This research was conducted in 1991-1996 in collaboration with the PalaeoAnthropology Research Unit, Department of Anatomical Sciences, University of the Witwatersrand Medical School. I thank Professor P.V.Tobias (Director) for his kind permission to study the archaeology, Dr R.J.Clarke (director of the Sterkfontein excavation) for his collaboration, the Palaeo-Anthropology Scientific Trust, which has financed the overall Sterkfontein project, and the Foundation for Research Development for their financial support. I especially thank the L.S.B.Leakey Foundation and the Boise Fund of the University of Oxford for grants in archaeology. All figures have been drawn by Wendy Voorvelt, who has provided extensive technical assistance in many aspects of this research. Finally, I thank Drs R.J.Clarke, A.Keyser and the referees for reading the manuscript and offering valuable advice, and Drs F.Thackeray, L.Berger and K.Kuykendall for helpful discussions about their sites.