Comparisons

Argue, who is supervised by renowned ANU human evolutionist Professor Colin Groves, described the results of her morphometric and morphological analysis at the ANU's recent Archaeological Science Conference in Canberra.

She compared anatomical structures of the type specimen of H. floresiensis, LB1, with several modern humans, and many ancient hominins such as H. erectus, H. ergaster, H. habilis, and the Dmanisi specimens.

Cranially, it is most similar to H. ergaster or H. habilis - Argue says this indicates only that H. habilis and H. floresiensis shared an ancestor. But H. floresiensis had long arms in proportion to its legs, and is close to the primitive arm-to-leg ratio of the gracile australopithecine, Australopithecus garhi.

When A. garhi was discovered in 1996, it was hailed as a missing link between Australopithecus and Homo, but is now regarded as the most advanced of the australopithecines.

A. garhi, which lived about 2.2 million years ago, had a cranial capacity of 450cc, less than a third that of modern humans and 33cc larger than that of LB1, the type species of H. floresiensis, which has been set at 417cc according to a study last year by Dean Falk and colleagues. Given the pronounced variation in modern human brain size, A. garhi and H. floresiensis are in the same headspace.

But australopithecines never made it out of Africa. Or did they?

"Floresiensis seems to have evolved around the time of A. garhi, given its primitive arm-leg ratio, whereas H. habilis was moving towards the modern human ratio around the same time," Argue says.

"If we're right, it means some hominin must have moved out of Africa about two million years ago, which is half a million years earlier than the Dmanisi hominin, which is supposedly the earliest out of Africa.

"Not long after H. floresiensis was discovered, someone drew attention to the skull's resemblance to one of the sub-adult skulls from Dmanisi, but morphologically, the Dmanisi crania are very similar and they are quite different from H. floresiensis.

"The 'hobbit' had a relatively small head in relation to its body, and it stood about one metre tall. Australopithecines started at just under one metre, and range up to 1.2 metres, so height is not really an issue.

"We don't have to invoke the island law - the hobbit has some very ancient australopithecine characteristics, which suggest its ancestors were tiny.

"The question is: how did it get to Flores, and when? It's likely to have left Africa between two million and 2.25 million years ago, but that doesn't mean it got to Indonesia immediately - it could have evolved along the way.

"But its presence on Flores means it must have been present on islands back up the Indonesian archipelago. If we knew where to look.

"There is a new Australian-Indonesian program to excavate other targeted areas and it could have reached Flores via Sulawesi, as some others have suggested."