Questions still abound about the ancestry of Homo Floresiensis or "The Hobbit" discovered on Flores Island. Is it a descendant of Homo erectus or of Australopithecus or is it something entirely new?
The beguiling questions concerning Homo floresiensis are the matter of encephalization or brain size and skull shape. These factors make classification of this new species very complicated. Is it a dwarf Homo erectus, or a pathological Homo sapien, or could it even be an Australopithecine. I will discuss the pros and cons of each of these interpretations.
Could this extraordinary creature originally dubbed “The hobbit” be a long lost Australopithecine? One of the features it has in common with Australopithecine is overall size. It is actually a bit smaller than its three million year old cousin. The femur length of Homo floresiensis plotted against the log of the endocranial volume shows Homo floresiensis to be the smallest of all the hominids that appear in the fossil record (Brown 2004). This might suggest an Australopithecine to some, but the timing suggests a spurious correlation.
First of all, the dates are all wrong. H. floresiensis has dates as recent as 18,000 years ago (Lahr and Foley, 2004). This is way out of sync with the classic Australopithecine dates which goes all the way back to circa 3 million years ago. That would make H. floresiensis anachronistic in the extreme. That is to say Australopithecines did not die out 3 million years ago but they have been running around ever since and somehow made their way to Indonesia.
Figure 1. Occlusal view of LB1 mandible (Brown, 2004).
Figure 2. Comparitive mandibles of Chimpanzee, Australopithacine, and Human
Figure 3. Lucy’s Jaw (Australopithecine afarensis) (Johanson, 1981)
Which brings up my second point, Australopithecines have only ever been found in Africa. There is not a single Australopithecine fossil anywhere else in the world. This means that H. floresiensis would have left no other fossils behind as it migrated from Africa to Indonesia over a three million year period. Most experts agree that a three million year gap in the fossil record is highly unlikely and unprecedented.
Lastly, the allometry is all wrong. Allometry is the science of the measurements of the bones of, and the brain case size of the cranium. All the experts agree that the overall appearance of the H. floresiensis skull is that of a miniature Homo Erectus. Looking at the mandible comparison I have provided one can see that, when looking at figures 1 and 3, the H. floresiensis mandible in figure 1 has the classic human “Arch” shape whereas the Australopithecine mandible (from Lucy) in figure 3 has a much more primitive “V” shape. Figure 2 shows a Chimpanzee, with the classic ape “U” shape as compared with Australopithecine (“V” shape) and a modern Homo sapien sapien mandible (“Arch” shaped). Remember you are looking at the pattern the teeth make not the jaw bone itself.
This clearly demonstrates that H. floresiensis belongs solidly in the range of Homo and is not an Australopithecine.
Next follows the question; could H. floresiensis be a pathological or dwarf Homo sapien? This could prove to be a harder question to answer. There is no medical precedence for any human aberration, dwarf or otherwise having such a small brain size. Brain size to body weight ration is a consistant measurement troughout the fossil record and animal kingdom and is an excellent qualifier for measuring problem soliving skills of any of the Anthropoids. At 340cc Homo floresiensis has the smallest brain size by far. Smaller even than chimpanzees. Human brains are between 1450cc to 1550cc’s. Human dwarf’s brain size still falls within this range so it seems unlikely that this would be some kind of aberration that took hold and evolved a little person with a fifth of the brain size. We just do not see this anywhere in nature.
As far as the question of whether this is pathology or not, it would have to be an extreme pathological problem. This idea, though it fits the facts better than the Australopithecine model, is still counter intuitive. To be born, grow old and die with that kind of aberration would be tough to do indeed. That is not to say that it isn’t possible but it seems highly unlikely. That kind of aberration would select itself right out of the gene pool very quickly. A human born with a brain size to body weight ratio fitting the measurments of H. floresiensis could not survive today much less 18,000 years ago. No, it seems there must be another explanation.
It seems the term dwarf Homo erectus may not be the most apt, but of the given choices, the most applicable. The facial structure is prognathic just the way H. erectus is. The time periods make much more sense. H. floresiensis would have been contemporaneous with Homo neanderthals and H. sapiens. This overlap of species is precedented all the way through the human evolution. We also know that H. erectus in which ever form, made it at least as far as Trinil, Java. With just a little help and luck (and maybe a raft or two) H. erectus could have made it to the islands of Indonesia, perhaps all the way to Flores.
As for the size difference, an environmental explanation of size reduction is most likely. What causes this dwarfing (for lack of a better term) is a bit of a mystery but to think that H. erectus would be immune is not a very scientific attitude. Smaller area of existence, limited food and resources, surrounded by water, a smaller frame and less expensive tissue would be an adaptive evolutionary change to those kinds of conditions. But the brain size is still a quandary. There are two examples in extant species that jump to mind that show this kind of environmental miniaturization. In Africa the Genus Loxodonta, or elephants is recently divided into two species, africanus, the savannah dwelling elephants and cyclotis or forest elephant. They used to be considered the same elephant even givin their physical dissimilarity. The plains elephants are much larger than the forest elephants and this is direct result of the environmental pressures of their given habitats. Even more telling is the difference in variability of the human speies in the same region. The Masai peoples of Africa live in the grasslands and are very tall ( 6-7 ft typically), yet they are genetically viable with the Pygmy or Forest peoples, who are very small of stature (3-4ft typically) and they live in the same equatorial longitudes. When one investigates further examples of forest and island dwelling species that are the same are found to maintain this size variation.
Finding a species like Homo floresiensis does not change dramatically the way we think about human evolution, it expands our understanding of not only the fact that there are more and varied species than we previously thought but that we will continue to find startling variations the longer we dig in the dirt of caves. It belongs in the genus Homo as much as anything else does. We have to keep in mind that the Genus Homo is our own construct and not as factual as we would like. One of the most prevalent problems with the science of human evolution is that we create categories of our own design the get frustrated when new discoveries do not fit nicely into those arbitrary constructs. Homo floresiensis is a unique and important discovery that broadens our base of knowledge and it will be argued about for many years to come.