Homo Floresiensis - Bone Structure

Bone Structure

The bone structure of H. floresiensis’ shoulders, arms and wrists has been described as very different from modern humans', much closer to the bone structure of chimpanzees or an early hominin. This adds support to the idea that H. floresiensis is a separate species of early human rather than a modern human with a physical disorder.

Susan G. Larson et al. analyzed the upper limb of LB1. They found that in LB1 the angle of humeral torsion is much less than in modern humans. This had been previously studied by Richards et al., who declared that it is a sign of modern pygmy populations, and T. Jacob et al., who pointed out that muscle attachments on the bone suggest LB1 had weak muscles which resulted in little development of humeral torsion. Larson et al. rejected Richards’ conclusion, arguing that the humeral torsion of pygmy populations is usually similar to that of peoples of average stature. They argued that Richards et al. cited a 1972 paper which had studied a sample of six female Eastern Central African pygmies and this sample was too small to represent the whole population. Larson et al. also failed to find signs of microcephaly on the studied bones.

Larson et al. also studied the relatively short clavicle and the unusual formation of the pectoral girdle. They compared their finding with the skeleton of Nariokotome Boy (variously classified as H. ergaster or H. erectus), and suggested that the pectoral girdle of H. floresiensis was a transitional stage in human shoulder evolution.

While some specialists, including paleoanthropologist Russell Ciochon of the University of Iowa, supported the conclusion, others, including Eric Delson of Lehman College, City University of New York, pointed out that the recent sample of H. floresiensis individuals is too small and that Larson's research was based just on one shoulder bone.

Tocheri et al. (2007) (including Morwood, Larson, and Jungers), compared three carpal bones believed to belong to LB1 with carpal bones of modern humans, some earlier hominids and African apes. They concluded that the carpals from the Liang Bua cave resembled ape carpal bones and were significantly different from the bones of H. sapiens, Homo neanderthalensis or even Homo antecessor, and that they were comparable to carpal bones of Australopithecus. The carpal bones of H. floresiensis were found to lack features that evolved with ancestors of modern humans at least about 800,000 years ago. These features are already formed during embryogenesis and therefore Tocheri et al. argue that it is improbable that the shape of H. floresiensis wrist bones could be a result of a developmental disease. This evidence also suggests that H. Florensiensis is not a modern human with an undiagnosed pathology or growth defect, but that it represents a species descended from a hominin ancestor that branched off before the origin of the clade that includes modern humans, Neandertals, and their last common ancestor.

This conclusion was challenged by Robert Martin, since Jacob's death the leading proponent of the microcephaly hypothesis, and Alan Thorne. Martin noted that no research has been done on wrists of microcephalic people. Thorne maintained that the differences were small and that similar variation could occur with living modern humans. He also pointed out that the carpal bones had been found scattered in the cave and it was not certain that they all belonged to the same individual. Project leader Morwood countered that there were also other features, such as the stature, body proportions, brain size, shoulder, pelvis, jaw, and teeth which suggested that H. floresiensis is a separate species that evolved in isolation on the island.