Homo floresiensis: the Hobbit

Homo floresiensis is a species of dwarf human discovered at the Liang Bua cave on the Indonesian island of Flores in 2003 (Brown et al. 2004, Morwood et al. 2004, Lahr and Foley 2004). H. floresienses was only about 1 meter in height and fully bipedal, with a very small brain size of 417cc. The skull has human-like teeth with a receding forehead and no chin. floresiensis fossils have been discovered from 38,000 to 18,000 years ago, though archeological evidence suggests it lived at Liang Bua between at least 95,000 and 13,000 years ago. It used stone tools and fire, and hunted pygmy elephants (mostly juvenile ones), Komodo dragons, and the giant rats found on Flores. Its discoverers believe that floresiensis is a dwarf form of Homo erectus - it is not uncommon for dwarf forms of large mammals to evolve on islands.
The most complete floresiensis fossil, LB1, consists of an almost complete skull and a partial skeleton consisting of leg bones, parts of the pelvis, hands and feet, and some other fragments. LB1 was an adult of about 30, probably female judging by the pelvis. Males could have been larger, though the other fossils found so far indicate only individuals about the same size as LB1. Because of the damp condition and young age, the bones of LB1 have not fossilized (i.e. had not turned to stone), and reportedly had the consistency of mashed potatoes.
The brain size of the floresiensis skull is extraordinarily small, at 380cc. This is as small as any australopithecine ever discovered, and fairly typical for a chimpanzee. (Chimps range from about 300 to 500cc, averaging about 400cc, but are physically bigger than floresiensis.) This is smaller than would be expected even for a dwarf form of Homo erectus, and suggests there was active selection for a small brain size for some reason. (Human pygmies, incidentally, are nothing like H. floresiensis; their brains are almost as large as those of normal-sized humans)
There has been some speculation that the stone tools found with it were actually made by Homo sapiens, mainly because it is hard to believe a creature with such a small brain could make such sophisticated stone tools. There is no other evidence in support of this, however, and if it were not for the small brain size, there would be no hesitation about assuming floresiensis made the tools because of the close association between the tools and the fossils. The same tools are found through the entire deposit (from 90,000 to 13,000 years ago) and, interestingly, they are not like any stone tools made by Homo erectus.

Skull of LB1 compared
with a modern human

Because evolving from erectus to floresiensis is such a drastic reduction in body size, there has been some speculation that floresiensis might actually have evolved from something smaller, such as the Dmanisi hominids found in Georgia, some of which have brain sizes between 600 and 700 cc, smaller than the 800-900cc typical of early erectus.
Flores was also in the news in 1998, when Mike Morwood (who is also involved with this new find) announced the discovery of stone tools at another site on Flores dated at 840,000 years. It was assumed at the time that this was evidence of Homo erectus, since erectus was the only pre-sapiens hominid known to have existed in Indonesia. Because Flores is thought to have always been separated from Java by a deep sea passage, this indicated a hitherto-unsuspected ability of H. erectus to cross sea barriers. The possibility now exists that the hominid responsible for this early archaeological evidence might not have been Homo erectus, but something else such as a Dmanisi hominid or a partly evolved form of floresiensis.
Modern humans arrived on Flores between 55,000 and 35,000 years ago, and presumably interacted with floresiensis, though there is no evidence of this at Liang Bua. However Indonesian folklore tells of creatures called Ebu Gogo which were small, inarticulate, and walked with an odd gait. This sounds remarkably suggestive of floresiensis, but it could easily be coincidence - if floresiensis had been found in Ireland, we'd possibly be wondering if they were leprechauns.
There is a possibility that DNA, particularly mitochondrial DNA (mtDNA), might be able to be retrieved from the bones. Their relatively recent age and the fact that the bones have not been been fossilized increases the likelihood that this can be done, but the tropical climate of Indonesia reduces the chance of success. High temperatures degrade DNA, and the Neandertal fossils from which mtDNA have been extracted all came from much colder climates than Indonesia. We will have to wait and see whether mtDNA can be successfully extracted from LB1. If so, it should prove very enlightening. (Some creationists are predicting that it will show floresiensis to be modern humans, but if, as Brown et al. believe, they descended from Homo erectus, the mtDNA of floresiensis should be even more different from modern humans than the Neandertals were.)
The discovery of H. floresiensis does not change the broad picture of human evolution, including our lineage - it was certainly not ancestral to us. But since it is the most extreme example of human adaptation ever found, it suggests that humans are more subject to evolutionary forces than we tend to think. And the fact that floresiensis lived so recently and yet has been unknown until now suggests that there could be other surprises waiting in the human family tree.

Other interpretations?

Anatomist Maciej Henneberg has claimed that the skull is extremely similar to that of a microcephalic specimen from Crete, microcephaly being a disease that causes small brain sizes. However, Peter Brown and his team have considered and rejected this explanation:

It's more difficult to rule out, I suppose, the analogy with abnormal modern humans, like pituitary dwarfs or microcephalic dwarfs, because there you can have small-bodied people who have small brain sizes as well. Very few of these people actually reach adulthood and they have a range of distinctive features, depending upon which particular syndrome they have, throughout the cranial vault and rest of the skeleton. None of these features are found in Liang Bua. It has a suite of clearly archaic traits which are replicated in a variety of early hominids and these archaic traits are not found in any abnormal humans which have ever been recorded. We now have the remains of 5 or 6 other individuals from the site, so it's not just one. There's a population of these things now and they all share the same features. (Peter Brown, in an interview with Scientific American)

Henneberg is a respected anatomist and his claim merits assessment by other scientists. However Brown is also an excellent anatomist, with the advantage of many months access to the fossils, and his paper was extensively peer-reviewed by other experts. Brown also claims that some of the other fossils, about which details are not yet public, support his interpretation, and several other researchers agree that LB1 is just too different to be a "peculiar modern human", in Chris Stringer's words (Balter 2004). Henneberg also claims that the size of the radius bone is consistent with an individual of 1.51-1.62 meters tall, considerably taller than LB1. This is in contrast to the discoverers, who have said that the size of the bone is consistent with the size of LB1 skeleton. This discrepancy will doubtless be thoroughly investigated.
Indonesia's most prominent paleoanthropologist Teuku Jacob has also been reported in newspapers as claiming that LB1 was not a member of a new species, but a member of the "Australomelanesid race" of modern humans, and only 1,300 to 1,800 years old.
March 2005: Falk and colleagues have published a paper (Falk et al. 2005) comparing a virtual endocast of LB1 with those from modern humans including a pygmy and a microcephalic, Homo erectus, some other fossils, and apes. Their results show that LB1 is quite unlike that of the microcephalic, and most like that of H. erectus, though this verdict is not accepted by Henneberg. (See further comments here)
October 2005: The discoverers of the hobbit have published a new paper (Morwood et al. 2005) describing more fossils, including some arm bones from the first hobbit skeleton, a second jaw bone, and many pieces from other individuals. According to them, and some other commentators, the new fossils confirm that the hobbit was a typical member of its population, and not an aberrant individual (in fact, some bones come from an individual smaller than the first hobbit).

Creationist responses

Given the massive media attention Homo floresiensis has received, creationists have naturally responded to it. Answers in Genesis has released two articles by Carl Wieland, Soggy dwarf bones and Hobbling the Hobbit, arguing that it is just a variety of modern human. ICR is more cautious, adopting a wait-and-see attitude. Some of the creationist articles refer to the criticisms of mainstream scientists such as Henneberg and Jacob mentioned above. Collectively, the articles are full of claims about how various aspects of the Homo floresiensis discovery cause problems for or are inconsistent with evolutionary theory. There are far too many of these to address individually, but none of them are remotely convincing. The most entertaining article is probably the Agape Press interview with Ken Ham, Creationism May Explain Skeletal Remains Better Than Darwinism. Ham is described as a 'science expert' (i.e. an ex-high school science teacher), and the creationist explanation for floresiensis turns out to consist of evolutionary mechanisms.
Many of the creationists seem to have a real problem with the stone tools found elsewhere on Flores and dated at 840,000 years. Both articles by Carl Wieland, the interview with Ken Ham, and the Harrub and Thompson article all claim the 840,000-year-old stone tools were found at the floresiensis site and pose a problem for evolutionists. Ham expresses this especially incoherently:

This creates a problem, the AIG spokesman says, "because then they dated the stone tools at 800,000 years. So they say maybe the tools were used by somebody else, and then these particular humans came later -- or something like that." Ham says evolutionists simply do not know what to do with this conflicting information.

This conflict is only in creationist imaginations, however. As the Morwood et al. (2004) paper clearly states, those stone tools were found at least 6 years ago at a different site about 50km away, and have nothing to do with the stone tools found at Liang Bua.
(See also my article at the Panda's Thumb about Answers in Genesis and floresiensis)

References

Balter M. (2004): Skeptics question whether Flores hominid is a new species. Science, 306:1116
Brown P., Sutikna T., Morwood M., Soejono R.P., Jatmiko, Saptomo E.W. et al. (2004): A new small-bodied hominin from the late Pleistocene of Flores, Indonesia. Nature, 431:1055-61.
Falk D., Hildebolt C., Smith K., Brown P., Jatmiko, Saptomo E.W. et al. (2005): The Brain of LB1, Homo floresiensis. Sciencexpress, 03 March 2005:1.
Lahr M.M. and Foley R. (2004): Human evolution writ small. Nature, 431:1043-4. (Commentary on Homo floresiensis)
Morwood M., Soejono R.P., Roberts R.G., Sutikna T., Turney C.S.M., Westaway K.E. et al. (2004): Archaeology and age of a new hominin from Flores in eastern Indonesia. Nature, 431:1087-91.
Morwood M. et al. (2005): Further evidence for small-bodied hominins from the Late Pleistocene of Flores, Indonesia. Nature, 437:1012-1017.

Links

Homo floresienses, from Wikipedia
Nature special on Flores Man
Mini Human Species Unearthed, by Scientific American
"Hobbit" Discovered: Tiny Human Ancestor Found in Asia, by National Geographic
Carl Zimmer's commentary on The Loom
Paul Myers' commentary on Pharyngula
John Hawks' weblog commentary on Flores

Creationist Links

Soggy dwarf bones, by Carl Wieland (Answers in Genesis)
Hobbling the hobbit?, by Carl Wieland (Answers in Genesis)
Yet another "rethinking" of "human evolution", by Frank Sherwin (Institute for Creation Research)
Creationism May Explain Skeletal Remains Better Than Darwinism, by Mary Rettig (Agape Press)
Eroding evolution's believability, by Kelly Hollowell (WorldNetDaily)
Hobbit Heresy, by Brad Harrub and Bert Thompson

In 2005