DOUBLE TROUBLE? A second small Hobbit skull similar to the first [right] would convince some skeptics—but not all of them—that they are dealing with a new species, as opposed to a dwarf or a diseased human [left].
COURTESY OF KIRK E. SMITH/Electronic Radiology Laboratory, Mallinckrodt Institute of Radiology

For three years researchers have feuded over the rightful classification of the Hobbit, a diminutive, 18,000-year-old specimen unearthed from the Indonesian island of Flores. Is it an entirely new species, as its discoverers have maintained, or merely a small-brained human? Last week, officials reopened the site where the Hobbit was found as well as a newly discovered cavern underneath it, raising hope that diggers might soon bring convincing new evidence to bear.

A second skull would be especially helpful. Critics of the new species theory have latched onto the Hobbit's measly 400-cubic-centimeter brain as a sure sign of an abnormality called microcephaly in which the brain does not reach normal size. Some prominent advocates of a human Hobbit say that a second skull could settle the debate. "It's the acid test," says primatologist Robert Martin of the Field Museum in Chicago, who contends that the existing Hobbit skull is a malformed human skull. If he is correct, a second skull would be closer to 1,000 cubic centimeters, he says.

A newfound skull just as small, however, would weaken the microcephaly view, agrees John Hawks, a paleoanthropologist at the University of Wisconsin–Madison. "I completely accept that the skeleton is pathological," he says. Nevertheless, "if a second skull were found with the same brain size as the first, the game is over. We find humans with extremely small brain size once in a while, but finding two in an archaeological sample is just implausible, unless they sample a population where extremely small brains are the norm."

Some other holdouts against the separate species view say the question is less straightforward. "Reopening the cave is great and I am confident that the investigators will find more material similar to that already recovered," says evolutionary biologist Gary Richards of the University of California, Berkeley, who has argued that the Hobbit represents a dwarfed—but healthy—human. "Unlike others, I am of the opinion that this will not confirm that the remains are a [new] species."

According to Richards, if the Hobbit specimen is truly a dwarf, it would not have been the only one. Thanks to inbreeding, "significant numbers of individuals would have been present in the population that shared the same condition, so multiple individuals are to be expected," he says. Evolutionary biologist Robert Eckhardt of Pennsylvania State University, a proponent of the pathological view, says he would take another pea-brained Hobbit as sign of a hereditary deformity, given the existence of human families in which microcephaly was passed down through several generations.

So what would it take to convince hardcore skeptics that the Hobbit is its own species? Eckhardt says the question "approaches this problem from the wrong way around," because in his view the specimen's pathology is well established.

Richards says the question of the Hobbit's species status is currently unanswerable. The intriguing part, he notes, is what the Hobbit can teach us about evolution. As he sees it, the genetic pathways that lead to dwarfism in modern humans are well understood, and a detailed study of multiple Hobbit specimens could help tease apart which pathways gave rise to and maintained this lilliputian population.

"The import of this to understanding the history of evolutionary change in the human lineage is huge," he says. "But most of my colleagues would rather argue about whether or not this represents a new species." That debate could ultimately be resolved but "only by keeping an open mind about these remains are we going to be in a position to determine whether they represent a new species," he says.