The newly-discovered 'hobbit' skull (left) is compared to that of a modern human (right) at a press conference in 2004.

Credit: AFP

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PARIS: A tantalising new piece of evidence has been added to the puzzle over so-called 'hobbit' hominids found in a remote Indonesian cave and whose discovery has ignited one of the fiercest rows in anthropology.

A study released today backs up evidence that Homo floresiensis was a dwarf race that may have evolved through a natural evolutionary tendency for island species to get smaller.

Anthropologists have been squabbling bitterly since the fossilised skeletons of tiny hominids - dubbed after the diminutive hobbits imagined by J.R.R. Tolkien - were found on the Indonesian island of Flores in 2003.

Measuring just a metre tall and with a skull the size of a grapefruit, the diminutive folk lived around 18,000 to 80,000 years ago and appear to have been skillful toolmakers, hunters and butchers.

Their discoverers contend the cave-dwellers were a separate species of human that descended from the extinct Homo erectus, who are also presumed to be the ancestors of modern man. That claim has huge implications and has been widely contested.

If true, it would mean that our own species - H. sapiens, who have been around for around 150,000 to 200,000 years – would have shared the planet with a rival human species far more recently than thought. And it implies that H.sapiens and H.floresiensis lived side by side on Flores for a while – and may even have interbred.

Now, In a study that appears today in the British journal Biology Letters, evolutionary zoologists at Imperial College in London, U.K., argue that the hobbits could easily have evolved from a larger human species, such as ourselves, via a well-recognised evolutionary tendency.

This tendency is called the 'island rule'. It stipulates that because food on a small island is limited, smaller species do relatively well and often get bigger over time compared to their mainland relatives. This is because they can manage well on little resources and out-compete bigger species.

Larger species, on the other hand, face fierce competition for a small amount of food and become smaller, because those members that eat less have an advantage.

Lindell Bromham and Marcel Cardillo trawled through published journals and online databases to see how primates performed when subjected to the island rule.

True enough, small primate species (ones weighing less than five kilograms) all pumped up compared to their mainland relatives. But they also found that all the larger primates became smaller - by as much as 50 to 80 per cent.

That fits in well with what we know of H.floresiensis, who was around 55 percent of the mass of a modern Indonesian and probably 52 percent of an H.erectus.

So the evidence backs the idea that the hobbits were an 'insular dwarf race' – humans who became smaller, possibly after the island separated from the mainland and left them marooned with diminished food resources. The authors refuse, though, to wade into the debate as to whether the hobbits were H. erectus or H. sapiens.

Also unclear is why the hominids had a relatively under-sized brain compared to their diminutive body. A modern human child of the same size has a much larger brain, as do pygmies.

A conflicting explanation for the small brains has been offered by primatologists led by Robert Martin of the Field Museum in Chicago, U.S.. He contends that the Flores hominids were not a separate species but quite simply a tribe of modern humans who suffered from a pathological condition called microcephaly, which results in a small brain and body.

Martin also disputes the idea that these pint-sized creatures could have wielded the sophisticated stone tools, found in the Flores cave, which were used to butcher animals.

The hobbits are thought to have tucked into a now-extinct miniature elephant, Stegodon, that also dwarfed-down under the island rule.