The tale of Homo floresiensis 鈥� aka the hobbit 鈥� is beginning to read less like a Tolkien epic than an Agatha Christie whodunit.
Two studies add a new twist to the plot. One claims that the skeleton鈥檚 ape-like feet push back its ancestry near the dawn of Homo. Another argues that the hobbit is a later offshoot of Homo erectus, dwarfed by aeons of island isolation.
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鈥淓ither answer is pretty damn exciting,鈥� says , a palaeoanthropologist at Stony Brook University in New York, who led the analysis of the foot. 鈥淚t鈥檚 telling us something pretty amazing about human evolution.鈥�
Hobbit skeleton
Researchers unearthed the hobbit鈥檚 18,000-year-old skeleton in Liang Bua Cave on the Indonesian island of Flores in 2003. Then in 2004 partial remains from at least a half dozen individuals were uncovered.
Much subsequent research has focused on the skull, which encased a 417 cubic-centimetre brain 鈥� about the size of a chimpanzee鈥檚 and a third the size of a human adult brain.
Since island species, separated from their mainland kin, tend to shrink over evolutionary time, the main thrust of the 鈥渉obbit as separate species鈥� arguments have focussed on its small brain. However another theory holds that the skull is simply that of a diseased Homo sapiens.
Lack of resources could select for smaller and smaller bodies, and some researchers argue that power-hungry brains can shrink even more drastically than the rest of the body.
Island dwarf
鈥淚t might be advantageous to the animal not to invest in such a large organ,鈥� says , a palaeontologist at the Natural History Museum in London, whose new study contends that H. floresiensis was an insular dwarf of H. erectus.
But even scaled down to the hobbit鈥檚 1-metre, 30 to 40 kilogram frame, H. erectus would boast a brain of 500 to 650 cubic centimetres 鈥� small but still too big to explain the Hobbit skull.
However, Weston contends that such figures underestimate the dwarfing of mammalian brains that actually occurs on islands. She and colleague Adrian Lister compared two extinct species of dwarf hippopotami found on Madagascar with the modern, full-sized beasts found only on the African mainland.
True brain size
The dwarf species went extinct in the past 1000 years, and they diverged from mainland hippopotami sometime between 50,000 and two million years ago, Weston says.
Using more than 30 full-size hippopotami of varying age and size as reference points, Weston and Lister calculated the scaled-down brain size of 24 dwarf hippos. These models consistently overestimated the true size of the dwarf鈥檚 brains by about 24 or 30 per cent.
鈥泪蹿 Homo floresiensis really had undergone this process of dwarfing, potentially something like Homo erectus could be the ancestor,鈥� Weston says.
Applying a scaling factor to a dwarfed H. erectus comes up with Hobbit-sized brain that鈥檚 between 378 and 493 cubic centimetres, depending on the H. erectus specimen used.
Bizarre foot
鈥淢y problem with that is that it doesn鈥檛 speak to the rest of the skeleton,鈥� says Jungers, who also presented his analysis of the hobbit鈥檚 bizarre foot at an anthropology conference last year.
For starters, the feet of H. floresiensis are far longer than would be expected of 1-metre tall H. erectus or H. sapiens. The resulting need to drag its feet back high with each step to avoid kicking the ground would have limited its ability to move swiftly. It also has unarched feet. 鈥淚t鈥檚 never going to win the 100-yard dash, and it鈥檚 never going to win the marathon,鈥� Jungers says.
Both features also point to an ancestor that predates fleet-footed H. erectus, Jungers says. 鈥泪蹿 in fact human evolution redesigned the bipedal foot in some way, these guys missed the train.鈥�
A closer inspection of the bones in the hobbit鈥檚 nearly complete left foot reveal both modern and archaic characteristics. Its short big toe resembles that of an australopithecine like Lucy, while the shapes of the toe bones appear human. 鈥淚t鈥檚 definitely a head-scratcher,鈥� Jungers says.
He speculates that the hobbit鈥檚 closest relative is a species of human more ancient than H. erectus, with a smaller brain 鈥� perhaps H. habilis.
Satisfying theory
, a palaeontologist at Chicago鈥檚 Field Museum not involved in either study, says Jungers鈥� explanation is more satisfying than the idea of a H. erectus, dwarfed by island-life. 鈥淭hat could explain the small brain without requiring any major reduction,鈥� he says. But adds that there is no indication in the fossil record that any human species older than H. erectus travelled beyond Africa.
However, Martin still thinks the hobbit is an unusually small human that suffered from a developmental disease, possibly microcephaly.
鈥淭his needs to be confirmed by some fossils,鈥� says Jungers, who hopes a five-year excavation of other spots in Flores that鈥檚 in the works will determine what the ancestors of the Hobbit looked like.
Journal reference: Nature (DOI: Weston鈥檚 study: 10.1038/nature07922 and Junger鈥檚 study: 10.1028/nature07989)
