By JOSEPH B. VERRENGIA, AP Science Writer
Scientists say they have found more bones in an Indonesian cave that offer additional evidence of a second human species — short and hobbit-like — that roamed the Earth the same time as modern man.
But the vocal scientific minority that has challenged that conclusion since the discovery of Homo floresiensis was announced last year remains unconvinced.
The discovery of a jaw bone, to be reported in Thursday's issue of the journal Nature, represents the ninth individual belonging to a group believed to have lived as recently as 12,000 years ago. The bones are in a wet cave on the island of Flores in the eastern limb of the Indonesian archipelago, near Australia.
In 2004, scientists announced their original, sensational discovery of a delicate skull and partial skeleton of a female, nicknamed "Hobbit" and believed to be 18,000 years old. In addition, they found separate bones and fragments of other individuals ranging in age from 12,000 to 95,000 years old.
The findings have ignited a controversy unlike any other in the often-contentious study of human origins.
The tiny bones have enchanted many anthropologists who accept the interpretation that these diminutive skeletons belonged to a remnant population of prehistoric humans that were marooned on Flores with dwarf elephants and other miniaturized animals, giving the discovery a kind of fairy tale quality.
If true, the discovery grafts a strange and tangled evolutionary branch near the very top of the human family tree.
The conventional view of human evolution is that several types of primitive ape-like ancestors appeared and faded over a span of about 4.5 million years. Modern Homo sapiens developed about 100,000 years ago, and quickly overtook other large-brained competitors like Homo erectus and Neanderthals. Modern humans were thought to have roamed the Earth without competition for at least the past 30,000 years.
Fully grown, Homo floresiensis would have stood about 3 feet tall, with a brain about the size of a chimpanzee.
Its discoverers, led by Australian anthropologist Michael Morwood of the University of New England, speculate it evolved from Homo erectus, which had spread from Africa across Asia. They attribute its small size to its isolation on an island.
However, the researchers acknowledge that the Hobbit shares a bizarre and unexplained mixture of modern and primitive traits. For example, its long, dangling arms were thought to have belonged only to much older prehuman species that were confined to Africa.
A vocal scientific minority insists the Hobbit specimens do not represent a new species at all. They believe the specimens are nothing more than the bones of modern humans that suffered from microencephaly, a broadly defined genetic disorder that results in small brain size and other defects.
And, at least two groups of opponents have submitted their own studies to other leading scientific journals refuting the Flores work.
"This paper doesn't clinch it. I feel strongly that people are glossing over the problems with this interpretation," said Robert Martin, a biological anthropologist and provost of the Field Museum of Natural History in Chicago.
Those caught in the middle of the debate say it is a real test of what we know about human evolution.
Daniel E. Lieberman of the Peabody Museum at Harvard said the specimens are so unusual that they deserve a more detailed analysis in order to adequately answer the critics' complaints.
"Many syndromes can cause microencephaly and dwarfism and they all need to be considered," said Lieberman, who wrote a commentary in Nature. "The findings are not only astonishing, but also exciting because of the questions they raise."
In the latest Nature study, the same team of Australian and Indonesian scientists working in Liang Bua cave on Flores report finding a variety of additional bones buried at various depths.
Among them, bones from the right arm of the previously discovered 18,000-year old female. They labeled her LB1.
And, they report finding the lower jaw bone that does not belong to any of the previously discovered individuals. An analysis of firepit charcoal found nearby in the excavation layer suggests the jawbone is 15,000 years old. It suggests a weaker chin with smaller tooth dimensions than LB1, but otherwise shares the same characteristics.
"They almost certainly belong to the same species," Lieberman concluded.
By JOSEPH B. VERRENGIA, AP Science Writer