21 May 2006
'Hobbit humans' discovery dismissed
Professor Mike Morwood, of the University of New England, in Armidale, Australia, stunned the science world when he and his team announced the discovery of 18,000-year-old remains of the diminutive new human species, Homo floresiensis on the Indonesian island of Flores in 2003. The hominid, nicknamed "The Hobbit", was thought to be an entirely new species of human, with a grapefruit-sized brain about as large as a chimpanzee's.
In the journal Science, a team lead by Prof Robert Martin of the Field Museum, Chicago, which includes Prof Ann MacLarnon at Roehampton University in London, says that the bones in question do not represent a new species at all. A far more likely explanation is that the bones belonged to a modern human who suffered from microcephaly. H. floresiensis was claimed to be a dwarf derived from Homo erectus, a human ancestor that lived as far back as 1.8 million years ago. This seemed like an appealing explanation because islands are known to play tricks on the evolution of animals, sometimes causing them to shrink due to limited food supplies and the reduced presence of predators. But there is a pattern in this shrinkage and while body size can shrink considerably, brain size always does so moderately.
Using data on the best specimen of the Hobbit, called LB1, the scientific paper points out that to be a dwarfed form of H. erectus, it would have to have been just one foot tall with a body weight of only four pounds to explain such a diminutive brain. "The tiny cranial capacity of LB1, which is smaller than in any other known hominid younger than 3.0 million years old, is demonstrably far too small to have been derived from Homo erectus by normal dwarfing," said Prof Martin.
Small brain size is just one of several problems with the science behind claims that LB1 represents a new species, according to Prof Martin and his colleagues. The primary problem, clashing directly with the tiny brain size, is the sophisticated nature of the stone tools found in the same cave deposits where the fossils were discovered. Based on their size, style, and workmanship, these tools belong to types that are consistently associated with modern humans, or Homo sapiens, according to Prof James Phillips of the University of Illinois at Chicago, and co-author. Such tools have never been associated with H. erectus or any other early hominid, he says: "These tools are so advanced that there is no way they were made by anyone other than Homo sapiens."
Another problem with the science surrounding the interpretation of the Flores fossils is that a distinct species of hominid so closely resembling modern humans but living only 18,000 years ago is inconceivable given that H. sapiens had almost certainly reached Flores by that time, according to Prof Phillips. The team also points out that a recent attempt to rule out the possibility that LB1 could have been microcephalic is flawed. This leaves the theory that LB1 was a microcephalic modern human as the only plausible explanation for the Flores fossils, according to Profs Martin, MacLarnon, Phillips and their colleagues. "There has been too much media hype and too little critical scientific evaluation surrounding this discovery, and it is simply unacceptable that papers should be published without providing proper details of the specimens examined," Prof Martin said.
Sources: BBC News, Geological Society News, Telegraph.co.uk (19 May 2006)