Tuesday, March 11, 2008

Those Pesky Hobbitses! The Ongoing Row about Homo floresiensis in Anthropology and Australia

"Hobbit" is the name being used in common parlance to discuss the seemingly human, albeit miniaturized remains found in Liang Bua cave on Flores island in Indonesia. They were discovered in 2003 by an international team of scientists led by archaeologist Michael Morwood and accompanied by paleoanthropologist Peter Brown, both of University of New England, Armidale, Australia. The team that discovered these remains claim that they constitute a new, heretofore unseen species of hominid that they call Homo floresiensis. The initial findings include the remains of two individuals, tagged as Liang Bua(LB) 1 & 2. Since the initial discovery, components of seven individuals have been found, but LB1 remains the most complete subfossil skeleton to date. LB1 is fully bipedal, has Homo sapiens like teeth, a receding chin, stood at about 1 meter(~3 feet), possesses a femur and pelvis similar to that of Australopithecus afarensis and is thought to have been an adult female(estimated age of 30). The brain of LB1 is about 400 cubic centimeters. Studies conducted by Dean Falk of Florida State University have found that though LB1 is comparable in brain size to A. afarensis(around 385 cubic centimeters, on average), the characteristics of the brain as found on the endocast more closely resembles the brain of a Homo erectus despite the size differential(H. erectus brains averaged 900 cubic centimeters).

Due to the amalgamation of traits that the Liang Bua cave finds possess, various theories have been put fo
rward to explain them. The first theory was posited by a majority of the members on the research team that discovered these subfossils. They claim that H. floresiensis are descendents of H. erectus. The small size of the brains and bodies of H. floresiensis in comparison to average H. erectus is said to be an adaptation to the environment through endemic dwarfism which occurred in response to the scarcity of resources found on the island. Endemic dwarfism, they argue, has been found in other large mammal species living in island environments and so they feel that this should not be discounted as a possibility. They support this with the evidence of fire usage, tool usage and animal bones at the site that indicate that they were intelligent and cooperative hunters.

Other ideas put forward argue that the dwarfism displayed in these specimens is not a product
of the evolutionary environment, but is instead solely genetic in nature. These genetic dwarfisms include postnatal growth retardation, pituitary dwarfism, microcephalic dwarfism and Laron Syndrome. All of these hypotheses have merited rebuttals.

On March 4, 2008, the Proceedings of the Royal Society B(Biological Sciences) published a paper in their online journal titled "Are the small human-like fossils found on Flores human endemic cretins?" by Australian scientists Peter Obendorf, John Oxnard and Ben Kefford. They contest the attribution of species status to the Liang Bua finds and state that the peculiarities of form found in these samples can be explained by environmental factors. Specifically, they state that these specimens are Homo sapiens that suffered from endemic congenital hypothyroidism(aka cretinism). Congenital hypothyroidism is a disorder that exists because of severe iodine deficiency while in utero, causing individuals gestated in these conditions to be born without a functioning thyroid gland, leading to dwarfism and reduced brain size. Many of the other 'primitive' traits that LB1 possesses are explained as being signs of the disorder. This argument is based largely upon the supposed existence of an enlarged sella turcica(aka the pituitary fossa), a depression in the base of the skull where the pituitary gland rests, that is charac
teristic of the disease. They attempt to support their idea through comparison of 2D-CT scan reproductions of LB1's endocast with the cranial measurements of microcephalics and cretins, as provided in studies conducted by others. Though they were unable to find any publications featuring such a severe hypothyroidism that had been documented as having historically caused a drastic reduction in brain size as found in LB1, they cited undernutrition and post-mortem deformation as potential factors having affected brain size in LB1.

This paper has produced quite a negative reaction within the anthropological community and has translated into a significant amount of press in newspapers, journals and blogs. The main points of criticisms have thus far been unsound methodology, statements not backed by tangible information,
and usage of incorrect data. They have also received criticism for never having personally handled the remains(they used "captured images from X-ray scans presented in The mystery of the human hobbit(BBC Horizon, 2005)" to measure the sella turcica (Obendorf et al.)), for having little to no experience with hominid subfossils, and for not being paleoanthropologists. One blogger has even called the article "a failure of peer-review." Peter Brown, a member of the original team has become rather prolific in the media as of late and has made many comments regarding his feelings and the Obendorf et al. study. He critiqued the paper for "being complete nonsense...without a glimmer of factual support." Colin Groves, a biological anthropologist from Canberra's Australian National University stated to the press "I recall spending an hour or so in the pub with Peter Obendorf about three years ago when he confided to me about this lastest bee in his bonnet...I warned him that he would be simply laughed to scorn if he produced what is mainly idle speculation." The most colorful statement about the study comes from evolutionary anatomist and paleoanthropologist William Jungers at Stony Brook University, saying that the paper "is a rather large and stinky pile of misinformation and wild speculation."

Obendorf et al.'s main argument for endemic congential hypothyroidism on Flores is hinged upon the enlargment of the sella turcica(pituitary fossa). They state that the length of the sella turcica is 12.9mm, a size which is disproportionately large for an individual with a brain of that size. This point has been emphasized in the press and addressed by well-respected scientists who have studied endocasts of LB1'a braincase. Dean Falk, in a news piece in the journal Nature, stated "There is no way they can reach the conclusions the did." She stresses that the maximum possible length would be 9mm. Ralph Holloway, of Columbia University, New York indicated that though this particular area on his endocast "is not the best preserved, but even still, I cannot see where it was possible that the pituitary fossa showed enlargement."

It is very likely that Obendorf et al. are wrong in their estimate of the size of the pituitary fossa if only because they measured it using a 2D representation of a 3D-CT scan that they captured from a TV show. Had they access to a photo or an endocast, their measurement would have been demonstrably more accurate. Again, Peter Brown makes an appearance and asserts that "I'm the only person on the planet to have seen what's left of the pituitary fossa. It is very poorly preserved and not capable of meaningful measurement." The problem within this particular statement is that very few people have had access to the specimens from Liang Bua. John Hawks critiques this particular comment by Brown and says "It may be true, but that doesn't make it science. If nobody can see it, then nobody can replicate it. Which means we have no reason to believe it." He later goes on to suggest that the results be put up on an FTP site so that everybody could review the information and refute invalid hypotheses without having to take them to the presses first. It seems ridiculous to waste one's time with papers that have weak hypotheses based on a lack of access to data. It seems even more ridiculous to condemn these papers for having been written without better access to quality data when a lack of information sharing is a problem within the broader community. These papers are a product of environment. If we were to share access to quality data perhaps we could create more feasible theories concerning the evolutionary history of the hominid family.


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