Anatomical comparisons of human, chimpanzee, H. erectus and A. afarensis. a, c, Anterior and posterior views of human, enumerating features related to endurance running listed in previous table. b, d, Anterior and posterior views of chimpanzee. Labelled muscles connect the head and neck to the pectoral girdle and are reduced or absent in humans. e, Reconstruction of H. erectus based primarily on KNM-WT 15000; f, reconstruction of A. afarensis based primarily on AL-288.
Bramble DM, Lieberman DE (2004) Endurance running and the evolution of Homo. Nature 432:345-352.