May 6, 2009

Research Suggests ‘Hobbits’ Are Indeed A New Species

Two studies reported on Wednesday argue that the 18,000-year-old fossil remains of tiny humans found in 2003 in the remote Indonesian island of Flores are indeed a new species, and not pygmies whose brains had withered with disease.

Anthropologists have bitterly debated the identity and origins of these cave-dwelling relatives since the discovery of Homo floresiensis "“ often referred to as "the hobbit" due to its small size.

Measuring roughly 3 feet tall and weighing 65 pounds, the diminutive, tool-making hunters may have lived as recently as 8,000 years ago. 

Many scientists have argued that H. floresiensis were prehistoric humans descended from Homo erectus that became stunted by natural selection over the ages by a process called insular dwarfing.

Others maintained that even this evolutionary shrinking, notorious in island-bound animals, could not account for the hobbit's chimp-sized grey matter of roughly one-third the size of a modern human brain.

With such small brains, how could they have been smart enough to build their own tools?

The scientists argued that the only plausible explanation was that the handful of specimens discovered had suffered from a genetic disorder resulting in an unusually small skull, or they had perhaps suffered from "dwarf cretinism" caused by deficient thyroids.

Although the two new studies go a long way towards ending the debate, they also raise new questions that will surely invoke further controversy.

A team led by William Jungers of the Stony Brook University in New York tackled the debate from the other end, by studying the hobbits' foot, which in some ways looks very human.  The big toe is aligned with the others, and the joints allowed the hobbits to extend their toes as their body's full weight fell on the foot. Neither attribute is found in great apes.

However, in other respects the hobbits is remarkably primitive.  For instance, the foot is far longer than its modern human equivalent, and consists of a tiny big toe, with long, curved lateral toes and a weight-bearing structure resembling that of a chimpanzee's.

According to recent archeological evidence from Kenya, the modern foot evolved more than 1.5 million years ago, most likely in H. erectus.  Therefore, unless the Flores hobbits became more primitive over time -- a highly unlikely scenario -- they must have diverged from the human line at an even earlier point in time.

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," concluded Jungers and his colleagues.

Companion studies that examined other parts of the hobbits' anatomy support this theory and other speculation that the ancient forebear may be the much-understood Homo habilis.

However, the hobbits' status as a separate species would be confirmed either way.

Nevertheless, the compelling new evidence does not explain the hobbit's unusually small brain.  That's where hippos may be able to help.

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

Surprisingly, the researchers found that insular dwarfing -- driven by adaptation to an island environment -- shank their brains far more than had previously believed 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," Lister and Weston concluded.

In a commentary on the studies, Harvard professor Daniel Lieberman wrote that while the new research answers some questions, they also spark new issues for debate. Only additional fossil evidence will confirm whether the hobbits of Flores evolved from H. erectus, who roamed throughout Eurasia, or from an even more ancient lineage whose footsteps have not yet been traced outside Africa, Lieberman said.

Either way, it seems unlikely that they were cretins, he said.

The two new studies were published in the British journal Nature, while companion studies were published online in the Journal of Human Evolution.


Image Caption: A cast of a Homo floresiensis skull, American Museum of Natural History. Image Courtesy Ryan Somma - Wikipedia


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