Full Thread: Homo Floresiensis
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Old May 3rd, 2009 #3
Alex Linder
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[same story pg 2]

Excavations are continuing at Liang Bua, a wide-mouth cave in a hillside where the hobbit bones were found in deep sediments, but no more skulls or skeletons have turned up. Dr. Morwood said the search would be extended to other Flores sites and nearby islands.

Peter Brown, a paleontologist at the University of New England in Australia, said that his examination of the premolars and lower jaws of the specimens made it almost immediately “very, very clear that this was a hominid in the wrong place at the wrong time.” The first premolars in particular, he said, were larger than a human’s and had a crown and roots unlike those of H. sapiens or H. erectus.

Dr. Brown, a co-author of the original discovery report, said that no known disease or abnormality in humans could have “replicated this condition.”

At first, Dr. Brown and colleagues hypothesized that the hobbits were descendants of H. erectus that populated the region and had evolved their small stature because they lived in isolation on an island. Island dwarfing is a recognized phenomenon in which larger species diminish in size over time in response to limited resources.

The scientists soon backed off from that hypothesis. For one thing, dwarfing reduces stature, but not brain size. Moreover, researchers said, the hobbit bore little resemblance to an erectus.

In an analysis of the hobbit’s wrist bones, Matthew W. Tocheri of the Smithsonian Institution found that certain bones were wedge-shaped, similar to those in apes, and not squared-off, as in humans and Neanderthals. This suggested that its species diverged from the human lineage at least one million to two million years ago.

So if several lines of evidence now encourage agreement that H. floresiensis was a distinct and primitive hominid, the hobbit riddle can be compressed into a single question of far-reaching importance: where did these little people come from?

“Once you establish that this is a unique species,” said Frederick E. Grine, a paleoanthropologist at Stony Brook, “then these primitive features that it has suddenly take on a profound evolutionary significance.”

Scientists said in reports and interviews that they had only recently begun contemplating possible ancestries.

As a starting point, scientists rule out island dwarfing as a primary explanation. Dwarfs and pygmies are simply diminutive humans; they do not become more apelike, as the hobbits appear to be in some aspects. Besides, normal dwarfing would suggest that the hobbits presumably evolved from H. erectus, the only previous hominids identified in this part of Asia or anywhere outside Africa; the first one was discovered in Java in the late 19th century. But research has found few similarities between the hobbit skeleton and Asian H. erectus.

If the hobbit is a throwback to much earlier hominids, scientists said, reverse evolution would be the most far-fetched explanation. Dr. Jungers, a paleoanthropologist who organized the symposium, said there were no known examples of mammals becoming significantly reduced in size and anatomy as a consequence of reverting to an ancestral form.

“Is it possible?” he asked rhetorically. “If that is the case, it is unprecedented and a tremendous discovery.”

Several scientists think the answer to hobbit ancestry lies deeper in the hominid past. If this species is unlike H. erectus, it presumably descended from even earlier small-bodied migrants out of Africa that preceded erectus into Asia. Just the thought questions conventional wisdom.

Possible candidates include Homo habilis, the first and least known species of the Homo genus. The short, small-brained habilis might have emerged as early as 2.3 million years ago and lived to co-exist with the brainier, long-limbed H. erectus. At present, erectus fossils, found in the republic of Georgia and dated at 1.8 million to 1.7 million years ago, are the earliest well-established evidence for hominids outside Africa.

If hobbits resemble habilis in some respects, scientists said, it indicates that habilis or something like it possibly left Africa earlier and became the likely hobbit ancestor.

Another possible ancestor might even have been a pre-Homo species of the Australopithecus genus. The first evidence for stone toolmaking in Africa, at least 2.5 million years ago, is associated with australopithecines. Several scientists called attention to skeletal similarities between hobbits and A. afarensis, the species famously represented by the 3.2-million-year-old Lucy skeleton from Ethiopia.

The suggestion that the H. floresiensis ancestor might have reached Asia a million years before H. erectus left Africa was raised earlier this month at a meeting of the American Association of Physical Anthropologists.

And then there is the idea, raised again at the symposium, of hominid migrations out of Africa and back. Dr. Jungers advised abandoning the old image of the long-limbed H. erectus striding out of Africa in the first wave of hominids making their way in the world.

“Why think they couldn’t have done it many times, even before erectus?” he said. “Other mammals have migrated in and out of Africa.”

The idea revived speculation that erectus itself might have evolved in Asia from an earlier migrant from Africa, and then found its way back to the land of its ancestors. Similarly, other hominids arriving in distant parts of Asia might have churned out new species, among them the hobbits.

Robert B. Eckhardt of Penn State University, an ardent hobbit skeptic, is unyielding in his opposition to the interpretation that the Flores skull belongs to a previously unrecognized species. He insists that it will prove to be from a modern human stricken with microcephaly or a similar developmental disorder that shrinks the head and brain.

“Convincing others is much more difficult than I thought it would be at the outset,” Dr. Eckhardt acknowledged in an e-mail message, “but increasingly it is becoming evident that what is at stake is not just some sample of specimens, but instead the central paradigm of an entire subfield.”

Susan G. Larson, an anatomist at the Stony Brook School of Medicine who analyzed the non-human properties of the hobbit shoulders, said in an interview that the investigations had entered “a period of wait and see.”

“Someday,” Dr. Larson said, “people may be saying, why was everyone so puzzled back then — it’s plain to see where the little people of Flores came from.”