Indonesia's enigmatic "hobbits" were no more than average humans whose small stature, tiny brains, and peculiar anatomy were caused by a severe lack of iodine before birth, a new study claims. The proposal is the latest salvo in the battle about whether these diminutive people were truly a different species of human, but it's unlikely to end the debate.
The identity of the hobbits has been disputed since they were unearthed on the island of Flores in 2004. Discoverers dated the bones from 12,000 back to 95,000 years ago and claimed that they belonged to a new kind of human, Homo floresiensis, distinguished by its 1-meter-tall stature, chimpanzee-sized brain, and peculiar anatomy. But critics charged that the bones were merely modern humans suffering from microcephaly, dwarfism, or a pituitary disorder known as Laron syndrome (Science, 10 August 2007, p. 740).
Now scientists can add one more theory: cretinism. Cretins' prenatal development is disrupted by a lack of iodine and subsequent hypothyroidism, and they share many of the hobbit's traits, including short stature, argues Peter Obendorf of RMIT University in Melbourne, Australia. He, Charles Oxnard of the University of Western Australia in Crawley, and RMIT colleague Benjamin Kefford found that published images and data from the hobbits "matched up" to those of cretins, who average 70% of normal height. The researchers also noted that the pituitary fossa, a notch in the skull that houses the pituitary gland, was enlarged both in the single hobbit skull and in cretins. They found other shared features as well. For example, in both the hobbit and the cretins, the top of the upper arm bone is unusually straight and untwisted, and both have relatively thick or robust limbs.
Other hypotheses of pathology concerning the hobbit have focused on genetic disorders. But the fact that cretinism can be environmentally triggered may help explain why discoverers found the remains of up to 12 tiny individuals in Liang Bua cave, says Obendorf. Iodine deficiency manifested as goiters is relatively common in the region of Liang Bua cave today, he says, although cretinism, which is due to a more severe deficiency in pregnant women, is not.
Obendorf suggests that the cretins, being less mobile, were perhaps left behind when their hunter-gatherer bands moved on, and so their remains are common in the cave. In the paper, the team even speculates that cretins isolated from the rest of the group might be the origin of local myths of the "Ebu Gogo," small, hairy people who stole food and lived in caves. "I don't think we've proved [cretinism], but the new-species hypothesis is looking pretty weak," says Obendorf, whose team reports its findings in today's issue of the Proceedings of the Royal Society B.
Other hobbit skeptics welcome the study, although many are not yet ready to accept cretinism as the answer. "I am delighted to see that yet another independent group of established scientists has come to the conclusion that [the hobbit skull] is a pathological specimen," says R. D. Martin of the Field Museum in Chicago, Illinois. But he still finds microcephaly a compelling hypothesis to explain the hobbit's puny brain.
Those studying the original specimens and casts thereof aren't buying the latest charge, however. "No way, Jose," says Dean Falk of Florida State University in Tallahassee, who did computed tomography (CT) scans of the lone hobbit skull, LB1. She and others challenge the team's conclusions point by point. For example, using CT scans instead of published photos, Falk finds that the hobbits' pituitary fossa is no larger than usual. The fossa size "is the crux of the argument vis-à-vis cretinism, so pretty much game over," says William Jungers of Stony Brook University in New York state. "The rest is pure speculation." He says there's no evidence that cretins' brains are as small as that of LB1. Debbie Argue of Australian National University in Canberra adds that Obendorf's team has not accounted for hobbit cranial oddities such as a mounding of bone above and around the orbits.
Ralph Holloway, a self-described "fence sitter" on the hobbit question, says he's not leaving his fence yet. "I think [Obendorf's team] is dead wrong on the size of the pituitary fossa," he says, given his own inspection of a cast of the inside of the hobbit skull. "The bottom line is that almost all of the claims for pathology fail to provide evidence that matches what one sees in the Flores remains."