before it's in the papers"
August 03, 2010
TO THE WORLD SCIENCE HOME PAGE
Race of tiny people didn’t exist, scientists say
and World Science staff
When scientists found 18,000-year-old bones of a small, humanlike creature on an Indonesian island in 2003, they concluded that the bones represented a new species in the human family tree.
The conclusion was widely accepted among scientists and trumpeted by the press. Because of its size, the creature was dubbed the “Hobbit.”
But a growing number of scientists have raised questions about the claims.
In a new paper, a team of scientists says the bones are probably just from an ordinary person who suffered microcephaly, or small-headedness. “There has been too much media hype and too little critical scientific evaluation,” said primatologist Robert D. Martin, provost of the Field Museum of Chicago and the paper’s lead author.
He blasted some of the research that went into it as “unacceptable” in quality.
But supporters of the initial finding gave no ground. They argued that Martin’s own studies of the specimens are the ones lacking detail and focus.
The proposed new hominid species was given the scientific name Homo floresiensis, due to the fossils’ discovery on Flores Island. Its interpretation as a new species was based on a specimen labeled LB1, consisting of a little adult skull and partial skeleton about three feet (91 cm) tall.
It was initially described as a “dwarf” species related to Homo erectus, a human ancestor that lived as long as 1.8 million years ago. The account was appealing because islands are known to play tricks on the evolution of animals, sometimes making them shrink due to shortages of food and lack of predators.
But all mammals that have shrunk for those reasons, or any others, have done so within certain parameters, Martin and colleagues argued in their paper, in the May 19 issue of the research journal Science. Body size can shrink considerably, but brain size always shrinks moderately.
LB1’s 400-cubic centimeter brain is too small to follow this law, they argued. For it to be a “dwarfed” form of H. erectus, they added, it would have had to be just one foot (30 cm) tall and weighed only four pounds (less than 2 kg) to explain such a tiny brain.
Also, they wrote, sophisticated stone tools found near the fossils contradict the tiny brain size. Based on the tools’ workmanship, “there is no way they were made by anyone other than Homo sapiens,” our own species, which had almost certainly reached the island by then, said the Field Museum’s James Phillips, an anthropologist and member of Martin’s group.
Some scientists have suggested the microcephaly interpretation of the fossils before. Supporters of the original interpretation have rejected it, based on studies of a known microcephalic skull. Their analysis found that the skull was clearly different from the Flores Man specimens.
But Martin countered that the skull this group used was a poor comparison piece because it came from a 10-year-old and is a defective plaster copy made of two parts that don’t match. Moreover, Martin and colleagues argued, the study had involved just that one skull, whereas microcephaly takes dozens of forms.
This copy “is inappropriate for any scientific study,” Martin said. “It was the worst possible choice… [it] is one of the smallest that I have so far found in a survey of over 100 human microcephalics.”
Defenders of the original findings shot back in a response published in the same issue of the journal.
First, they wrote, they weren’t claiming—as Martin’s group implied—that the fossil represented a straightforward miniaturization of H. erectus.
The first report on the new fossils did suggest something to that effect. But the later study with the microcephalic skull cast had raised some problems with this. Its authors had suggested an alternate possibility that both species descended from a common ancestor.
The fact that researchers studied microcephalic skull from a 10-year-old is unsurprising, as most microcephalics die very early, wrote the authors of the response. The authors, Dean Falk of Florida State University in Tallahassee, Fla., and colleagues, included scientists involved in both the initial, 2004 report on H. floresiensis and in the later microcephalic skull study.
A competing analysis of microcephalic skulls from Martin’s team is flawed, the group added. “The line drawings they present as evidence lack details about the transverse sinuses, cerebellum, and cerebral poles,” important structures, they wrote.
“Comparative measurements, actual photographs, and sketches that identify key features are needed to draw meaningful conclusions,” they added, arguing that these were absent. “Without this evidence, the assertions of Martin et al. remain unsubstantiated and difficult to address in further detail.”
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