'Hobbit' Human May Not be a New Species: Down Syndrome to Blame for Unusual Features

The so-called "hobbit human" has captured the imaginations of the public across the globe. Excavation of fragmentary skeletal remains from the island of Flores revealed what seemed to be a previously unknown species of human, dubbed Homo floresiensis. Now, though, researchers have found that the single specimen may not be a new species, but instead may be a developmentally abnormal human.

The skeleton, which is dubbed LB1, has unusual anatomical characteristics. It has a skull with a cranial volume of only 23.2 cubic inches, suggesting a brain less than one third the size than a modern human's, in addition to short thighbones, which made the person stand about 3.5 feet tall. While LB1 only lived 15,000 years ago, comparisons were made to earlier hominins.

Yet a closer examination reveals that this "new" species may not be so new. The researchers pointed out that the original figures for cranial volume and stature are underestimates. This could mean that the remains are actually of that of a developmentally abnormal modern human.

"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," said Robert Eckhardt, one of the researchers, in a news release. "When we first saw these bones, several of us immediately spotted a development disturbance, 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."

So what indicators are there? The first is craniofacial asymmetry. The left-right mismatch seen on the specimen is characteristic of Down syndrome. In addition, short thighbones are also a characteristic.

 "This work is not presented in the form of a fanciful story, but to test a hypothesis: Are the skeletons from Liang Bua cave sufficiently unusual to require invention of a new human species?" asked Eckhardt in a news release. "Our reanalysis shows that they are not. The less strained explanation is a developmental disorder. Here the signs point rather clearly to Down syndrome, which occurs in more than one per thousand human births around the world."

The findings are published in the journal Proceedings of the National Academy of Sciences.