The Origins of Bipedal Locomotion William E. H. Harcourt-Smith* Department of Anthropology, Lehman College CUNY, Bronx, NY, USA Department of Anthropology, The Graduate Center CUNY, New York, NY, USA Department of Vertebrate Paleontology, American Museum of Natural History, New York, NY, USA 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 behav- ioral strategies most likely linked to the efficient procurement of food. Introduction Bipedal locomotion sets modern humans apart from all other living primates. We are the only obligate bipeds among well over 200 extant primate species. It therefore stands to reason that this unusual and highly derived form of locomotion has attracted much attention from those who study human evolution. Current evidence points to anatomical traits strongly associated with bipedalism relatively deep in the hominin lineage (Ward et al. 2001) and well before the advent of other “traditional” human traits such as larger brains and tool use. This chapter reviews the current state of thinking on this unique form of primate locomotion. In order to understand the origins of hominin bipedalism, one first has to understand the mechanisms that make it such an efficient form of locomotion in modern humans. In the first section of this chapter, I will briefly explore the nature of the modern human walking cycle and the associated anatomical traits that facilitate it. I will then explore the fossil evidence for the origins of bipedalism and speculate on the likely locomotor behaviors that preceded it. Finally I will discuss some of the theories surrounding why bipedal locomotion was selected for. *Email: willhs@amnh.org Handbook of Paleoanthropology DOI 10.1007/978-3-642-27800-6_48-3 # Springer-Verlag Berlin Heidelberg 2013 Page 1 of 36