Structural effects of variation in the human clavicle

International audienceObjectives: Purported evolutionary shifts in shoulder structure have been linked to changes inhominin behavior and adaptation. Researchers use clavicle morphology to infer these shifts.However, there is a lack of empirical data underlying such predictive relationships. This studyinvestigates how clavicle morphology affects articulated shoulder girdle and upper thorax configurationin humans.Materials and Methods: Landmarks and scalar measurements on the clavicle, scapula, and ribs1–3 were collected from three-dimensional computed tomographic scans of living humans.Covariation between disarticulated and articulated morphology was assessed using partial leastsquares and regression analyses.Results: We found support for hypotheses linking combined dimensions of the clavicle, ribs, andscapula to resting protraction. Individuals with relatively short clavicles tend to exhibit protractedand elevated resting positions of the scapula. It is more difficult to predict superoinferiorconfiguration, which is only minimally affected by clavicle curvature. Instead, the superoinferiorposition of the scapula on the thorax is governed equally by clavicle orientation and rib declination.Shoulder breadth is determined primarily by clavicle length, but orientation has a comparableeffect. Therefore, reliable reconstructions of shoulder breadth can be established usingclavicle length, together with consideration of orientation. Relationships between clavicle andthorax morphology are weaker.Discussion: Understanding the determinants of variation in human shoulder structure informsinterpretation of skeletal remains. Our investigations describe how important aspects of shoulderstructure can be inferred from disarticulated clavicles and we provide the attendant predictiveequations. Future work on interspecific variation will improve skeletal reconstruction formore ancient hominins