Analysis of the diminutive cranium of Homo floresiensis - a tiny hobbit-like human that lived in Indonesia just 13,000 years ago - confirms it as a unique species and reveals remarkably advanced features for such a small brain.
The skull and other bones of one female and fragments from up to six other specimens were discovered in caves on the Indonesian island of Flores in 2003 and revealed to the world in October 2004. The remarkably petite human stood just a metre tall and had a brain about one-third the size of modern humans.
But Dean Falk, an expert on brain evolution at Florida State University, US, who has analysed the skull of H. floresiensis says it has some remarkably advanced morphological features, including ones associated with complex brain processes in living humans. "It has an extraordinary morphology unlike anything I've seen in 30 years," she told New Scientist.
This adds weight to the theory that H. floresiensis may have possessed an intelligence and tool-building ability traditionally associated with much larger-brained humans. The charred bones of animals were also found in the caves on Flores. "It may well be that the population was hunting, making tools and using fire," says Falk. "I'm conservative by nature but in light of these features we find nothing to contradict this speculation."
Falk used data collected during CT scans performed shortly after the skull was discovered to build a 3D computer model of the cranial cavity. This mirrors the overall shape of the brain and can even reveal certain surface features. She compared the model to ones made from the skulls of other extinct pre-humans along with those of modern humans and living apes.
Falk found several advanced morphological features, including enlarged frontal and temporal lobes and an extended area at the back called the lunate sulcus. In modern humans the frontal lobes are associated with forward planning and problem solving and temporal lobes are thought to play a key role in memory. The extension of the lunate sulcus is typically associated with a more highly developed ability to analyse sensory information, says Falk.
Disregarding size, the brain of H. floresiensis most closely resembled that of Homo erectus, a human ancestor that disappeared around 70,000 years ago that was thought to have made relatively complex tools.
But Chris Stringer at the Natural History Museum in London, UK, says it may be rash to draw too many conclusions about the intelligence of H. floresiensis from the brain morphology alone. He notes that some features also seem to predate H. erectus. "I reserve judgement on what kind of intelligence and technology the animal might have had," he says.
Stringer adds that the picture is far from simple as the brain has some features unlike anything seen before.
The discovery of H. floresiensis was hailed as the most important anthropological find for 50 years. It alters the picture of human evolution, showing that it have continued until very recently and was more diverse than previously thought.
But the find has stirred up heated debate among anthropologists, a small number of whom refuse to accept it is a unique new species at all. Bernard Wood, an anthropologist at George Washington University, US, says the model should at least dispel dissenting claims that the remains are not a unique species but simply a modern human with microcephaly, a rare condition that results in a reduced cranium size.
"Unequivocally, it is not what you would expect a miniaturised modern human brain to look like," Wood insists. "Nor is it like the brain of a human with a pathological microcephaly."
Journal reference: Science (vol 307)
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