Mechanisms of hominoid dispersal in Miocene East Africa

The thesis of this essay is that the ecological changes which occurred during the Miocene in East Africa, created both the need and the conditions for the development of dispersal behaviour and other adaptations. The major ecological change in East Africa during the Miocene was the break-up of the relatively homogenous, lowland, tropical rainforest. The forest break-up was due to the combined effects of climatic change and rifting. The result of the fragmentation for species adapted to the forest, was increasing resource limitation. Species responded either by retreating with the forests, becoming extinct, or by evolving or developing new behaviours to cope with the new environment. The focus of this paper is upon the development of dispersal as a behaviour pattern for locating patchy resources. An ecological model is advanced to explain the development of dispersal and to place it in the context of other competing evolutionary responses to the ecological changes of the Miocene. The anatomical evolution of the Old World monkeys and apes during the Miocene is looked at in terms of the model. Bovid evolution over the same period is also looked at as evidence of a broad, episodic turnover in response to the ecological changes. It is suggested that hominid bipedalism may also fit the model and may have evolved as an adaptation for dispersion.