L’architecture de l’épaule au sein du genre Homo : nouvelles interprétations

The morphology of human clavicles can be estimated by projecting them on two perpendicular planes in order to assess the shapes of their cranial and dorsal primary curvatures. In cranial view no differences in curvature appear within the genus Homo, which means the different species had similar arms elevation capacity, especially in protraction. On the contrary, in dorsal view two clavicles morphologies could be defined. The first one is characterized by two curvatures in dorsal view and is possessed by all Homo species, from Homo habilis to Neanderthal, including Homo ergaster, but not modern human, Upper Paleolithic and anatomically modern human remains, who possess clavicles of the second type, characterized by either one curvature, or two slightly pronounced ones in dorsal view. Clavicles displaying two pronounced curvatures in dorsal view are associated with scapula sitting high on the thorax in regard to modern human. However, shoulder with high scapula on the thorax displays two different kinds of architectures: (i) shoulder with short clavicles associated to scapulas sitting more laterally than those of modern human. This group includes earlier Homo like Homo habilis and Homo ergaster and (ii) shoulder with long clavicles associated to scapulas sitting more dorsally on the thorax, like those of modern human. This group includes Homoantecessor and Neanderthals. In other words, within the genus Homo, three shoulders would have existed. Evolution of the shoulder complex is far more complex than previously thought and the arrival of modern bipedalism was not associated to modern shoulder.