The ischium and hip extensor mechanism in human evolution.

Although it is commonly stated that the ischia of the late Pliocence-early Pleistocene hominid fossils are long and ape-like, new interpretations show this view to be falacious. An important new theory proposed by Robinson concludes that the gracile form of early hominid was an efficient biped, but the robust form was a less efficient biped and was adapted for tree climbing. Interpretation of the ischium is crucial to this idea. The present study shows that (1) the gracile and robust australopithecine ischia had similar relative lenths and (2) that the hamstring mechanism was probably very similar in the two forms of South African early hominid.