The diminutive people were similar in size to the so-called hobbit discovered in National Geographic Society-supported excavations on the Indonesian island of Flores in 2003.
Scientists classified the hobbit as a separate human species, Homo floresiensis.
According to Berger, the estimated brain size of the early Palauans is about twice the size of the hobbit brain.
Several other features, including the shape of the face and hips, suggest that the Palauan bones should be classified as Homo sapiens.
If the interpretation of the Palauan remains is correct, the find may add more fuel to the debate over whether the Flores hobbit is a unique species, Berger said.
Aside from being tiny, the Palauan bones show that some of these people lacked chins and had deep jaws, large teeth, and small eye sockets, according to the paper.
Some of these features were considered important in originally distinguishing the hobbit as a unique—and archaic—species, Berger said.
But the Palauan remains suggest these features may just be a consequence of insular dwarfism, a shrinking process that some scientists attribute to the stresses of a small island environment.
Palau lacks indigenous terrestrial mammals and large reptiles that early Palauans might have used for food.
Archaeological records indicate fishing was not a local activity until about 1,700 years ago, around the time bigger bones appear in the caves.
The early Palauans' limited diet, combined with a tropical climate, absence of predators, a small founding population, and genetic isolation, may have produced "these very odd features and very small body size," Berger said.
William Jungers, an anthropologist at Stony Brook University in New York and a former National Geographic grantee, stands by his conclusion that the hobbit is a unique species.
He notes that the small bones, large teeth, lack of a chin, and other features that characterize the early Palauans as well as the hobbits can be found in other small-bodied human populations around the world.
But "the smallest-bodied people on Earth do not converge on the proportions and various aspects of morphology of the hobbits," Jungers said.
Jungers points out that the hobbit is distinguished from modern humans by jaw structures called transverse tori, which are seen in human ancestors, such as australopithecines and some Homo erectus fossils, he noted.
Chris Stringer, lead researcher in the human-origins program at London's Natural History Museum, points to other defining characteristics in the hobbits' feet, teeth, and shoulder and wrist bones.
Based on this evidence, he says, "I still believe that the Flores material is something distinct and primitive."
Berger says his team has yet to analyze the shoulder, feet, and wrist bones in their Palauan sample and thus cannot comment on how they compare to the hobbit bones.
A Disease Factor?
Unlike the Palauan bones, the hobbit fossils include a skull with an exceptionally small braincase. Its volume is much smaller than that of small-bodied peoples living today on other Pacific islands and in the forests of Africa. It is also smaller than that of the early Palauans.
Some scientists argue that the unusually small brain volume of the hobbit makes it not a unique species but rather a small-bodied Homo sapiens with microcephaly, a genetic disease that causes small brains and other abnormalities.
(Read related story: "'Hobbit' Humans Were Diseased, Not New Species, Study Says" [May 18, 2006].)
A team of researchers from Australia recently reported that the unusual limbs of Homo floresiensis may also have been influenced by disease.
The distortions, they claim, are sometimes seen in the offspring of a normal, small-bodied human female with goiter.
Berger says his team's findings might support these disease arguments. But they have yet to find an individual in their sample who had one of these diseases and therefore can't make a comparison.
The Debate Continues
Dean Falk is an anthropologist at Florida State University in Tallahassee who received National Geographic funding to compare the Flores skull with both microcephalics and modern humans without disease.
She and colleagues from the Mallinckrodt Institute of Radiology concluded in a study published last year that the hobbit was not microcephalic.
Falk said the finding closed the microcephaly argument. The Palauan remains, she added, are just a set of small bones, representing small-bodied people.
""But being small does not make one comparable to Homo floresiensis," she noted. "It makes one small—period."
Steven Churchill, a paleontologist at Duke University and co-author of the new study, says the Palauan discovery expands the known range of variation in modern humans in Southeast Asia, adding context in which to interpret the hobbit fossils.
Several scientists, he adds, continue to believe "there's something wrong with Flores."
One of these scientists is Robert Martin, the curator of biological anthropology at the Field Museum in Chicago, Illinois.
He says it's well known that small-bodied human populations exist in Southeast Asia.
A community of pygmies now lives near the Flores hobbit site in the village of Rampapasa, so finding small-bodiedHomo sapiens on Palau, he says, "is no surprise."
From Martin's perspective, the problem with the classification of the hobbit as a separate species is that it is based largely on the brain size of "one microcephalic individual in Flores. Body size is really a separate issue."
According to Berger, the new findings suggest that "you don't have to look very far to find the facial and dental characters thought to be unique in Flores."
If traits such as those found among the early Palauans are common on islands, he said, then scientists who want to name a new species in the human lineage will have to present "a much better case built on a lot more fossils before the world will buy it."
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