Skeletal remains found in 2004 in a cave on the island of Flores in Indonesia were not proof of a new species of "hobbit" human, but instead showed signs of Down syndrome, argues a new study.
The initial analysis of the skull (called LB1) suggested a brain that was 1/3 the size of the average modern humans, and a small stature -- just about 3 1/2 feet tall. The skull was dated to 15,000 years ago, and considered a distinct species -- Homo floresiensis. (See a 3-D image of the skull).
But a reanalysis by an intentional team found that initial estimates were "markedly lower than any later attempts to confirm them," the study's authors said.
"The difference is significant, and the revised figure falls in the range predicted for a modern human with Down syndrome from the same geographic region," Robert B. Eckhardt, professor of developmental genetics and evolution at Penn State, said in a statement.
"The skeletal sample from Liang Bua cave contains fragmentary remains of several individuals," Eckhardt said. "LB1 has the only skull and thigh bones in the entire sample."
Eckhard, along with his colleagues -- Maciej Henneberg, professor of anatomy and pathology at the University of Adelaide, and Kenneth Hsü, a Chinese geologist and paleoclimatologist -- say the skull is from an abnormally developed human.
The skeleton's initial size was estimated based on a short thigh bone combined with a formula used with an African pygmy population, the authors say. But humans with Down syndrome also have short thigh bones, Eckhardt said.
"When we first saw these bones, several of us immediately spotted a developmental disturbance," Eckhardt said, "but we did not assign a specific diagnosis because the bones were so fragmentary. Over the years, several lines of evidence have converged on Down syndrome."
The skull is asymmetrical, for example, which is to be expected from a human with Down syndrome, along with other characteristics that only appeared in the "hobbit" skeleton, but not in the other fossils found in the same cave, Eckhardt said.
"Are the skeletons from Liang Bua cave sufficiently unusual to require invention of a new human species?" Eckhardt said. "Our reanalysis shows that they are not. Here the signs point rather clearly to Down syndrome, which occurs in more than one per thousand human births around the world."