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Thursday, April 22, 2010

Hobbit debate goes out on some limbs

Hobbit debate goes out on some limbs
Arm and leg fossils may, or may not, come from nonhuman hominid
By Bruce Bower
Web edition : Monday, April 19th, 2010


ALBUQUERQUE — Two fossil hobbits have given what’s left of their arms
and legs to science. That wasn’t enough, though, to quell debate over
hobbits’ evolutionary status at the annual meeting of the American
Association of Physical Anthropologists on April 17.


Since 2004, the discoverers of unusual “hobbit” fossils on the
Indonesian island of Flores have attributed their find to a pint-sized
species, Homo floresiensis, that lived there from 95,000 to 17,000
years ago. These researchers also suspect, on the basis of hobbit
anatomy and recent stone tool discoveries on Flores, that H.
floresiensis evolved from a currently unknown hominid species that
migrated from Africa to Indonesia more than 1 million years ago.


Critics say the finds represent nothing more than human pygmies like
those still living on Flores. In their opinion, the centerpiece hobbit
find — a partial skeleton of an adult female known as LB1 — is what’s
left of a woman who suffered from a developmental disorder that
resulted in an unusually small brain and a misshapen skull and lower
body.


But arm and leg fossils from LB1 and a second hobbit appear robust,
not unhealthy, according to a new study directed by William Jungers of
Stony Brook University in New York. The bones display humanlike
thickness in the tough tissue that forms the outer shell of most
bones, and opposite sides of the limb bones exhibit comparable
thickness, a sign of healthy growth, said Stony Brook anthropologist
and study coauthor Frederick Grine, who presented Jungers’ paper at
the meeting.


Hobbits also possessed much stronger limbs relative to body weight
than either Homo sapiens or its presumed predecessor, Homo erectus,
Jungers’ team concluded.


Limb strength for H. floresiensis approaches that previously estimated
for more ancient hominid species such as the 3.2-million-year-old
Australopithecus afarensis — a.k.a. Lucy — and 2.3-million-year-old
Homo habilis, according to Junger’s analysis.


These results imply that hobbits were able to engage in vigorous
physical activities that neither modern humans nor H. erectus could
manage. Hobbits may have spent much of their time climbing trees, as
Lucy’s kind did, the Stony Brook researchers propose.


Hobbits’ mix of humanlike and Lucy-like limb traits fits with Jungers’
recent proposal that a primitive, currently unknown hominid species
trekked from Africa to Flores at least 1.8 million years ago and
evolved into H. floresiensis. Earlier suggestions that hobbits
descended from H. erectus (SN: 10/30/04, p. 275) have been dropped.


Junger’s group used computerized tomography images to calculate bone
thickness at points along the length of six hobbit bones from the
upper arm and the upper and lower leg. Five fossils came from LB1 and
one came from another hobbit adult. The researchers then compared
these data to corresponding measures for Lucy, H. habilis and several
hundred people from different parts of the world, including Indonesian
pygmies now living on the Andaman Islands.


Estimates of arm and leg strength for LB1 were generated by comparing
her bone thickness to her height and weight — roughly 3 feet, 5 inches
and 66 pounds, according to Jungers. But hobbit skeptics put LB1’s
height at 4 feet or more, a stature that would imply weaker limbs than
the Stony Brook researchers contend.


In another meeting presentation, Robert Eckhardt of Pennsylvania State
University in University Park argued that a developmental disorder
produced a suite of skeletal abnormalities in LB1 (SN: 11/18/06, p.
330), including irregularly shaped hip joints and tube-shaped upper
leg bones. Junger’s new limb-bone analysis doesn’t address those
points, Eckhardt said.


A variety of developmental disorders produce skeletal traits in people
today that Jungers has labeled as exclusive to H. floresiensis,
Eckhardt added.


At the meeting, he described the case of a woman with a developmental
disorder that resulted in an S-shaped collar bone. Jungers’ team
includes this characteristic in a list of hobbit-specific skeletal
features.


This new twist in the hobbit controversy follows the March 17 online
publication of a paper in Nature concluding that hominids reached
Flores by 1 million years ago. Excavations on Flores yielded stone
tools from sediment dating to that time, reported Adam Brumm of the
University of Wollongong in Australia.


Brumm previously uncovered 800,000-year-old stone artifacts on Flores
(SN: 6/3/06, p. 341). He now suspects hominids reached the island as
early as 2 million years ago.


Brumm’s contention has been challenged by colleagues who believe
natural processes may have moved the artifacts from younger to older
sediment layers.


Earthquakes and flooding are two of many possible ways in which stone
artifacts could have been moved on Flores, noted James Phillips of the
University of Illinois at Chicago.


If Brumm is right, only further fossil finds can determine what type
of hominids reached Flores by 1 million years ago, remarked Robin
Dennell of the University of Sheffield in England. “Until we get that
evidence, we’re stumbling in the dark,” he says.

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