New light shines on ‘hobbit’

A visual comparison of the hobbit's wrist bone scaled to the same size as those of a chimpanzee and a modern human.  The colors indicated the articular and non-articular bone surfaces.
A visual comparison of the hobbit’s wrist bone scaled to the same size as those of a chimpanzee and a modern human. The colors indicated the articular and non-articular bone surfaces.
J.R.R. Tolkien may have talked up their hairy feet, but it is the wrists of hobbits – real hobbits, not the ones in the novelist’s Middle-earth – that interest anthropologists.

An international team of researchers has used ASU’s cutting-edge, three-dimensional imaging technology to help crack the mystery of Homo floresiensis, a 3-foot-tall, 18,000-year-old skeleton nicknamed “The Hobbit.”

The team, led by ASU alumnus Matt Tocheri of the Smithsonian Institution Human Origins Program and ASU doctoral candidate Caley Orr of ASU’s School of Human Evolution and Social Change, used techniques developed at ASU’s Partnership for Research in Spatial Modeling (PRISM) to better place the hobbit on the human family tree. The research was published in the Sept. 21 issue of the journal Science. The work at PRISM was funded by a 3DKnowledge grant from the National Science Foundation.

Four years after they were first discovered on the Indonesian island of Flores, the dozen hobbit skeletons continue to generate heated debate among researchers. Although the skeletons have skull and jaw features similar to modern humans, and the overall structure of creatures that clearly walked on two legs, researchers differ on how best to interpret them.

It is clear that hobbits are a type of hominin – a fossil relative more closely related to humans than to chimpanzees – but while some consider them the bones of a different species of early human, others think they are remnants of a closed community of modern humans with a shared genetic defect or growth disorder.

When the Flores material was first released, they named this new species Homo floresiensis based on a number of features of the cranium and the mandible (jawbone) and its very small stature,” says Orr, who also works in ASU’s Institute of Human Origins. “It had some links in terms of the cranial shape with Homo erectus, an earlier species of hominin, but it’s since been challenged by a number of groups saying, ‘Well, its possible you could explain many of these features as the result of some kind of pathology – microcephaly, and some kind of syndrome that might cause dwarfing.’

Tne approach to answering that question, and to nailing down just where in evolutionary history the hobbit belongs, is to look at the wrist bones.

Modern humans and our closest fossil relatives, the Neanderthals, have wrists that are quite different in shape from those of living apes, older fossil relatives like Australopithecus, or even the earliest members of the genus Homo.

As graduate assistants at ASU, Tocheri and Orr developed a large database of three-dimensional laser scans of primate wrist bones using PRISM. They also developed techniques for comparing the three-dimensional structures of the bones, clustering them into groups such as “great apes” or “modern humans.” Determining which group, if any, the hobbit bones belonged to was simply a matter of getting a hold of some casts of the bones in question, scanning them and comparing them to what they already had.

That is where serendipity stepped in.

While attending a lecture at the Smithsonian Institution by the chief preservationist of the hobbit bones, Tocheri was offered the opportunity to see casts of the skeleton’s wrist.

“Up until then, I had no definitive opinion regarding the hobbit debates,” Tocheri says. “But these hobbit wrist bones do not look anything like those of modern humans. They’re not even close.”

After receiving consent from the research team, Tocheri contacted Orr so that they could pool their data and make the comparison. Just as they suspected, the hobbit bones were nearly indistinguishable from those of an African ape or early hominin-like wrist – nothing at all like wrist bones found in modern humans and Neanderthals.

More importantly, the findings supported the conclusion that hobbits are indeed a branch of early human and not modern humans with some kind of pathology. According to Orr, wrist disorders, even genetic ones, cannot account for such a striking match to early hominin-like wrists.

“Because the development of the wrist bones is so early and the types of pathologies that the critics have talked about tend to occur later on in the development of an individual, it becomes very difficult for pathology to account for a wrist looking the way it does in the hobbit,” he says. “And although there are certainly pathologies that can affect the wrist, it would be highly unlikely that they would produce the anatomy that we are seeing.”

The overall skeletal features of the hobbits, combined with Tocheri and Orr’s wrist analysis, also provides valuable clues as to how long ago the hobbit split from the human family tree.

Humans and Neanderthals share a common ancestor with “modern” wrist bones dating back to about 800,000 years ago, so anthropologists can say with confidence that the hobbits predate that ancestor. Unfortunately, they cannot bracket the dates beyond that, because of a lack of wrist material from other early hominins such as Homo erectus.

Still, the finding, by providing some confirmation of the human ancestor hypothesis, could cause quite a stir in the Shire, as Tolkien might say.

“I think it will make an impact because there are a lot of people who hadn’t made up their minds about the Flores material,” Orr says. “The data are good, and they tell an interesting story that people will definitely consider in terms of making up their mind of what the Flores fossils are – whether they are a distinct species or not.”

Note: This story has been adapted from a news release issued by Arizona State University