Hallucial convergence in early hominids.

There is a richly documented fossil record of the evolutionary transition from ape-sized brains that are less that one-third the size of modern humans through a series of intermediate-sized brains up to the modern range. The first report on the discovery of the foot of the Stw 573 skeleton emphasized the apparent transitional nature of its great toe [Clarke, R.J., Tobias, P.V., 1995. Sterkfontein Member 2 foot bones of the oldest South African hominid. Science 269, pp. 521-524]. The hallux appeared to be intermediate in its divergence between human-like adduction and ape-like abduction. A major part of this evidence is the medial encroachment of the metatarsal I facet on the medial cuneiform. This study quantifies the variability of this feature in extant hominoids and fossil hominids. The results are consistent with the view that all currently known hominids were specialized for bipedality and lacked the ape-like ability to oppose the great toe.