A miniature species of extinct humans, nicknamed "hobbits", possessed unusual anatomical features explained by their complete isolation from the rest of humanity for thousands of years on their remote island home in Indonesia, studies have found.
The tiny people, who grew to an adult height of no more than three feet, astounded scientists in 2004 when a skull and partial skeletons were unearthed from a cave on the island of Flores. Radiocarbon dating suggested that the species, Homo floresiensis, had lived in and around the cave for tens of thousand of years before dying out about 17,000 years ago.
The latest research into H. floresiensis has found that they were flat-footed, long-toed creatures who could walk easily on two legs but would have found it difficult to run at speed. A separate study suggests that their very small heads, which were perfectly in proportion to their bodies, were the evolutionary outcome of living on such a remote island for so long.
Two studies published in the journal Nature also cast further doubt on the idea that the hobbits were ordinary people suffering from some kind of pathological condition, such as microcephaly – when the skull fails to grow normally. Many scientists believe there is now little doubt that the hobbits were indeed a human species who had evolved as a result of island dwarfism, when larger animals gradually become smaller over the generations.
"That evidence has been overwhelming for some time now. Our study provides additional and unequivocal confirmation that we're dealing with a new species. The pathology debate is officially over," said Professor Bill Jungers of Stony Brook University in New York, who led the study into the hobbit's foot bones. "Their big toe was surprisingly short and more similar to a chimpanzee's in relative length than to humans.
"However, like chimpanzees again, the free parts of the lateral toes were relatively very long and the bones within were curved, whereas human toes in this region are short and straight," Professor Jungers said.
The investigation of the hobbit's foot bones also revealed that the miniature humans lacked an arch. In other words, they were flat footed. "They still walked just fine despite having relatively long feet and funny proportions, but they needed to lift their feet a little higher off the ground to clear their toes, possibly by flexing their ankles or knees more. They were designed quite adequately for walking, but were poorly adapted for long-distance running," Professor Jungers said.
A range of small stone tools found alongside the bones suggest that the hobbits hunted and butchered local animals that lived on the island at the time, such as pygmy elephants, giant rats and reptiles, such as the Komodo dragon. But their ancestral origins remain a mystery.
The long toes of H. floresiensis suggest they could be the direct descendants of a hominin similar to an early human ancestor such as H. habilis, rather than the more recent H. erectus, a species known to have migrated out of African long before the migration of our own species, H. sapiens.
Alternatively, the hobbits may be the descendants of a dwarfed H. erectus that not only underwent a miniaturisation of its body, but reverted to more primitive features. Professor Jungers said that both scenarios are possible, although at present he favours the idea that the hobbits were descended from a bipedal hominin that had escaped Africa before H. erectus.
A separate study by researchers from the Natural History Museum in London investigated the problem of the hobbit's very small skull and brain by comparing it with the skull of extinct pygmy hippos that lived on the island of Madagascar. Like the hobbit, the hippo's skull had become smaller over time and in perfect proportion to the miniaturisation of its body.
Eleanor Weston, who led the study, said that the hippo shows for the first time that island dwarfism results in the miniaturisation of skull and brain seen in the hobbit. Dr Weston said: "Whatever the explanation for the tiny brain of H. floresiensis relative to its body size it is likely the fact it lived on an island played a significant part in its evolution."
Intelligence test: The concept of island dwarfism
A key difficulty with the idea that the hobbits are a new species of human is that their brains are so small. How could a brain about the size of a grapefruit provide the intelligence to make and use the exquisitely carved stone tools found alongside the bones of H. floresiensis?
Adrian Lister and Eleanor Weston of the Natural History Museum in London believe that their expertise in studying "island dwarfism" in other animals has resolved the problem. Their study of an extinct species of dwarf hippo on the island of Madagascar showed for the first time that skull and braincase do indeed become smaller in direct proportion to the miniaturisation of other parts of a dwarfed body. In other words, the exceptionally small head and brain of H. floresiensis can be explained by evolutionary pressures resulting from living on an island, rather than the result of some kind of medical condition. And they seemed to have lived happily with small brains.
Island dwarfism is a well-known phenomenon. Extinct pygmy mammoths have been found on Wrangel Island in Siberia, along with dwarfed elephants on Mediterranean islands. Dwarfism is a way of surviving the limited resources of an isolated habitat, Dr Weston said.
"We found that the brain sizes of extinct dwarf hippos were up to 30 per cent smaller than you would expect by scaling down their mainland African ancestor," said Dr Weston. "If the hippo model is applied to a typical H. erectus ancestor, the resulting brain capacity is comparable to that of H. floresiensis."