Monday, November 08, 2004

A Headache for Paleoanthropologists?

Today's New York Times provides this follow-up article suggesting that various bits of palontological wisdom will have to be rethought in light of the discovery:

The miniature people found to have lived on the Indonesian island of Flores until 13,000 years ago may well appeal to the imagination. Even their Australian discoverers refer to them with fanciful names. But the little Floresians have created something of a headache for paleoanthropologists.

The Floresians, whose existence was reported late last month, have shaken up existing views of the human past for three reasons: they are so recent, so small and apparently so smart. None of these findings fits easily into current accounts of human evolution.

The article is interesting, but a bit too sensational for my taste. For example, it goes on to explain:

The textbooks describe an increase in human brain size that parallels an increasing sophistication in stone tools. Our close cousins the chimpanzees have brains one third the size of ours, as do the Australopithecines, the apelike human ancestors who evolved after the split from the joint human-chimp ancestor six or seven million years ago. But the Australopithecines left no stone tools, and chimps, though they use natural stones to smash things, have no comprehension of fashioning a stone for a specific task.

The little Floresians seem to have made sophisticated stone tools yet did so with brains of 380 cubic centimeters, about the same size as the chimp and Australopithecine brains. This is a thumb in the eye for the tidy textbook explanations that link sophisticated technology with increasing human brain size.

Perhaps. On the other hand, while H. floresiensis may have had brains the size of chmipanzees they apparently had bodies that were much smaller. (Roughly 25 kg according to the article cited in the previous post as compared with 35-70 kg, according to this interesting site about chimpanzees). As everyone knows, brain size by itself is not a reliable indicator of intelligence. The ratio of brain size to body size is a far better measure, and on that scale our little friends fare reasonably well.

The most interesting part of the article deals with speculations about whether H. floresiensis is more closely related to H. erectus or H. sapiens (that's us!) Personally, I'm rooting for the H. sapiens just because I like the idea of human beings speciating. Here's what the article has to say about it:

There has been little evidence until now that Homo erectus long survived its younger cousins' arrival in the region. Modern humans probably exterminated the world's other archaic humans, the Neanderthals in Europe. Yet the little Floresians survived some 30,000 years into modern times, the only archaic human species known to have done so.

All these surprises raise an alternative explanation. What if the Floresians are descended from modern humans, not from Homo erectus?

“I think the issue of whether it derives from H. erectus or H. sapiens is difficult or impossible to answer on the morphology,” says Dr. Richard Klein, an archaeologist at Stanford. And if the individual described in the Nature articles indeed made the sophisticated tools found in the same cave, “then it is more likely to be H. sapiens,” he says.

The same possibility has been raised by two anthropologists at the University of Cambridge, Dr. Marta Miraz√≥n Lahr and Dr. Robert Foley. Commenting on the sophisticated stone implements found in the cave with the Floresians, they write that “their contrast with tools found anywhere with H. erectus is very striking.”

There is the basis here for a fierce dispute. Given what is on the record so far, the argument that the Floresians are descended from Homo sapiens, not erectus, has a certain parsimony. Moderns are known to have been around in the general area, and no Homo erectus is known to have made such sophisticated tools.

The article goes on to provide some possible counters to these arguments.

One of the great frustrations of paleontology is that nature only provides us with so many fossils and there is only so much information that can be extracted from them. This is precisely why theories regarding the specific trajectory of human evolution seem to change more frequently than theories in other branches of science. The article concludes with this observation:

“I always tell my students that I've taught for 30 years and I've never given the same lecture twice. Hardly a year goes by when something new isn't found,” says Dr. Leslie Aiello, a paleoanthropologist at University College London. Of the Floresian discovery she says, “It's a total knockout.”


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