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Ancient Remains Show Homo Sapiens had Company

By Pippa Wysong, Access Excellence

Armidale, Australia (01/20/05)- Its time for Homo erectus and Homo sapiens to move over and make room for a third member of the species who roamed the earth many thousands of years ago: Homo floresiensis. Discovered in September 2003 in eastern Indonesia, a series of skeletal remains found on the island of Flores show that this new, ancient relative had a diminutive stature, walked on two legs, and made tools. But one of the most impressive features is that H. floresiensis lived as recently as 18,000 years ago at a time when H. sapiens was also walking the earth.

The finding is so significant, the magazine Science, published by the American Academy for the Advancement of Science (AAAS), ranked it as one of the top ten research advances for the year 2004. Details of the initial discovery of a female skeleton were published in the journal Nature in October, 2004.

In the paper, researchers point out that it is widely accepted that during the Pleistocene era there was only one hominid genus (Homo). Until now it was thought there were only two species within the genus: H. erectus and H. sapiens. The bones found in Flores are sufficiently different from both H. erectus and H. sapiens that researchers have categorized it into a third and new species, H. floresiensis.

However, the researchers speculate that the new species may be descended from H. erectus which is known to have moved to Flores about 840,000 years ago. Animals that live on islands often become smaller in subsequent generations as an adaptive response to the environment. Where there is less space, less food available and no large predators, a small size is advantageous. It is not known how long it would have taken H. erectus to reach the more diminutive size of H. floresiensis.

"The location of these small hominins on Flores makes it far more likely that they are the end product of a long period of evolution on a comparatively small island, where environmental conditions placed small body size at a selective advantage," the Nature article states.

The first set of skeletal remains uncovered belonged to a female that was about 30 years of age when she died. Since then, remains from six other individuals have been found and all consistently showed hominins that were of short stature, with the adults being just over three feet tall (one meter). Stone tools were also found in the area.

The smaller body size was not due to any inherited defect, said Peter Brown (PhD), lead author of the study. "Different parts of the body grow at different rates. People with growth abnormalities usually have distinctive features in their skeletons. For instance, microencephalics have a very small brain case but a large and unusually shaped face on a normal body size," he said. Dr. Brown is from the University of New England in New South Wales, Australia. H. floresiensis did not have signs of these sorts of abnormalities, and the various sets of skeletal remains showed a consistent story.

H. floresiensis shared the island with Stegodon, a small type of elephant which they likely hunted. Over many generations "elephants get small on islands due to limited available calories to support large body size, therefore there are selective advantages in being small -- if there are no predators," Dr. Brown told Access Excellence. The small hominins lived on the island from about 38,000 years ago to about 18,000 years ago. During the Pleistocene Epoch the island was also home to giant tortoises, big rats, Komodo dragons and large lizards.

Several anatomical features make H. floresiensis a distinct species. "Body-size, brain-size, plus a combination of primitive and more advanced anatomical features are outside the range of all other known human relatives to hominins," Dr. Brown said.

The volume of the brain cavity, at 380cm2, is smaller than what is normally expected for the genus Homo. Yet there were stone tools found in the area, adding new questions about brain size and the ability to create and use tools. The small brain size, in addition to the shape of the hip-bone might favor classification as an australopithecine -- a much older, chimpanzee-like ancestor, the researchers said. However, the size and shape of the skull of H. floresiensis suggests a primitive form of H. erectus.

In an interview printed in Nature, Dr. Brown added: "H. floresiensis was not likely to have contributed to the gene pool of Homo sapiens. Its importance is not in the evolutionary story of modern humans, but in how the broad group from which modern humans evolved may have adapted and evolved to different ecosystems. Prior to this finding it would not have been thought that a hominin with the brain size, and possibly limited cognitive ability, of H. floresiensis could make the type of tools associated with the skeleton, or even get to Flores at all."

An accompanying editorial, by Chris Stringer, a palaeontologist at the Natural History Museum in London, adds that "modern humans must surely have encountered this tiny relative of ours, and the discovery shows how much we still have to learn about the story of human evolution."


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