ABSTRACT
This article is an attempt to reopen the problem of origins by examining critically some of the existing models of hominid differentiation, and to suggest a new one based on a fresh approach. Perhaps recognising this, adherents of the "predatory chimpanzee" model tend to situate the hominidpongid divergence in the late Pliocene, and regard all known fossils of basal Pleistocene Hominidae as representative of a short-lived transitional phase of imperfect hunting adaptation. While none of the previous models of hominid differentiation is without plausibility, none is very convincing. While there is little evidence for catastrophic desiccation in the tropics of the kind demanded by some models of hominid differentiation, there are indications that a trend towards seasonality persisted through the Tertiary, especially in Africa. A medium-sized Dryopithecus of the Miocene is a reasonable starting-point for hominid differentiation, and increased seasonality in the Middle-to-Upper Miocene and Lower Pliocene makes it likely that Phase I differentiation began at that time.
