Tuesday, May 5, 2009

Hobbit hunters

Even before I watched the Nova episode entitled "Alien from Earth," I had been thinking about writing a post about the discovery of prehistoric "hobbit" bones in Indonesia. Who were these hobbits? Are they really members of new species? Nova presented a good case for new species status, as well as making some intriguing suggestions about what this may tell us about human evolution. Here's the story as I now see it...




Homo floresiensis

In 2003, paleoanthropologists were looking for evidence on early man's migration from East Asia to Australia when they made a surprising discovery. In the Liang Bua cave on the Indonesian island of Flores, they uncovered the remains of several hominids including one near complete skeleton with a complete skull. At first, they assumed these bones belonged to a child as it would have only stood about 3' tall, but they soon realized this was an adult woman around 30 years old. She was about the size of the average three-year-old, but her skull was even smaller: like the size of a grapefruit. Because of its uniquely small stature, the discoverers hypothesized that this was a new species which they dubbed Homo floresiensis and which has been widely nicknamed "the hobbit" in the scientific community and the press.

Near these hobbit bones, scientists also found the remnants of what looked to be fairly advanced stone tools as well as charred bones belonging to the pygmy elephants which once roamed the island. Not only that, but the youngest set of bones was dated to around 18,000 years ago – at least 5,000 years younger than the latest Neanderthal remains; this means that hobbits would have existed well into the age of modern man.

A New Species?

Since the bones were unearthed, many scientists have disputed the discoverers' new species claim and advanced less radical explanations for the hobbits' unusual size. It's been suggested that these could just be modern human pygmies. But no modern pygmies are even close to this tiny, and what about the hobbit's small brain which is closer in size to that of a chimpanzee or australopithecene (very early hominid, like Lucy) than that of a modern human?

Another theory is that the main hobbit skeleton belonged to a modern human suffering from some sort of disease. Specifically, a lot of scientists have suggested that she was microcephalic. Microcephaly is a disorder in which the brain and cranium do not grow to normal size: microcephalics are usually mentally retarded, and the disorder is also associated with dwarfism. Could our hobbit have been a microcephalic pygmy?

This theory had been espoused by many anthropologists who rejected the new species claim, but in 2007 a new study was published which seems to definitively rule out this possibility. American scientists compared a 3D computer generated model of the hobbit's brain with that of 9 contemporary microcephalics. They found that, although the hobbit's brain was similar in size, its features were wholly dissimilar to that of microcephalic humans.

Other anatomical studies of the hobbit bones have added further weight to the theory that these were not modern humans. An examination of the bones in the hobbit's wrist show that they are more akin to those of chimpanzees and australopithecene than to those of Homo sapiens. Another study looked at the hobbits' teeth (in addition to the female skull there was also another jaw bone found). The study found that these sets of teeth were similar to one another and yet very different from those of modern humans. Thus, either the two specimens (which were dated over a thousand years apart) are Homo sapiens that both shared the same rare condition, or perhaps they are not human and their teeth are typical of their species.

All this evidence seems to point in the direction of the hobbit being a new species of primitive hominid, but seeing as how we only have one fairly complete skeleton and some other assorted bones (although, hey, the fossil record for a lot of other hominid species is even more fragmentary) we'll have to wait for more physical specimens before we can say for sure. One of the priorities of scientists as they continue excavation work on Flores is to try to recover fossils which preserve Homo floresiensis DNA so that it can be compared to that of other species.

What were the hobbits like?

The discovery of the hobbits presents a bit of a paradox: the hominids' small cranial capacity and other anatomical characteristics seem to indicate it was a sort of throwback to the earliest human ancestors and to apes, but at the same time their remains were found near stone tools. Some scientists say that these tools don't look all that different from those developed by australopithecene in East Africa (Developed Oldowan tools). But there's also evidence that these might be the type of more advanced tools usually associated with modern man (there's some evidence suggesting wood working and use of bamboo).

And what about the scorched stegodon bones? Not only do they suggest that the hobbits knew how to build fires, but in order for these toddler-sized hominids to take down a pygmy elephant (around the size of a large cow and weighing as much as a Mini Cooper) they would have had to hunt in groups. This would imply sophisticated social skills and communication, maybe even (most controversially) some sort of language.

Thus, some scientists theorize that the hobbits were more intelligent than their diminutive brains suggest. And this may well be because, although the hobbit brain is smaller than that of Homo sapiens or Homo erectus, some of its features are associated with higher thought processes.

Where did the hobbits come from?

This is perhaps the biggest question. If Homo floresiensis is indeed a new species, distinct from Homo sapiens, then what species did it evolve from? When did its evolutionary path diverge from that of modern man? The neatest explanation would be that it evolved from Homo erectus, a species that is closely related to Homo sapiens if not a direct ancestor and which is usually identified as the first hominid to migrate out of Africa. If this were the case then perhaps the hobbits' smaller size can be attributed to island dwarfism: populations of mammals isolated on islands often evolve to be unusually small in size (like those pygmy elephants) or unusally large in size (like the komodo dragon, which is a giant monitor lizard).

On the Nova documentary, a scientist from the Flores excavation team rejects this hypothesis stating that there is no evidence of island dwarfism ever resulting in diminished cranial capacity in humans. Homo floresiensis' small stature and brain size and primitive proportions all seem to point further back in the evolutionary chain, so maybe the hobbits' unique evolutionary path started even earlier.

The suggestion that Homo erectus was not the first hominid to leave Africa is controversial, but the Nova documentary mentioned the discovery of Homo georgicus, to date the earliest fossil found outside Africa, in Dmanisi, Georgia which is thought to represent an intermediate step between Homo habilus and Homo erectus. Moreover, on the Nova website, Michael Morwood, one of the leaders of the team that discovered the hobbit, mentions recent evidence of remains found on the isle of Java which may be more primitive than Homo erectus (Meganthropus).

At another interesting site on the isle of Flores, called Mata Menge, scientists have found stone tools similar to those found in Liang Bua which date back 880,000 years. It's hypothesized that whoever created these tools (Homo erectus? They're too old to be the work of modern man) may be the ancestors of our hobbits.

Conclusions

It's amazing to think that the diminutive hominids found on the isle of Flores might belong to a new, fairly intelligent race whose evolution diverged from our own over a million years ago. Likewise, they may have developed there in relative isolation over the course of over 800,000 years. We'll need to find a lot more evidence before we can have any certainty about the origins of the hobbit, but one thing is certain: coupled with other recent findings such as Homo georgicus and Meganthropus, Homo floresiensis suggests that the human evolutionary family tree may have more branches and be much richer and more complex than we assumed up until now.

And when did the hobbits die out? Some scientists think they may have been killed off around 13,000 years ago by the same volcanic eruption that finished off their prey, the island's pygmy elephants.


For the answers to more questions regarding the hobbit I would direct you to the Q&A with Dr. Michael Morwood on Nova's website.


Images: cast of Homo floresiensis skull found in New York's American Museum of Natural History; photo Homo floresiensis fossil jaws by Djune Ivereigh/ARKUNAS found on Turkana Basin Institute's webpage on the hobbit.

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