Palaeoclimates, plasticity, and the early dispersal of Homo sapiens

The origin and initial dispersal of Homo sapiens out of East Africa and into the Levant remains a major research focus in evolutionary anthropology. There is little doubt that climatic changes played a role in facilitating this dispersal, but the specific dynamics remain poorly understood. This contribution surveys the fossil and genetic evidence for the origin and dispersal of modern humans, and situates this evidence within the context of biological theories of plasticity and dispersal. It is shown that certain climatic and environmental conditions are expected to lead to the evolution of plastic strategies, and that such strategies are characteristic of successfully dispersing species. A model is formulated that allows for the identification of features in climatic records that are conducive to the evolution of plasticity, and thus to the development of dispersal capabilities. Using as an example a palaeoclimatic record from Lake Tana, Ethiopia, the model is used to pinpoint the chronology of likely periods of dispersal from East Africa. Results indicate the presence of a dispersal phase c.97–105 ka, a date that fits well with the initial modern human colonisation of the Levant shortly after 100 ka. Implications of recent genetic chronologies for the origin of non-African modern humans and the archaeological evidence for possible routes out of Africa are discussed in this context.