Will the hobbit argument ever be resolved?
Debate over tiny human's evolutionary status is set to rage on.
For the past two years, researchers have been hotly debating (and coming dangerously close to fighting over) whether the fossils of a diminutive hominin found in Indonesia are those of a previously unknown species. The publication this week of some long-standing doubts over the 'hobbit' fossils show the debate is far from over.
The dispute over the bones of Homo floresiensis has involved allegations of name-calling, nationalistic motives, and wilfully damaging specimens. One camp insists that the tiny inhabitants of the Indonesian island of Flores were a unique species; the other claims that the bones are of a diseased Homo sapiens pygmy. As the debate rages, firstname.lastname@example.org set out to find whether there will ever be an end to the conflict.
The latest instalment came on Monday, with the publication in Proceedings of the National Academy of Sciences1 of doubts first raised by Indonesia's leading anthropologist, Teuku Jacob, of Gadjah Mada University, shortly after the finds were first published in 2004.
Jacob and his colleagues cite a range of evidence that the 'hobbit' bones bear similarities to features found in various modern pygmies, including a Rampasasa pygmy from Flores who has a receding chin (the single complete hobbit skull features a jaw with no chin at all).
Deformed by disease
The one complete hobbit skull found so far has additional 'deformities' not present in any modern Homo sapiens but these, Jacob's team argues, have been caused by disease. In their paper, they divide the iconic photograph of the hobbit skull down the middle and create mirror images of the two halves. The two halves look distinctly different evidence, the team argues, for developmental abnormality.
Peter Brown of the University of New England in Armidale, Australia, one of the team members who unveiled the findings in Nature2,3, retorts that this type of analysis is very prone to bias. "Depending on the camera angle you can produce anything you want from mirror imaging," says Brown. Particularly for a fossil that has been buried and squashed for thousands of years.
Accusations are also flying on both sides of bad conduct. Jacob has been accused of acting out of nationalistic pride and frustration at not having been the one to discover the bones. Meanwhile, authors of the new critique argue that this accusation is motivated by bitterness. "We have been introducing some scientific ideas and there has been quite a bit of name-calling in return," says Jacob's colleague Robert Eckhardt of Pennsylvania State University in University Park.
The bitter argument over different aspects of the bones' appearance begs the question of whether debates based on morphology will ever come to a definitive conclusion.
Brown remains convinced that definitive evidence of the hobbits' unique evolutionary provenance will emerge by studying further specimens: more skulls with the same features will make it more unlikely that the shape is caused by illness. "I think the issue will be resolved by fossils," says Brown.
The prospects for finding any more fossils look bleak, however. Political wranglings have led to a ban, for the time being, on excavations at Liang Bua, the cave where the hobbits were uncovered. Negotiations to reopen the site next year are ongoing.
Written in code
Some anthropologists have suggested that preserved DNA might provide a more definitive answer. If the Flores remains belong to H. sapiens, its DNA should fall within the range of modern human variation if it is a unique species, its DNA should be unlike anything seen in modern humans.
But excavation, cleaning and washing of the original specimens, done in part to harden and preserve them, almost certainly destroyed any DNA that might have been present. Attempts to obtain DNA samples (primarily from teeth, in which it should be best preserved) have so far been unsuccessful.
Brown's colleague Mike Morwood remains confident that, if more specimens can be found, they will yield DNA. "Given that DNA has been recovered from 8,000-year-old pig teeth from the site, there is an excellent chance of getting H. floresiensis DNA from future excavated remains," he says.
Brown is less hopeful, however. The hobbits are thought to have died out around 12,000 years ago, and although older DNA has been recovered from Neanderthals and mammoths in Europe, the damp, tropical Indonesian climate degrades DNA far more quickly. "It's a long way from ideal for preserving DNA," he says. "I would be surprised if DNA [from these samples] lasts even 2,000 years."
Probing the past
Dating the bones should provide more clues. Hominin tools have been found on Flores dating back to 880,000 years ago, leading Brown's team to speculate that the ancestors of H. floresiensis arrived then, surviving until perhaps 12,000 years ago (the various bones have been dated as 12,000 to 90,000 years old).
That comes with its own problems. "It is hard to see how the founding populations would have been large enough to survive for 40,000 generations," says Eckhardt. It is also difficult to imagine the population remaining unchallenged for that long, particularly as sea-level rises and falls to create land bridges between islands. Perhaps instead Homo erectus was responsible for the tools, and H. sapiens, arriving much later, for the Liang Bua bones.
But that pushes back the date of H. sapiens in Indonesia by quite a lot. H. sapiens is thought to have appeared in nearby Australia no more than 60,000 years ago.
Brown says an independent anthropological analysis soon to be published in the Journal of Human Evolution4 suggests that his story is correct: H. floresiensis is a unique species. Although he admits that the idea that the creatures developed their pygmy size while living on the island, as suggested in the original theory, may not be correct. "Now we think they arrived small."
Whatever the truth, the story of the Flores hominins is not over yet.
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- Jacob T., et al. Proc Natl Acad. Sci. USA, doi:10.1073/pnas.0605563103 (2006).
- Brown P., et al. Nature, 431. 1055 - 1061 (2004).
- Morwood M. J., et al. Nature, 431. 1087 - 1091 (2004).
- Argue D., Donlon D., Groves C.& Groves R. . J. Hum. Evol., doi:10.1016/j.jhevol.2006.04.013 (2006).
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