A study led by Dr Katerina Harvati from Tübingen University, Germany, suggests the small-brained Indonesian hominin was a distinct species of human, rather than Homo sapiens suffering from a developmental disorder.

A joint Australian-Indonesian team of archaeologists unearthed partial skeletons of nine small-bodied hominins on the Indonesian island of Flores in 2003. Among the specimens found were an 18,000-year-old almost complete skull (labeled LB1) and a partial skeleton, consisting of leg bones, parts of the pelvis, hands and feet, and some other fragments. The fossils have been attributed to a new human species, Homo floresiensis.

LB1 was an adult of about 30, probably female. She was only about 3.3 feet (1 m) in height with a very small brain size of 417 cc.

Since the discovery, researchers have clashed over whether LB1 really does represent a species of its own, a descendant of Homo erectus or a pathological form of Homo sapiens.

“The origin of hominins found on the remote Indonesian island of Flores remains highly contentious,” Dr Harvati and her colleagues wrote in a paper reporting the findings in the open-access journal PLoS ONE.

“These specimens may represent a new hominin species, Homo floresiensis, descended from a local population of Homo erectus or from an earlier migration of a small-bodied and small-brained hominin out of Africa. Alternatively, some workers suggest that some or all of the specimens recovered from Liang Bua are pathological members of a small-bodied modern human population. Pathological conditions proposed to explain their documented anatomical features include microcephaly, cretinism and Laron syndrome.”

Dr Harvati’s team compared the LB1 skull to skulls of healthy modern humans, humans with microcephaly and other pathological conditions, archaic Homo using methods of 3D geometric morphometrics. The methods use 3D coordinates of cranial surface anatomical landmarks, computer imaging and multivariate statistical analysis to achieve a detailed analysis of shape.

“This is the most comprehensive study to date to simultaneously evaluate the two competing hypotheses about the status of Homo floresiensis.”

The scientists found that the LB1 skull shows greater affinities to the fossil Homo sample than to pathological modern humans. Although some superficial similarities were found between LB1 and skulls of modern humans with pathologies, additional features linked LB1 exclusively with fossil Homo.

Analyses of data show that LB1 is “clearly distinct from healthy modern humans and from those exhibiting hypothyroidism and Laron syndrome. Modern human microcephalic specimens converge, to some extent, on crania of extinct species of Homo. However in the features that distinguish these two groups, LB1 consistently groups with fossil hominins and is most similar to H. erectus,” the authors wrote.

“Our study provides further support for recognizing the Flores hominins as a distinct species, H. floresiensis, whose affinities lie with archaic Homo.”

Dr Harvati and colleagues said: “our findings provide the most comprehensive evidence to date linking the Homo floresiensis skull with extinct fossil human species rather than with pathological modern humans. Our study therefore refutes the hypothesis that this specimen represents a modern human with a pathological condition, such as microcephaly.”

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Bibliographic information: Baab KL, McNulty KP, Harvati K. 2013. Homo floresiensis Contextualized: A Geometric Morphometric Comparative Analysis of Fossil and Pathological Human Samples. PLoS ONE 8 (7): e69119; doi: 10.1371/journal.pone.0069119