The Liang Bua debate, continued

References:

Vidal, John. 2005. "Bones of contention." The Guardian January 13, 2005. Guardian online

Wong, Kate. 2005. "The littlest human." Scientific American 292(2):56-65.

Two current articles examine the Flores questions from the metascientific angle. The first, from the Guardian includes this: "But every major find has a backlash, and in this case a fierce, high-level challenge has come from academics in several countries." The leader of the challenge is of course Teuku Jacob, who now supervises the fossils and has publicly claimed that they may represent a dwarf, and certainly belong to our own species. This article also contains more fresh material to digest, concerning the present status of the remains and the debate emerging from them.

Kate Wong's article in Scientific American is perhaps the best summary of what has been found and the hypotheses presented to date. I suggest it strongly to anyone wanting to get up to date. It includes a great background to the discovery from the perspective of the Australians (although not the Indonesians who actually did the finding, who haven't been interviewed by anyone that I've seen). The most interesting new thrust to the research covered here is the speculation about the brain and intelligence, discussed below.

The Jacob angle

The piece in the Guardian reads as a defense of Jacob, and he deserves one after the media treatment he has received to date. Here is one detail:

But he is keeping the latest Flores find in a safe in his steel-doored vault. Like all other major finds made by the department of archaeology, the bones were sent to his laboratory. He did not - as the press have said - kidnap them. "They even gave me the money for the transport."

According to this article, Jacob has arrived at the view that LB 1 is a microcephalic pygmy. This conclusion is supported by the observation that pygmies are common in the region today, may have been more common in the past, and the possibly high frequency of secondary microcephaly, induced by nutritional deficiency or other non-genetic factors. The article also cites Alan Thorne on this idea. Also, Jacob believes the skeleton to be male, leading to an impression of robusticity in its small size that may mislead toward an identification with archaic humans.

The ebu gogo angle

Both the stories feature the presence of a local myth about small hairy creatures that live in the forest and shy away from human contact. The creature is called ebu gogo, translated as "the grandmother who eats anything" (Wong 2004:58). This has clearly become the sensationalist perspective on the story: the hint that sometime in the recent past the ancient H. floresiensis population still existed and that historic peoples encountered it.

It's certainly a colorful way to start an article, and both use it mostly for flavor. The Vidal article does create an interesting dualism between the local myths of the small creatures and the current presence of some very small people, with the latter symbolizing the idea of an extinct species and the former representing the possibility of genetic input from the ancient people into the living population of Flores. Of greater concern is the cryptozoological bent behind the idea that some small number of the tiny hominids might still be there to be discovered in some Floresian forest.

The multiregionalist angle

In the Guardian article, Richard "Bert" Roberts is quoted as saying this about the critics of the H. floresiensis idea: "All ... are supporters of the multiregionalism evolutionary model ... This discovery would destroy their theory. It suits their purposes very nicely [to oppose Homo floresiensis]."

Is it true? Is this a conspiracy of multiregionalists bent on defending their theory? It certainly is true that Maciej Henneberg and Alan Thorne have written supportively of multiregional evolution. But then so have I, and I'm not part of a cabal bent on discrediting pygmy hominids. I think there may be a certain skeptical frame of mind that connects different theories in this way: as for myself, I am pretty skeptical of about anything. Part of that skepticism is directed toward genetic arguments for Out of Africa, and that certainly trends me toward multiregional evolution. But a broader part is directed toward almost every simple answer, which is a great aid to my work.

Does the existence of Homo floresiensis discredit multiregional evolution? As far as I can see, there is little relationship between the two. Suppose that an isolated population of humans existed on an island for large parts of the Pleistocene, never contacted populations elsewhere until protohistoric times, and had become a distinct species. What about that would suggest that other human populations had become reproductively isolated, failed to interact with each other across continental landmasses instead of permanently isolated islands, and thus became multiple hominid species?

Now there is a very indirect argument to be made, which is that one case of a distinct hominid lineage within the last two million years increases the prior probability of other distinct lineages within that timeframe. In other words, H. floresiensis does not serve as direct evidence against multiregional evolution, but it does tend to increase our reasons to think that another hypothesis might be right. I think that considering the uniqueness of the situation on Flores, that this argument is far too indirect to have any relevance to the multiregional vs. Out of Africa debate. Or more correctly, it has exactly the same relevance as every other signpost along the bush vs. ladder continuum, which is pretty much zero.

The only morphological evidence that has relevance is evidence of gene flow among human groups at certain times. If Teuku Jacob is to be believed, the LB 1 skull has features that align it with recent Indonesian peoples. If this is true, then clearly the most likely hypothesis is that the skeleton simply is a modern human with an unusually small body and brain size. Now, this wouldn't be strong support for multiregional evolution, since the skeleton is only 18,000 years old and therefore significantly postdates the movement of modern humans into the region.

But then, this is one of the underappreciated aspects of the story: by 18,000 years ago modern humans were in the region sailing among the islands of the Indonesian archipelago, to Australia and New Guinea, and to further out island Melanesia, the Philipines, and Okinawa. In other words, maritime technology had made possible the colonization of islands out of sight of each other over significant ocean crossings, and this technology had been sustained since at least 30,000 years ago and very possibly as early as the habitation of Australia. In this context, it seems certain that the archaeological remains in the cave were left by modern humans. The only remaining question is whether the fossil remains were themselves modern or instead represent a different extinct species.

What about the brain?

The Scientific American article goes into more detail about the small brain problem than any other published account. The main question is whether a small brain--remember, the smallest known for any hominid--is capable of producing the material culture recovered from Liang Bua. The article has informative quotes from several people, some think that it's impossible for H. floresiensis to have made the tools (Richard Klein), others think it's a question of brain organization instead of brain size (Richard Potts).

It is important to separate the brain size issue from the species issue when talking about behavioral capacities. For example, applying the example of the smart humans with small brain volumes is a good reminder of why brain size isn't everything, but that reminder is applicable only within our own species. The fact that some modern people behave normally, or even exceptionally, despite having very small brains is possible because they are humans and operate within the context of human culture. If LB 1 was a modern human with microcephaly, this example should clearly apply--the individual himself (or herself) may well have been capable of tool manufacture and other foraging-related cognitive tasks in addition to social participation, because his or her survival in a modern human population would be impossible without mastering relatively challenging cognitive social interactions.

But just because some modern humans behave in complex ways using only the brain size of an early hominid does not mean that early hominids could interact in ways like modern humans. For ancient human populations, we may assume little or nothing about cultural systems and the ways they may have influenced cognition. It is certainly unlikely that a population of small-brained hominids could have developed cognitive skills equal to modern humans without corresponding increases in the size of the brain. Presumably these hominids would have been under selection for cognitive skills. Thus, for these skills to increase without a corresponding increase in the size of the brain would require that the skills be uncorrelated with the size of the brain. We know little about the genetic basis of cognitive traits, and less about those traits that are of empirical interest for the Flores hominids, such as tool manufacture and Stegodon hunting. But intelligence is strongly correlated with brain size within living human populations, despite the existence of very smart small-brained people in all populations.

Thus, although brain size is not destiny for the individual, for the population it serves as a fairly potent marker of evolutionary forces acting to increase cognition. If LB 1 was representative of a small-bodied, small-brained population, we can say with confidence that it was not a tool-using hominid.

More on the Flores hominids