· Bone analysis supports distinct species theory
- The Guardian
- Friday September 21 2007
It was the most astonishing anthropological find of a generation - a diminutive new species of human that apparently shared the planet with us until 13,000 years ago.
But the discovery of the fossilised "Hobbit", as she quickly became known, has provoked a long-running and sometimes acrimonious debate among scientists: was she really one of a race of mini-humans or was she merely one of us, but with a brain-shrinking disease?
Now scientists have analysed fossilised wrist bones that were part of the original discovery in 2003 but had not been looked at in detail. They say they prove the Hobbit really was a distinct and previously unknown type of human, and not just an abnormally small member of our own species.
That analysis has revealed significant differences between the bones and human or Neanderthal equivalents. At the same time there are crucial similarities with older species of human and living apes such as chimps and gorillas. The researchers say this puts paid to the idea that Homo floresiensis could be a "normal" human being with a brain-shrinking disease called microcephaly or some form of dwarfism.
The Hobbit was remarkable because of where it was found and when it was supposed to have lived. Its existence alongside modern humans 13,000 years ago is more than 15,000 years after the Neanderthals died out and more than 140,000 years after modern humans evolved in Africa.
"What we are beginning to realise is that our recent evolutionary history is much more diverse than we realised," said Matthew Tocheri of the Smithsonian Institution, lead author on the paper in Science that describes the wrist bone analysis. "It's a little shot to our over-inflated modern human egos."
For some though that interpretation is just too incredible. Robert Martin at the Field Museum of Chicago argued in a paper last year that the Hobbit's grapefruit-sized brain was simply too small compared with its body to be a scaled-down human species. He also said that tools found with the fossils were too advanced to have come from a creature with such a small brain. Meanwhile, Robert Eckhardt at Pennsylvania State University argued last year that Flores, the Indonesian island on which the Hobbit was found, was too small to support a population of hunter gatherers without immigration from other islands. That would mean it was not genetically isolated and so could not have evolved into a separate species. He criticised other researchers' willingness to get caught up in the hype and sniped that, "critical faculties were suspended on the part of many people".
Even the bones themselves have not escaped the intellectual tug of war. Almost as soon as H floresiensis hit the public consciousness in 2004, they were taken - some say borrowed, some say "hijacked" - by a researcher who was not involved in the original find.
But proponents of the separate species hypothesis say that evidence is stacking up in their favour. "I think slowly but surely the facts are coming out," said Dr Tocheri. His own analysis shows that the wrist bones of H floresiensis are not like ours or Neanderthals'. "Even if you are not trained as an anatomist, I think it is clear that the bones look very similar to what we see in living chimps and gorillas today, as well as earlier hominin fossils like Australopithecus - or Lucy," he said, "The wrist evidence is definitely a smoking gun ... I would say that it is proof that it is not a modern human - microcephalic, normal or otherwise."
Crucially, the shape of the wrist forms very early in a baby's development in the womb, in the first three months. Genetic problems leading to small brains or dwarfism tend to hit later or after birth. "It would be extraordinary if a pathology could revert three wrist bones to this morphology," said Chris Stringer, an expert on human evolution at the Natural History Museum. "To have three bones which show this complex of features really does add to the case that this is a distinct and very peculiar human-like creature."
He is open to the possibility that it might yet turn out to be a small-brained human, but he thinks the tide is turning in favour of it representing a much more primitive and distinct species.
"There is a lot at stake. One group of people are going to be 100% wrong in what they have said, which is a situation that is rare in science," he said. "It will be a fascinating test case for science. Will the people who turn out to be wrong hold their position to the bitter end regardless of the evidence that accumulates?"
"As good scientists, we should all be pleased to have new data, even when it proves us wrong, but also being human beings it doesn't always work that way. We have human flaws like everyone else," added Prof Stringer.
Critics of the separate species explanation, however, show no sign of conceding. "If the evidence provided by the wrist bones is so important, why was it not part of the original description and diagnosis of the new species?" said Dr Eckhardt. "The answer is that the wrist bone evidence is not important in and of itself, but rather as a last ditch effort to save the supposed new species by finding some new "unique" feature."
"This is an exercise in the presentation of misleading ideas in an obfuscatory manner. In that sense, then, their paper is far from a model of how science should be done."
Body of evidence
September 2003 'Hobbit' discovered by Indonesian and Australian team on the island of Flores, in Indonesia. It is also called Ebu, after a local legend about a small waddling creature with a big appetite.
October 2004 The findings of a skull and partial skeleton are published in Nature. The team classify the metre high creature as a new species, Homo floresiensis
February 2005 A computer generated model of the skull suggests it did not have an abnormal brain.
October 2005 Australian scientists announce the discovery of more bones including another jaw bone. These confirm the creature's diminutive size, but the haul does not include a skull.
May 2006 Researchers claim the Hobbit's brain is far too small to be microcephalic.
August 2006 Another study claims that Flores is too small to have supported a population without immigration from other islands - so they could not have evolved in isolation.