Who knew that I'd have occasion to write about the hobbits again, so soon after my last post on the subject?
A paper published yesterday in PLoS ONE is fanning the flames of controversy over the wee human remains from Flores, Indonesia. In it paleoanthropologist Lee Berger of the University of the Witwatersrand in Johannesburg, South Africa, and his colleagues report on small human bones from two caves in Palau, Micronesia. The bones date to between 1,400 and 2,900 years ago. See this story from National Geographic (which helped fund the research) for an account of the discovery.
According to the authors, bones from the older levels of the caves are quite small, even when compared to pygmy populations from Southeast Asia. They may therefore be an example of island dwarfing, a known biological phenomenon in which mammals larger than rabbits evolve smaller proportions as an adaptive response to the paucity of resources available on small islands. Furthermore, these early Palauans exhibit a number of traits that are typically associated with earlier members of our genus, including large teeth, a small face and a non-projecting chin. These characteristics also occur in the hobbits from Flores, and have been used to help make the case that the hobbits represent a previously unknown species of human, Homo floresiensis. But Berger and his colleagues contend that these features may simply arise as a side effect of getting small. And that, they say, "would be consistent with the argument that Flores LB1 [the most complete of the Flores individuals] may represent a congenitally abnormal individual drawn from a small-bodied population of H. sapiens."
The Palau bones certainly underscore just how variable modern humans are. But do they really spell trouble for the theory that the Flores hobbits represent a new human species? I don't think so. Although Berger estimates that the Palau people had a brain size close to the low end of the modern human range, that's still a lot bigger than LB1's brain, which was on par with a chimp's. And hobbit critics have yet to come up with a genetic disorder that can account for LB1's diminutive brain size and all of her other odd traits. Furthermore, some aspects of LB1's skeleton are simply not found in H. sapiens. Her wrist bones, for example, look just like a chimpanzee wrist and nothing like our own. This is particularly strong evidence for LB1 belonging to a different species, because the wrist takes shape in the first trimester of pregnancy, well before most growth disorders could affect it. According to the National Geographic report, Berger's team has yet to study the wrist bones of the Palau folks.
One last tidbit: according to a story on ScienceNOW, other excavations on Palau have turned up individuals of normal body size that are the same age as the tiny people Berger found. To quote from the story:
"...archaeologist Scott Fitzpatrick of North Carolina State University in Raleigh, who has worked in Palau for a decade, says he doesn't think the bone beds represent a true population. In a site only 4 kilometers from Berger's caves, he has excavated the burials of Palauans of similar age--and normal stature. That would seem to rule out isolation and island dwarfing, he says. 'It would be very unusual to have a group of people living in close contact with a normal size population who evolved to be smaller.' Instead, 'the most parsimonious explanation is that they were Palauans with a genetic anomaly leading to small people who were buried in a clan or family plot.'"
Edited by katewong at 03/12/2008 12:38 PM