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."
end
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