Scientists wage ongoing debate over tiny hominid's origins in Science
By Tabitha M. Powledge | May 19, 2006
Scientists have moved their debate over the origins of the Hobbit onto the pages of this week'sScience. In the journal, two groups of authors argue whether or not the Hobbit -- the 18,000 year-old bizarre-looking tiny hominid unearthed on the Indonesian island of Flores in 2003 -- is a new human species or just a member of Homo sapiens with microcephaly, a heterogeneous head and brain deformity.
"I don't expect this to settle the argument, but I'm relieved that we got something published in a peer-reviewed journal," Robert Martin, primatologist at Chicago's Field Museum, told The Scientist.
In the journal, Martin and his colleagues critique a 2005 Sciencepaper that analyzed an endocast of the skull from the Hobbit type specimen, LB1, and compared it to a single microcephalic skull. Based on the results, the 2005 paper concluded that LB1 was not microcephalic. Martin and his team, however, argue that LB1's skull shares characteristics with other microcephalic skulls collected from humans, suggesting that microcephaly is still a strong possibility.
The authors of the 2005 paper, led by Dean Falk, endocast expert at Florida State University in Tallahassee, respond in the journal that Martin and his colleagues do not provide comparative measurements and photos of their microcephalic skulls, making conclusions impossible.
Falk told The Scientist that Martin and his colleagues' criticisms are historically familiar. "When important fossils are discovered, there's always a brouhaha, always people who say they're pathological," she said.
Both papers predict hominid brain sizes by comparing hominids to other mammals, but that can produce misleading results, said paleoanatomist William L. Jungers, State University of New York at Stony Brook. "There's no law of mammalian brain scaling. Based on our size, you would never predict that humans have the brains that we have," said Jungers, who was not on the discovery team but is analyzing Hobbit postcranial remains. "We don't have good models for predicting brain-size evolution in any human lineage."
Experts not involved with either group say it may never be clear whether LB1 was microcephalic because the condition is so diverse. LB1's teeth are too large and bones too thick to be an example of microcephalic osteodysplastic primordial dwarfism (MOPD) type 2, the only specific suggestion in the Martin group's paper, according to medical geneticist Judith Hall, Vancouver BC Children's Hospital, who has studied that disorder. But microcephaly of some previously unknown kind is perfectly plausible in an inbred group, she told The Scientist.
Ralph Holloway, of Columbia University, who has studied endocasts of LB1 and microcephalics, said that LB1's brain has several peculiar features, but they don't resemble microcephalics he's examined. "It's possible that pathology exists," he said. But last year the discovery team reported finding a second small mandible very like LB1's, which is "is a very serious nail in the coffin of pathology," he added. "I waffle on this."
"I'm not decided about what I think," John Hawks, anthropologist at the University of Wisconsin, told The Scientist. Hawks agrees that the second jaw is the strongest evidence for LB1 being a representative Hobbit, but he believes LB1's skeleton displays odd features that may be pathological.
As it happens, discussions in scientific venues are moving from Hobbit skulls to Hobbit skeletons, but it's unclear whether this new evidence will clarify classification. Jungers and Stony Brook colleague Susan Larson have analyzed postcranial material at recent paleoanthropology meetings and have a paper out for review. They have found limb proportion convergences between the Hobbit and Lucy, the famous type specimen of Australopithecus afarensis, but shoulder characteristics more closely match early Homo erectus, he noted. The discovery team originally hypothesized that the Hobbits were H. erectus descendants, but have largely abandoned that idea.
Links within this article
T. Powledge, "Return of the Hobbit," The Scientist, October 13, 2005.
D. Falk et al, "The brain of LB1, Homo floresiensis," Science, April 8, 2005.
T. Powledge, "No microcephaly for Hobbit," The Scientist, March 4, 2005.
MJ Morwood et al, "Archaeology and age of a new hominin from Flores in eastern Indonesia," Nature, October 28, 2004.