ABSTRACT
The evidence presented deals not with the early states of human evolution, but with the unequivocal occurrence of H. erectus from the Koobi Fora Formation, east of Lake Turkana. This chapter presents decisive evidence that shows the existence of two contemporaneous hominid species in the Koobi Fora area. The cranium consists of a complete calvaria and a great deal of the facial skeleton, including the nasal and zygomatic bones. The contemporaneity of Homo erectus and a robust Australopithecus is now clearly established over the period during which the Upper Member of the Koobi Fora Formation was deposited. The single species hypothesis has served a useful purpose in focusing attention on variability among the early hominids and also on the ecological consequences of hominid adaptations. Among the variety of hypotheses put forward to accommodate the evidence in an evolutionary framework, the most explicit and directly simple is the single species hypothesis.
