A discovery in a cave on the Indonesian island of Flores, reported 10 years ago, moved one scientist to hail it as “the most important find in human evolution for 100 years.” The fragmentary bones, but only one full skull, of several individuals led the discoverers to conclude that these were remains of a previously unknown extinct species of humans.
The Australian and Indonesian scientists named the species Homo floresiensis. Some took to calling these unusually little people, who had apparently lived on the island as recently as 15,000 years ago, the hobbits. It was mystifying that people with brains apparently no larger than a chimpanzee’s, one-third that of modern Homo sapiens, would have been capable of making the stone tools found in the cave around them.
From almost the beginning, a few skeptics raised warning flags. Was the one skull sufficient evidence of a distinct human species? These people were small, yes, but how could the Flores skull be proved normal and not that of a modern human with any of a number of growth disorders that shrink the head and brain?
The skeptics have now revived the debate with two papers published on Monday in The Proceedings of the National Academy of Sciences. One article points out what are said to be flaws in the original research reports. The second one describes evidence suggesting the individual was born with Down syndrome.
Among the flaws, the critics say, were underestimates of the stature and the brain size of the most complete skeleton, designated as LB1, from Liang Bua Cave. In their view, LB1’s stature was a little more than four feet tall, not 3.5 feet as in the original estimate. New measurements of the possible brain size were likewise large.
The authors of the first journal paper — Robert B. Eckhardt and Alex S. Weller of Penn State University, Maciej Henneberg of the University of Adelaide, in Australia, and Kenneth J. Hsu of the National Institute of Earth Sciences in Beijing — concluded that the defining features of the specimen as originally described “do not establish the uniqueness or normality necessary to meet the formal criteria for a type specimen of a new species.”
The lead author of the second paper on the Down syndrome hypothesis was Dr. Henneberg, a professor of anatomy and pathology, with Dr. Eckhardt, a professor of developmental genetics and evolution, as a co-author.
Based on a re-examination of the available evidence, the researchers said the revised dimensions of the LB1 cranium and femur fell in the range predicted for an individual with Down syndrome from that region of Indonesia. The larger size estimate also matches that of some people today on Flores and other Pacific islands.
The scientists also pointed to the skull’s asymmetry, a left-right mismatch of facial features, as characteristic of people with Down syndrome, one of the most common developmental disorders in humans. They noted that it occurred in more than one human birth per 1,000.
Other scientists who tended to accept the new-species interpretation have so far rejected what they call the “sick hobbit hypothesis.” Dean Falk, an anthropologist at Florida State University who specializes in brain evolution, used CT scans of the Flores cranium that she said showed no sign of growth disorders.
Last year, Karen L. Baab of Stony Brook University and colleagues reported on a comprehensive study of the cranium, showing that it was “clearly distinct” from skulls of healthy modern humans.” They said the findings “counter the hypothesis of pathological conditions.”
So far, searches in other caves on Flores and elsewhere have failed to yield the additional bones, especially more skulls, needed to determine if LB1 is one of a kind or one of an extinct human species, Homo floresiensis. Until then, Dr. Eckhardt said, the new analysis yielded a “less strained explanation” than adding another branch to the human family tree. The signs, he said, “point rather clearly to Down syndrome.”
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