All in the wrist action: A visual comparison of the hobbit’s wrist bones scaled to the same size as those of a chimpanzee and a modern human (trapezoid in the top row, scaphoid in the centre and capitate in the lower row).
Credit: Science
SYDNEY: A new analysis of the wrist bones of the 'hobbit' – the metre-high hominid whose ancestry has been fiercely debated – adds to evidence that the species is distinct from modern humans.
The wrist evidence adds to other morphological evidence that H.floresiensis is a very ancient human species from Africa, that was isolated and evolved independently on the island of Flores, said study co-author Mike Morwood from the University of New England in Armidale, Australia.
Homo floresiensis, which may have co-existed with our own species as recently as 18,000 years ago, has been dubbed the hobbit due to its diminutive stature. Since the discovery of a relatively complete skeleton on the Indonesian island of Flores in 2003, experts have squabbled over whether H.floresiensis is a unique species of ancient human or merely a deformed individual of our own species.
Ape-like wrists
Some scientists argue that it's morphology and small size, especially its grapefruit-sized skull, can be attributed to a developmental growth disorder called microcephaly. However, the new study detailed today in the U.S. journal Science refutes that claim.
Upon looking at casts of the wrist bones of the specimen known to anthropologists at LB1, or 'Flo', lead author Matthew Tocheri of the Smithsonian Institution in Washington DC immediately saw that they appeared very unusual. He likened them to the wrist bones of apes or much more ancient human ancestors. They "certainly weren't [like] modern human or Neanderthal bones," he said.
Tocheri, an expert on the evolution of wrist bones who was not previously embroiled in the hobbit debate, said it is pure luck that bone casts passed through his hands at all.
Most of Flo's bones recovered from Flores were too soft and delicate to withstand the casting process. But on a recent trip to Indonesia, fossil conservator Lorraine Cornish of the Natural History Museum in London, U.K., decided to attempt to cast some small, seemingly insignificant wrist bones. On the way to New York to deliver the casts to a colleague, Cornish stopped off to give a presentation at the Smithsonian, which Tocheri happened to attend.
"The probability of how these bones ended up at the Smithsonian and how I got to look at them is pretty astounding," Tocheri said. "You can imagine my surprise that the main specimen preserved was the [same kind of] bones that I'd spent the last five and a half years working on. I was just at the right place at the right time."
The researchers used lasers to scan and map the shape of the bones, and Tocheri's previous work on wrists showed that a key bone, the trapezoid, differs quite markedly between apes and humans.
Great apes have a pyramid-shaped trapezoid that helps transmit force along the length of the hand and wrist, allowing more generalised, flexible motion, he said. In modern humans, however, the same bone resembles a rectangular boot shape that helps distribute force across the wrist to generate more force in a smaller range of motion.
"Fistful of evidence"
The analysis suggests that H.floresiensis had wrist bones that are more similar in shape to those of apes or early human ancestors such as the species Australopithecus, than they were to those of modern humans.
Tocheri confirmed that a developmental disease, such as microcephaly, could not explain the unusual anatomy of the hobbit wrist. "There are a lot of things that can go wrong with the wrist, but none of them [cause the bones to become] indistinguishable from a chimpanzee's. I've seen what pathological human wrists look like and it's not what you see in the chimpanzee."
"There was never any skeletal evidence to support their claims [of a deformed modern human], and there is now a fistful of evidence demonstrating that they were wrong," commented palaeoanthropologist Peter Brown of the University of New England in Armidale. "H.floresiensis is a valid species, unrelated to Homo sapiens, with an African root earlier than 1.8 million years ago."
"It is looking less likely that H.floresiensis arrived on Flores as a large-bodied Asian Homo erectus and then dwarfed" as had otherwise been suggested, added Brown. He believes the study could be evidence that early humans left Africa prior to 1.8 million years ago and much early than is currently accepted.
The Homo floresiensis Debate
I love these types of arguments but frankly, I wish there were more specimens available to address these ongoing debates. It’s getting tiresome hearing this wrangling about this single find. The discovery of Homo floresiensis could be one of the great stories in human evolution and hopefully we’ll know more once the original research team gets back to the caves in Flores and to the other islands. Hard to believe, but their work was halted by the Indonesian government at one point further adding fuel to this mess.
Of course, I have a vested interest in this discovery, having written a fictional adventure novel called Flores Girl on the recent fossil find. If you are interested, there is more on this ongoing controversy about Homo floresiensis at www.floresgirl.com or catch the free Flores girl podcast at Pdiobooks.com.
Erik John Bertel