Mei 到處 8

http://www.abc.net.au/news/stories/2009/05/07/2562944.htm

Ancient 'hobbits' a new species after all

Posted Thu May 7, 2009 6:40am AEST
Updated Thu May 7, 2009 12:52pm AEST

New species: A 'hobbit' skull (REUTERS)

• Video: Ancient 'hobbits' a new species after all (ABC News)
• Audio: Studies from head to toe show Indonesian 'hobbit' is a new type of human (AM)

Diminutive humans whose remains were found on the remote Indonesian island of Flores in 2003 truly are a new species, and not pygmies whose brains had shrivelled with disease, researchers say.

Anthropologists have been arguing about the identity and origins of Homo floresiensis - dubbed "the hobbit" due to its small size - since it was unearthed by an Australian-led research team.

Measuring about a metre tall and weighing in at 30 kilograms, the tiny, tool-making hunters may have roamed the island for which they were named as recently as 8,000 years ago. The fossils are about 18,000 years old.

Many scientists have said H. floresiensis were prehistoric humans descended from Homo erectus, stunted by natural selection over millennia through a process called insular dwarfing.

Others countered that even this evolutionary shrinking, well known in island-bound animals, could not account for the hobbit's chimp-sized grey matter of barely more than 400 cubic centimetres, a third the size of a modern human brain.

And how could such a being have been smart enough to craft its own stone tools?

The only plausible explanation, they insisted, was that the handful of specimens found suffered from a genetic disorder resulting in an abnormally small skull or - a more recent finding - that they suffered from "dwarf cretinism" caused by deficient thyroids.

Two new studies in the British journal Nature go a long way toward settling this debate, even as they raise new quandaries that are sure to stoke further controversy.

A team led by William Jungers of the Stony Brook University in New York tackled the problem from the other end by analysing the hobbit's foot.

In some ways it is very human. The big toe is aligned with the others and the joints make it possible to extend the toes as the body's full weight falls on the foot, attributes not found in great apes.

But, in other respects, it is startlingly primitive: far longer than its modern human equivalent, and equipped with a very small big toe, long, curved lateral toes, and a weight-bearing structure closer to a chimpanzee's.

Recent archeological evidence from Kenya shows that the modern foot evolved more than 1.5 million years ago, most likely in Homo erectus.

So unless the Flores hobbits became more primitive over time - a more-than-unlikely scenario - they must have branched off the human line at an even earlier date.

For Dr Jungers and colleagues, this suggests "that the ancestor of H floresiensis was not Homo erectus but instead some other, more primitive, hominin whose dispersal into southeast Asia is still undocumented," the researchers conclude.

Companion studies, published online in the Journal of Human Evolution, bolster this theory by looking at other parts of the anatomy, and conjecture that these more ancient forebear may be the still poorly understood Homo habilis.

Either way, their status as a separate species would be confirmed.

Even this compelling new evidence, however, does not explain the hobbit's inordinately small brain.

That's where hippos come into the picture.

Eleanor Weston and Adrian Lister of the Natural History Museum in London compared fossils of several species of ancient hippos found on the island of Madagascar with the mainland ancestors from which they had evolved.

They were surprised to find that insular dwarfing - driven by the need to adapt to an island environment - shrank their brains far more than had previously been thought possible.

"Whatever the explanation for the tiny brain of H floresiensis relative to its body size, our evidence suggests that insular dwarfing could have played a role in its evolution," they conclude.

While the new studies answer some questions, they also raise new ones sure to spark fresh debate, notes Harvard professor Daniel Lieberman in a comment, also published in Nature.

Only more fossil evidence will tell us whether the hobbits of Flores evolved from Homo erectus, whose traces have been found throughout Eurasia, or from an even more ancient lineage whose footsteps have not yet been traced outside Africa, he said.

In either case, however, it now seems unlikely that they were cretins, in any sense of the word.

-AFP/ABC