Japanese scientists have waded into a row over the origins of so-called "hobbit" hominids whose remains were found on Flores in Indonesia a decade ago.
The most detailed computerised scan of a skull of Homo floresiensis (Flores man) backs theories that the tiny humans were a local product of evolution. The team said the marooned descendants of a hominid called Homo erectus progressively "dwarfed" to match the availability of food on the island.
The findings are a knock to rival hypotheses that surfaced after an Australian-Indonesian team unearthed the bizarre remains in a cave in 2003. Dubbed after the wee folk in J.R.R. Tolkien's tale, the hominids were just a metre tall, weighed about 25kg and had a brain roughly the size of a chimpanzee's, our closest primate relative.
The find raised huge questions about the human odyssey. Was H. floresiensis a separate species? If so, how come it lived alongside Homo sapiens only 13,000 years ago, when - so far as was known - modern man was the sole strain of human?
A team led by Yousuke Kaifu of the National Museum of Nature and Science in Tokyo measured the brain capacity of "LB1", the most intact specimen out of nine found on Flores, using a computed tomography (CT) scanner. They put the brain size at 426 cubic centimetres, somewhat higher than earlier estimates but still only a third of a modern human brain.
The small brain size, argues the Kaifu team, is consistent with a scrawny descendant of Homo erectus, "upright man", who was the first human to leave Africa. H. erectus lived from about 1.7 million years ago to roughly 50,000 years ago.
Kaifu's team believe Flores man's ancestor was the Javanese version of H. erectus. Its isolated descendants went through thousands of years of shrinkage - a phenomenon known as insular dwarfing - to match availability of food on the island.
Two other ideas have come forward to explain the mysterious folk. One is that they were descendants of a much earlier, small-brained hominid called Homo habilis. But, say critics, no evidence has been found that this human reached Asia.
The other is that the Flores bones are simply those of H. sapiens who suffered from a disability called dwarf cretinism, possibly because of iodine deficiency in their diet. This would have made their brains abnormally small.
But, opponents say, cretinism does not explain how the little hominids were smart enough to kill animals, use fire and wield stone tools to butcher their prey.