Origin of Bipedal Locomotion

Abstract

Bipedalism is a highly specialized and unusual form of primate locomotion that is found today only in modern humans. The majority of extinct taxa within the Hominini were bipedal, but the degree to which they were bipedal remains the subject of considerable debate. The significant discoveries of fossil hominin that remains in the last 40 years have resulted in this debate becoming increasingly focused on how bipedal certain fossil taxa were, rather than on the overall process. Although the early hominin fossil record remains poor, evidence points to at least two distinct adaptive shifts. First, there was a shift to habitual bipedalism, as typified by certain members of Australopithecus, but possibly including earlier genera such as Ardipithecus and Orrorin. Such taxa were bipedal, but also retained a number of significant adaptations to arboreal climbing. The second shift was to fully obligate bipedalism and coincides with the emergence of the genus Homo. By the Early Pleistocene, certain members of Homo had acquired a postcranial skeleton indicating fully humanlike striding bipedalism. The final part of this chapter reviews why bipedalism was selected for. There have been many theoretical explanations, and the most robust remain those linked to the emergence of more varied habitats. Such an environmental shift would have involved strong selection for new behavioral strategies most likely linked to the efficient procurement of food.