Sexual Dimorphism in the Mandible of Homo Neanderthalensis and Homo Sapiens: Morphological Patterns and Behavioural Implications

Introduction In 1980 the Journal of Human Evolution devoted an issue to papers which examined sexual dimorphism in hominid evolution. Two of the contributing authors, Smith and Trinkaus, independently investigated intersexual differences in skeletal patterning in the middle to late Pleistocene species Homo neanderthalensis. They also sought to link the patterns they identified to aspects of its behaviour. Surprisingly, they arrived at different conclusions on both counts. Smith (1980) argued his craniometric analyses indicated that the Neanderthals were slightly more dimorphic than anatomically modem humans. From this he inferred that the Neaoderthals had a more pronounced sexual division of labour than is common among more recent human groups. In contrast, Trinkaus (1980) suggested his post-cranial analyses indicated that the level of sexual dimorphism exhibited by H. neanderthalensis was indistinguishable from that seen in Homo sapiens. From this he inferred that the Neanderthals were probably about as polygynous as the majority of ethnographically-known societies. Since 1980 these conflicting claims have beeo largely ignored. This is despite the potential contribution an understanding of sexual dimorphism and its associated behavioural inferences could make to our knowledge of Neanderthal bio-cultural evolntion (Wood 1985). In this paper we reconsider both areas of disagreement between Trinkaus (1980) and Smith (1980) over sexual dimorphism in H. neanderthalensis. We begin by reporting the results of an analysis of a sample of H. neanderthalensis and H. sapiens mandibles. This was designed to determine whether the picture of sexual dimorphism presented by mandibular remains was consistent with the findings of the other studies. We then report the results of an analysis of sexual dimorphism in a sample of primate mandibles. This aimed to establish whether the results derived from the fossil mandibular remains were biologically meaningful. Finally we outline a model of sexual differences in behaviour in Upper Pleistocene hominids based on biomechanical principles.