"Hobbits" May Have Been Genetic Mutants
for National Geographic News
|January 3, 2008|
A rare disease characterized by small brain and body size but near normal intelligence is caused by mutations in a gene coding for the protein pericentrin, researchers have found.
The scientists speculate that the condition may explain the tiny, hobbitlike people that occupied a remote, Indonesian island about 18,000 years ago—adding fuel to the debate over whether the unusual creatures were a new species or just diseased modern humans.
Pericentrin helps separate chromosomes during cell division, which is needed for growth.
"The whole body loses its capacity to grow, because cell division is so difficult for people with this defect," said study co-author Anita Rauch of the Institute for Human Genetics at the University of Erlangen in Germany.
On average, disease sufferers grow about three feet (a meter) tall and have a brain the size of a three-month-old baby. However, their intelligence is near normal.
People with the defect also exhibit subtle bony anomalies in their hands and wrists, skull asymmetry, small chins, abnormal teeth, and abnormal shoulders, Rauch said.
Descriptions of the hobbitlike people match those of modern humans with this genetic defect, Rauch added.
When the hobbit was discovered in 2004 on the Indonesian island of Flores, scientists hailed it as a new species: Homo floresiensis.
Since then, scientists have debated whether the hobbit is indeed a new species or a modern human with a genetic disease that causes small brains called microcephaly.
The new study links the genetic mutations to a type of microcephaly that limits all growth—that of the brain and the body.
"We think it is very likely that Homo floresiensis indeed had a pericentrin mutation," Rauch said.
She added that, on islands like Flores, inherited diseases become commonplace because of the higher levels of mating among closely related people.
The finding is reported online today in the journal Science.
Down to the Details
Richard Potts, director of the human origins program at the Smithsonian Institution in Washington, D.C., closely monitors the scientific debate over Homo floresiensis.
He said the new study's link between genetics and human growth is "neat" but disagreed with the suggestion that Homo floresiensis represents a modern human with a genetic disorder.
Proof that the hobbit is indeed a unique species, he said, is found in recent detailed studies of its wrist and upper arm bone.
A wrist bone study published in Science last September found that the hobbit's wrist bones were primitive, like those in gorillas or chimpanzees.
No known genetic diseases, including any type of microcephaly, results in an apelike wrist similar to the hobbit's, the authors of the wrist bone study concluded.
"For many of us in the field, we have taken those studies, especially the one [on the wrist bone] as really being the death blow to the idea that we're dealing with a modern human," Potts said.
And even if the researchers find a gene in the hobbits connected with dwarfism in modern humans, they would "still have to go down to the details of the morphology and try to explain [them]," he added.
Dean Falk is an anthropologist at Florida State University in Tallahassee who has led several studies demonstrating Homo floresiensis is a unique species, not a diseased modern human.
She commented via email that the new study is unconvincing—for one, the pictures shown of people with this defect look nothing like the hobbit.
"Their heads are too large relative to their bodies, the limb proportions are all wrong, the profiles of the face do not come close, and these individuals are from 8 to 12 years old," she wrote.
The hobbit fossil, known as LB1, is from an individual about 30 years old.
Study co-author Rauch and her colleagues, meanwhile, hope that improved technology may soon allow them to extract DNA from the Flores fossils and test it for mutations to the pericentrin gene.
The new research, Rauch noted, demonstrates that a single genetic defect can lead to miniaturization and distinct bone shape in humans.
Rauch also plans to investigate connections between pericentrin mutations and natural variation in the modern human population.
She said that there are a lot of small changes in the gene between normal people—not enough to cause dwarfism but sufficient to make one person smaller than another, for example.
"If you don't have the full mutation which leads to absence [of the protein]," she said, "but only a little change, this might cause little differences in the normal population."
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