Best foot forward: Assembly of the foot of the type specimens (LB1) of Homo floresiensis.
Credit: Djuna Ivereigh/ARKENAS.
SYDNEY: A study of the feet of the 'hobbit' Homo floresiensis adds to evidence that it is a real species and not a diseased or dwarfed modern human – the findings also hint it isn't even a close relative.
The remarkable discovery in 2004 of bones from a one-metre-tall hominin, on the Indonesian island of Flores, sparked a scientific furore. The bones date from around 18,000 years ago, and many believed them to represent a new dwarf species of human, H. floresiensis, which may even have persisted until 8,000 years ago.
Dwarf cretins
Others argued that the only known skull was from a modern human pygmy or someone whose brain was dwarfed by diseases such as cretinism or microcephaly, giving rise to an abnormally tiny skull.
Two new studies found in the British journal Nature today, go a long way toward settling this debate, even as they raise new quandaries that are sure to stoke further controversy.
William Jungers, an anthropologist from Stony Brook University in New York, U.S., led a team of researchers who analysed the reconstructed foot of the fossil. They compared the relative length, proportions and the shape of individual bones to a large sample of foot bones from humans and apes.
They found that, rather than being a shrunken version of a modern human foot, the bones of the fossil exhibited a fascinating mixture of primitive and modern features. In some ways it is very human. The big toe is aligned with the others and the joints make it possible to extend the toes as the body's full weight falls on the foot, attributes not found in great apes.
Primitive hominin
But, in other respects, the foot would have been startlingly primitive: far longer than its modern human equivalent, and equipped with a very small big toe, long, curved lateral toes, and a weight-bearing structure closer to a chimpanzee's.
"The foot evidence adds to the growing and overwhelming evidence that this is not a modern person, but rather a new species", Jungers told Cosmos Online. "These findings make it clear that there was more than one way to be a successful hominin."
Recent archaeological evidence from Kenya shows that the modern foot evolved more than 1.5 million years ago, most likely in Homo erectus. So unless the Flores hobbits became more primitive over time, they must have branched off the human line at an even earlier date.
This suggests "that the ancestor of H. floresiensis was not Homo erectus but instead some other, more primitive, hominin whose dispersal into Southeast Asia is still undocumented," the researchers concluded in their paper.
Companion studies, published online in the Journal of Human Evolution, bolster this theory by looking at other parts of the anatomy, and conjecture that these more ancient forebears may be the still poorly understood Homo habilis. Either way, their status as a separate species would be confirmed.
That still leaves questions about the curiously tiny head of the hobbit – which had a chimp-sized brain of around 400 cm3, a third the size of a modern human brain – seemingly too small even for a legitimate dwarf species.
Hippo brains
In a second paper published this week in Nature, Eleanor Weston and Adrian Lister, palaeontologists at the Natural History Museum in London, showed that a model of brain size reduction in hippos might be used to help explain the very small brain size of H. floresiensis.
Weston's team compared the brain sizes of extinct Madagascan dwarf hippos to that of a modern common hippopotamus, scaled-down by body size. Dwarf hippo brains were found to be up to 30% smaller than their scaled counterparts.
Similarly, when they scaled a modern human brain down to the size of H. floresiensis and then reduced it by a further 30%, they found a volume very similar to that of the H. floresiensis fossil. "This provides evidence for a possible evolutionary mechanism that could explain brain size reduction in humans," said Weston.
Looking at all the evidence, Peter Brown, a palaeoanthropologist at the University of New England, in Armidale, Australia, thinks we may be looking at a new species that last shared a common ancestor with modern humans two million years ago.
"Walked like ducks"
"Evolution is full of experiments – some are successful and some aren't. The Flores skeletons have many primitive features, including the bones of the wrist, the anatomy of the ear region, and the ratio of the arms to the legs. These are features found in our earliest ancestors, the Australopithecines and are not going to be produced by dwarfing," he said.
Maciej Henneberg, an anatomist from the University of Adelaide in South Australia, and proponent of the disease theory of the hobbit, isn't convinced, however. He points out that a human with these proportions doesn't make evolutionary sense – 'hobbits' would have been poor runners and clumsy hunters. "They would have walked like ducks," he quipped.
Henneberg also questioned the comparison with hippos. "It is very difficult to make a parallel between dwarfing of a water-dwelling herbivore and an omnivore which lives on land," he said.
With AFP.
