

Still, he said, if these artifacts do turn out to belong to the tiny-brained "hobbits," it could really shake up neuro-evolutionary theory.

"What this might be illustrating is that it isn't necessarily the size of the brain that's important [for intelligence], but rather the connections, the way the brain is put together," Kramer said.

No one knows exactly why Homo Floresiensis died off about 13,000 years ago. While they inhabited Flores, LB1 and her hobbit kind appeared to have hunted Stegadon, a now-extinct form of dwarf elephant. According to the team that found LB1, the area where she was found was littered with bones from smaller, juvenile Stegadons, more easily brought down by the tiny hobbit hunters.

In the meantime, rumors circulate that the team that found LB1 may have located more of her brethren.

"A lot of the argument behind the idea that this is some sort of 'pathological pygmy' is based on the fact that there's only one individual, one specimen," Kramer said. "If they find more stuff from the same layers that are obviously different individuals of Homo Floresiensis, then it's going to be really difficult to keep that argument alive."

More information

For a closer look at the human family tree, head to the Smithsonian Institution.

SOURCES: Charles Hildebolt, Ph.D., associate professor, radiology, and adjunct associate professor, anthropology, Washington University School of Medicine, St. Louis; Andrew Kramer, Ph.D., associate professor and head, department of anthropology, University of Tennessee, Knoxville; March 4, 2005, Science; photo courtesy of Washington University, St. Louis
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