Bilateral asymmetry of the humerus in Neandertals, Australian aborigines and medieval humans

Abstract

High levels of directional asymmetry of cross-sectional shape and properties in medieval farmers may be caused by the performance of more physically demanding tasks using one side of the body from an early age in that population. Various patterns of asymmetry in Neandertals and modern humans may be caused by different habitual behaviors during growth, eco-geographic patterns in body proportions, genetic factors, and differences in ontogeny.

Variation and Correlations in Departures from Symmetry of Brain Torque, Humeral Morphology and Handedness in an Archaeological Sample of Homo sapiens

“…Moreover, scaling to bone length provides greater compatibility between the results obtained in this study, and those found in the literature [1,42,52,56]. Ratios of principal moments of area (Imax/Imin) and relative cortical area (%CA) were not standardized either to humeral length or to body mass [42,57]. The anatomical traits quantified on the endocast and the humeri are of different natures.…”

“…Moreover, this biomechanical property is very variable within human populations and can express phylogenetic information [68], which is why interpretations of DA Imax/Imin on a small sample size should be drawn with caution. Previous research on the same sample showed that this medieval population was characterized by significant and more pronounced DA of all biomechanical properties (%CA, J and Imax/Imin) than Neandertals and recent Aboriginal Australians [42]. The discrepancy between these results is probably a consequence of analyzing leftand right-handed individuals separately in the last research.…”

“…In this context, although some anatomical and structural components of the brain are related to hand preference, they have not yet been precisely delimited and the relationships with details of the surface of the brain endocast remains to be established [2]. The same conclusion can be drawn for the interpretation of hand preference, as deduced from post-cranial elements [42]. The main limitation is, of course, the application of this knowledge, resulting from separate studies (focused respectively on the brain/endocast, on biological skeletal adaptations to lateralized behaviors, and on hand preference) to specimens of past human societies, including fossils from other species than Homo sapiens.…”

“…Previous studies have focused on gross external anatomy (see review [40]) or on analyses of single CT slices [1]. A recent in vivo study shows the limitations of earlier methodologies [41] and suggests that 'hand preference' can be successfully inferred from measures of upper limb geometric asymmetry [42]. Relationships between cortical and trabecular architecture and functional patterns are also more complex than previously thought and need further investigation [41,43].…”

A case of marked bilateral asymmetry in the sacral alae of the Neandertal specimen Regourdou 1 (Périgord, France)

“…Therefore, the sacrum does not have a long period in which it may be sensitive to lateralized habitual behavior or loading. However, Neandertals and Late Pleistocene humans exhibited stronger asymmetry in the upper limbs than do the majority of extant humans (Sparacello, Villotte, Shackelford, & Trinkaus, ; Trinkaus, Churchill, & Ruff, , but see Kubicka, Nowaczewska, Balzeau, & Piontek, ). There is no evidence of similarly strong compensatory asymmetry in the lower body (Ruff, Trinkaus, Walker, & Larsen, ; Trinkaus et al, ), which given the small number of Neandertal sacra preserved, prevents any assumptions about sacral asymmetry in Neandertals.…”