On My Fossil Wish List: Homo sulawesiensis

i-a22ac2052a1e0cb8978dd050d9866768-head pop crop.jpg

Could 2007 see some new hobbits? I certainly hope so.

In October 2004, a team of scientists announced they had found bones of a hominid from the Indonesian island of Flores. They came to the astonishing conclusion that the bones belonged to a new species, which they called Homo floresiensis, which stood only three feet tall, lived as recently as 12,000 years ago, had a chimp-sized brain, and could use stone tools to hunt.

That announcement launched an extraordinary debate, with scientists arguing in favor of tiny hominids (nicknamed Hobbits), or a dwarf with a birth defect, or an unusually evolved population of humans. For a timeline, see this post I wrote in this past October, surveying two years of controversy.

i-c554df96a4f21e670b7b9115e540b7ef-new hobbit.jpgIt's been a quiet winter on the H. floresiensis front, but for some odd reason a few pieces of intriguing news have come up in just the past couple days.

In the Proceedings of the National Academy of Sciences, a team of scientists led by Dean Falk of Florida State look once more at the shape of H. floresiensis's brain and compare it to the brains of humans. One major objection to the idea that the hobbits are a separate species comes from critics who claim its small skull could have been caused by a genetic defect known as microcephaly. In 2005 Dean Falk and co. recreated the hobbit's braincase from one fossil and then compared it to, among other things, a human microcephalic brain case. At the time they concluded it had a distinctive shape not seen in microcephalics.

Critics then responded with a lot more microcephalic skulls and the argument that microcephaly can take a staggeringly wide range of possible shapes. And some of the microcephalics they found seemed to have hobbity braincases.

So now comes the new paper from Falk. In it, she and her colleagues compare nine microcephalic brains and a dozen normal human ones. (The picture above shows a reconstruction of one microcephalic on the left and Homo floresiensis on the right.) The scientists identified some key traits that they could use to classify brains as normal or microcephalic with complete accuracy. Although microcephalics do vary a lot in some ways, the researchers found that their cerebellum (a lump in the back of the brain important for motor control) protrudes and bulges a lot compared to a normal cerebellum. They also have narrow, flattened orbital lobes. According to this standard, Homo floresiensis is not a microcephalic. (The paper is not online yet, but when it goes up, this link will work: http://www.pnas.org/cgi/doi/10.1073/pnas.0609185104)

Robert Martin of the Field Museum, one of the biggest critics, is not buying it. This National Geograpic article has a bit of back-and-forth between him and Falk on the finer details of how to measure brains properly. Richard Potts of the Smithsonian is quoted telling all these scientists to "step outside the black box of the brain they've gotten themselves into."

It is certainly striking how so much of the debate has revolved around the brain of Homo floresiensis, and how all of the information scientists have about its brain comes from a single fossil. Scientists have indeed found other bones from the same cave from different ages, such as a jaw and limb fragments, but they've attracted much less attention. There could be, in theory, so many other sources of information, from the skulls of other individuals to more limb bones to DNA.

But prospects for this other kind of information have seemed very bleak. A conflict between researchers ultimately led to the Indonesian government closing off the cave where the fossils were found in 2005. In a December feature on Homo floresiensis in the journal PLOS Biology, Tabitha Powledge reported that attempts to get DNA from the bone had failed. The world was left to gaze at the single braincase like an inscrutable Eight Ball.

Now there seems to be some cause for hope. Potts, for example, hints in the NG article that there will be new studies coming out on other parts of Homo floresiensis that will support Falk. And the team of Australian and Indonesian scientists who originally found Homo floresiensis have been doing some more work on the material they got from the cave. As the Sydney Morning Herald reports, they suspect that modern humans wiped out the hobbits.

Bones ascribed to hobbits range from 95,000 to 12,000 years ago. Younger cave deposits include modern human bones. A layer of ash lies on top of the most recent hobbit bones, which prompted the scientists to suggest that a devastating volcanic eruption wiped out Homo floresiensis, and modern humans later colonized a hobbit-free island. But now, according to the Herald, it appears that the eruption took place about 600 kilometers to the west. At that distance, the volcano probably didn't wipe out life on Flores. So perhaps modern humans arrived on Flores and quickly drove the hobbits extinct. One possibility is that they hunted the pygmy elephants on which the hobbits may have lived. (It doesn't appear that the results are published yet.)

But the biggests ray of hope comes from the fact that the cave is now open for business again. The details of the negotiations are vague, but the scientists are set to be back in the cave this spring. I was particularly struck by Mike Morwood's comment to the Herald that researchers will also be heading for the nearby island of Sulawesi, a much bigger land mass that's also much closer to southeast Asia, from which the ancestors of Homo floresiensis came.

This island was the most likely source of the hobbits' ancestors. "My guess is that hominids arrived on Sulawesi a long time before a small group were somehow washed out to sea, to be deposited on Flores," he said. "It is now the place with real potential to surprise."

To discover a chain of hominid species stretching from the mainland out to Flores would be cool beyond belief. When did the dwarfing begin, one wonders? Was there a Homo sulawesiensis before a Homo floresiensis? Or were the only hominids exploring these tropical islands members of our own species? Here's hoping 2007 provides some answers.

[Image: Kirk E. Smith, Electronic Radiology Laboratory, Mallinckrodt Institute of Radiology]

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From the Reuter's story (via Yahoo):

Martin remained unconvinced. "My gut feeling is what they (Falk's team) did is just played around with the measurements until they got something that suited them," Martin said.

Rather nasty comment, I would say, bordering on accusation of fraud. No evidence either, just his 'gut feeling.'

I would have been much happier if the people who simply asserted that measured bone asymmetries are due to burial distortion accounted for each of these measurements from their model if possible. That is still an open issue AFAIK, and as I understand it a stronger indicator of pathology.

The newfound chamber in the back is exciting though, considering the better conditions for the bones and its seeming use for waste. ( http://scienceblogs.com/afarensis/2007/01/29/homo_floresiensis_the_cham… )

By Torbjörn Larsson (not verified) on 30 Jan 2007 #permalink

Ray, unfortunately that's the nature of paleoanthropology and osteology and generally any scientific field based on qualitative phenotypic analysis. One person's basis may influence the ways they choose to measure and gather data and ultimate affect the conclusions they make.

Despite that, it seems like Falk has done her best to compare nearly a dozen microcephalic H. sapiens to Flores. While that sample size is a bit small, I indicated in my blog, that's probably due to the limiations on microcephalic skulls available to measure. So long as she and her team was consistent in measurements, say from key landmarks within the cranial cavity, the statistical significance should be a sound conclusion.

However, I should say I haven't gotten a copy of the article yet and I've been somewhat skeptical of Flores as a separate species... but this seems like a strong study.

Not being an expert in this field, I hesitate to make a firm judgment on the debate. But after reading the recently published Morwood/ van der Zee book, I still can't see how the sceptics will explain the existence of the other post-cranial remains, which all seem just the same - or at least very similar - to the main "Hobbit" skeleton. One microcephalic is (just) possible, but a whole race of them strains credibility.

Yes, homo sulawesiensis is an attractive prospect, and it may well exist. In the book, Morwood/vd Zee explain that the research which led to the Hobbit discovery is part of a wider effort to establish when hominids first arrived in Indonesia, where they came from, etc. They have some detail about ocean currents which might indicate how species spread around the archipelago, and the greatest likelihood for the point of origin of the Hobbits is Sulawesi, where very little excavation has been done to date.

But two words of warning are in order. Firstly, there has been much trouble and violence in certain parts of Sulawesi in recent years, and permits for research may not be easy to obtain, especially if interesting sites are anywhere near politically unstable areas (I don't know if they are).

The second point arises from an interesting exchange recorded in the book - Morwood recounts that after the Indonesian Institute of Science (LIPI) got into the act, one of his Indonesian associates told him that the bureaucratic objections had arisen because the research had been "too successful". He didn't explain what this meant, but Indonesian bureacracy is full of controversy, jealousy and rivalries (so it's not unique!), but lying behind this, I imagine, is the considerable Indonesian sensitivity about anything to do with evolution, especially hominid evolution. The hobbit discovery exposed issues of human origins and publicised scientific explanations of these issues which many Indonesians would rather not know about. This is separate from, but connected to, the antics of people like Teuku Jacob, who I suspect is himself a Muslim creationist.

By John Monfries (not verified) on 31 Jan 2007 #permalink

"My gut feeling is what they (Falk's team) did is just played around with the measurements until they got something that suited them,"

A nice replication study would be for someone to develop a set of criteria like those identified by Falk et al but without access or reference to H.F.

While Ray is right to observe that this accusation of cherry-picking is harsh, such actions are certainly not unheard-of. It could even be unintentional: Falk certainly has a lot invested in the Hobbit Hypothesis and he and his team will presumably have been working with a great knowledge of the H.F. skull. A medical trial (or suchlike) performed this way ithout blinding would certainly be open to criticism, and while I would not impugn Falk it's certainly worthy of blinded replication.

Ignorant but genuine question: why would H. sulawesiensis* not be H. erectus (or H. sapiens)?

My limited understanding of the mechanisms of insular dwarfism is that you'd need a much smaller landmass than Sulawesi to trigger the effect. Is that wrong? Of course any hominid on Sulawesi might well be ancestral to the Flores population, but why would it be particularly special in itself?

Chris--A population of Homo erectus that wound up on Sulawesi could have evolved into a separate species without dwarfing. If they became distinct enough from mainland Homo erectus in other ways, they could warrant their own species. The dwarfing might not have occurred until a population moved from Sulawesi to Flores.

Of course, there are lots of other possibilities.

Homo Sulawesiensis?

I'm holding out for a return of Piltdown Man.
At least Piltdown was what we were expecting at the time.

As far as i know from the literature, only Tolkien expected hobbits.

The best thing to happen would be either more skull fossils or better means of extracting DNA from fossils which seems to be under development.

As an aside, between the unusual behavior of the Indonesian anthropologist in this case and what I heard recently about Indonesia trying to assert "intellectual property rights" over a strain of H5N1 virus, I am getting the idea that Indonesia has an "interesting" perspective on the process of science. I have nothing against a nation trying to get the most from its efforts but the bogarting of fossils and the sniping of vaccine technology which could save millions seems kind of petty to me.

A few points.

Tolkien's hobbits were his adaptation of English fairy tale hobbits (aka hobs and bobgoblins) of his day. The Flores Island hobbits got that name thanks to certain researchers' playfulness.

I rather doubt Homo floresiensis is descended from Homo erectus, because H. Foresiensis has skeletal features found in Australopithecines and H. Habilis, but not H. erectus. I consider it more likely that H. floresiensis inherited those features from H. georgicus; an animal also touted as an ancestor of H. erectus through a separate line of descendent. It's more likely that populations of H. georgicus arrived in Indonesia still at the original 4 feet in height; thus the reduction to around 3 feet in height wouldn't be that much of a ... stretch.

To Alan Kellogg
Tolkien's hobbits actually bear little relationship to any conventional fairy-tale creatures. The word 'hobbit', as a word, might have cropped up in some early bestiary, but in the context of many other things. Tolkien's own experience of writing about hobbits was that they just popped into his head, and he wrote about them. If Tolkien's creatures have literary antecedents, it is with the Snergs, from a children's story called The Marvelous Land of Snergs, by E. A. Wyke-Smith -- Tolkien certainly knew of this and acknoweldged the debt. A deeper analysis shows that the lack of any link between hobbits and traditional fairy-tale creatures (elves, dwarves, goblins etc) was entirely deliberate, as it is part of the function of hobbits on Middle-earth to be anachronistic. Tom Shippey discusses this in his book The Road To Middle-Earth.

By Henry Gee (not verified) on 13 Feb 2007 #permalink

Aw, shucks, Carl, you rumbled me.

But to return to the business in hand, I think that further discoveries of tiny hominids either at Liang Bua, or, even better, elsewhere in Indonesia, will be the only way that the doubters will be silenced. At the moment, the Flores-as-pathology school conveniently ignores the time depth at Liang Bua. There is more than just the skull LB1 -- there is another jaw, and quite a few other bones, dating from around 14,000 to as much as 95,000 years old. More material from other sites will help address the pathology idea.

Interestingly, radical discoveries of new hominids are conventionally met with disbelief of the kind which Dawkins has labelled the 'Argument from Incredulity' (that is, 'I don't believe it, so it can't be true') and Flores doesn't seem tp be immune from this.

This happened when Australopithecus africanus was announced by Raymond Dart in the 1920s, from a single specimen -- the skull from Taung in S Africa. The By the same token, when Neanderthals were first discovered, the experts thought they were pathological humans (sound familiar?)

In the case of A. africanus, doubts were dispelled when Broom came in to support Dart and found all sorts of Australopithecines at other sites in South Africa such as Kromdraai.

By Henry Gee (not verified) on 15 Feb 2007 #permalink

Hmmm, small brain, small size, odd molars but parabolic dental arch, small canines, chinless, toolmaking...does the name Raymong Dart come to mind?

By aragonite (not verified) on 21 Mar 2007 #permalink