Fossils that combine Homo-like skull characteristics with primitive traits in the trunk and limbs are not unprecedented. The earliest members of our genus, such as Homo habilis, also exhibit a hodgepodge of old and new. Thus, as details of the hobbits' postcranial skeletons have emerged, researchers have increasingly wondered whether the little Floresians might belong to a primitive Homo species, rather than having descended from H. erectus, which had modern body proportions.
An analysis conducted by Debbie Argue of the Australian National University in Canberra and her colleagues bolsters this view. To tackle the problem of how the hobbits are related to other members of the human family, the team employed cladistics—a method that looks at shared, novel traits to work out relationships among organisms—comparing anatomical characteristics of LB1 with those of other members of the human family, as well as apes.
In a 2009 paper in the Journal of Human Evolution, Argue and her collaborators reported that their results suggest two possible positions for the H. floresiensis branch of the hominin family tree. The first position is that H. floresiensis evolved after a hominin called Homo rudolfensis, which arose some 2.3 million years ago but before H. habilis, which appeared roughly two million years ago. The second position is that it emerged after H. habilis but still well before H. erectus, which arose around 1.8 million years ago. More important, Argue's team found no support for a close relationship between H. floresiensis and H. erectus, thereby dealing a blow to the theory that the hobbits were the product of island dwarfing of H. erectus. (The study also rejected the hypothesis that hobbits belong to our own species.)
If the hobbits are a very early species of Homo that predates H. erectus, that positioning on the family tree would go a long way toward accounting for LB1's tiny brain, because the earliest members of our genus had significantly less gray matter than the average H. erectus possessed. But Argue's findings do not solve the brain problem entirely. LB1 aside, the smallest known noggin in the genus Homo is an H. habilis specimen with an estimated cranial capacity of 509 cubic centimeters. LB1's brain was some 20 percent smaller than that.
Could island dwarfing still have played a role in determining the size of the hobbit's brain? When the discovery team first attributed LB1's wee brain to this phenomenon, critics complained that her brain was far smaller than it should be for a hominin of her body size, based on known scaling relationships. Mammals that undergo dwarfing typically exhibit only moderate reduction in brain size. But dwarfing of mammals on islands may present a special case. Eleanor Weston and Adrian Lister of the Natural History Museum in London found that in several species of fossil hippopotamus that became dwarfed on the African island nation of Madagascar, brain size shrank significantly more than predicted by standard scaling models. Based on their hippo model, the study authors contend, even an ancestor the size of H. erectus could conceivably attain the brain and body proportions of LB1 through island dwarfing.
The work on hippos has impressed researchers such as Harvard University's Daniel Lieberman. In a commentary accompanying Weston and Lister's report in Nature, Lieberman wrote that their findings “come to the rescue” in terms of explaining how H. floresiensis came by such a small brain.
Although some specialists favor the original interpretation of the hobbits, Mike Morwood of the University of Wollongong in Australia, who helps to coordinate the Liang Bua project, now thinks the ancestors of LB1 and the gang were early members of Homo who were already small—much smaller than even the tiniest known H. erectus individuals—when they arrived on Flores and then “maybe underwent a little insular dwarfing” once they got there.
Artifacts left behind by the hobbits support the claim that H. floresiensis is a very primitive hominin. Early reports on the initial discovery focused on the few stone tools found in the hobbit levels at Liang Bua that were surprisingly sophisticated for a such a small-brained creature—an observation that skeptics highlighted to support their contention that the hobbits were modern humans, not a new species. But subsequent analyses led by Mark W. Moore of the University of New England in Australia and Adam R. Brumm, now at the University of Wollongong, have revealed the hobbit toolkit to be overall quite basic and in line with the implements produced by other small-brained hominins. The advanced appearance of a handful of the hobbit tools at Liang Bua, Moore and Brumm concluded, was produced by chance, which is not unexpected considering that the hobbits manufactured thousands of implements.
To make their tools, the hobbits removed large flakes from rocks outside the cave and then struck smaller flakes off the large flakes inside the cave, employing the same simple stone-working techniques favored by humans at another site on Flores 50 kilometers east of Liang Bua called Mata Menge 880,000 years ago—long before modern humans showed up on the island. (The identity of the Mata Menge toolmakers is unknown because no human remains have turned up there yet, but they conceivably could be the ancestors of the diminutive residents of Liang Bua.) Furthermore, the Liang Bua and Mata Menge tools bear a striking resemblance to artifacts from Olduvai Gorge in Tanzania that date to between 1.2 million and 1.9 million years ago and were probably manufactured by H. habilis.