Endemic cretinism

The Obendorf team conclude that the hobbits could have been ME human cretins, members of an inland population of mostly unaffected modern humans - possibly the descendents of Flores' original negrito inhabitants.

Short-statured Negrito populations are found on the Andaman Islands in the Bay of Bengal, and in remote inland regions of the Malay Peninsula, Thailand, and the Philippines. They are believed to be descendants of one of the first wave of modern humans to migrate out of Africa some 60-70,000 years ago.

In their PRS:B paper, Oxnard, Obendorf and Kefford - an aquatic toxicologist who performed the multivariate analyses - note that ME cretins are born without a functioning thyroid, resulting in congenital hypothyroidism.

In neurological cretinism, the skeleton grows normally, but the function of both the brain and peripheral nervous system are severely impaired. Affected individuals suffer mental retardation and impaired motor coordination.

ME cretinism is characterised by restricted bone growth and severe dwarfing, and swelling of soft tissues, resulting in a pot-bellied appearance. Despite their reduced brain size, individuals show less mental retardation and motor impairment than neurological cretins. They learn little language.

Obendorf says certain characters in LB1 that have been interpreted as primitive, including the morphology of the wrist, and a double-rooted lower premolar tooth may be explained as consequences of endemic cretinism.

Endemic cretinism was once common in limestone areas of Europe that formed from uplifted sea floor.

Over time, weathering depletes limestone landscapes of micronutrients, especially iodine and selenium. Obendorf says that in the Carpathian mountains, iodine deficiency was historically exacerbated by high levels of cabbage in the diet - eating cabbage generates high levels of thiocyanates in the serum, that affect the thyroid's ability to synthesise thyroxin.

In central Africa, consumption of cassava had the same effect on populations in limestone areas.

"All these factors are present in Indonesia, in regions like Aceh province on Sumatra, and in Borneo, where there was a high rate of ME cretinism," Obendorf says.

"People did not practice agriculture on Flores, or anywhere else, at that time, so we investigated what wild plants they might have used as foods, and found a number of candidates including a bitter yam, Dioscorea, bamboos, which are high in cyanogenic glucosides, and possibly Acacia seeds."

The age of the Floresian hobbit fossils spans the period between the height of the last glacial period (18kya) and the end of the last ice age, when reduced precipitation would have reduced plant growth and animal numbers in the elevated limestone hinterland of Flores.

Like Australia, Flores and the other islands of Sundaland are also affected by El Nino droughts, which would force people to eat plant foods they might not eat normally - possibly accounting for the episodic appearance of ME cretinism.

"We believed the area would be limestone and selenium deficient, like central Java. ME cretinism would have been a problem until the hunter-gatherers assimilated into farming communities which were spreading out from the coast.

"The farmers would also have had close links with fishermen on the coast, and may have traded some of their food for fish, which contain iodine from sea salt."