Hypothyroidism hypothesis

So what's the argument? Obendorf, Kefford and Oxnard believe the hobbit's physical features are consistent with human endemic cretins, the product of a hypothyroidism due to a combination of iodine deficiency and thiocyanate toxicity - thiocyanates are cyanogenic compounds present in certain food plants.

Their hypothyroidism hypothesis can account for folkloric descriptions of the appearance of the ebu gogo, and therefore their gluttony, as well as reports that they still existed as little as a century ago.

Their explanation also invokes a pattern of succession evident throughout human history, where a technologically superior culture invades territory occupied by an aboriginal culture, and displaces it from the resource-rich coastal region into marginal hinterlands.

Obendorf says endemic cretinism was the first hypothesis that came to mind after he heard that Mike Morwood and Peter Brown's team had discovered a tiny, small-skulled human fossil in a limestone cave in central Flores in 2004.

He was surprised that no-one considered endemic cretinism as an explanation, given that cretinism, associated with small stature and smaller brains, was not uncommon in limestone regions of Europe, the US, south-east Asia and Australia until iodised salt was recognised as a simple treatment for hypothyroidism and goitre early last century. Endemic cretinism due to maternal iodine deficiency was still occurring in Tasmania in the 1960s.

Occam's razor requires that the first thing is to try to explain the fossil as a modern human. Only if that fails do you consider the possibility that it's a Martian, or something else.

At a conference in Sydney in 2005, the post-cranial remains of Liang Bua 1 (LB1), the first specimen discovered, were discussed.

"I was interested to learn that the humerus (the long bone between shoulder and elbow) was twisted in LB1, to a lesser extent than seen in humans or even apes," Obendorf says.

He quickly found that humeral torsion is a feature of endemic cretinism in humans - iodine deficiency restricts elongation at the growth plates at either end, but lateral expansion is unaffected, resulting in thickening and twisting.

"I thought I was on the right track, but I needed some help from a physical anthropologist who knew the intricacies of bones better than I did," he says.

"I approached Charles Oxnard at the University of WA, who said he had had his own thoughts on the fossils. He was happy to discuss it but said, 'Don't expect me to agree with you.'

"Charles looked at some crania from [myxoedematous endemic, or ME] cretins in the Royal College of Surgeons in Edinburgh, and found a lot of missing features. In ME cretinism, some of the cranial bones remain cartilaginous and are lost during fossilisation - the same bones were missing in LB1.

"That's what got Charles interested. In addition we found that there were lots of experiments in the 1930s in which people experimentally introduced cretinism in growing animals, and showed that the long bones became relatively thick and stunted, consistent with the LB1 long bones."

Obendorf and Oxnard found the cranium displayed many features of congenital hypothyroidism, including an enlarged pituitary fossa - the depression in the wing-like sphenoid bone that houses the pituitary gland at the base of the skull.

Peter Brown disputes this. "Their argument hinges on LB1 having large pituitary fossa," he says. "If they had looked at the original, which I have, they would have seen that it does not."