Jacobs, Zenobia; Roberts, Richard G.; Galbraith, Rex F.; Deacon, Hilary J.; Grun, Rainer; Mackay, Alex; Mitchell, Peter; Vogelsang, Ralf; and Wadley, Lyn, 2008, Ages for the middle stone age of Southern Africa: implications for human behavior and dispersal, Science, 322, 733-735.
The expansion of modern human populations in Africa 80,000 to 60,000 years ago and their initial exodus out of Africa have been tentatively linked to two phases of technological and behavioral innovation within the Middle Stone Age of southern Africa - the Still Bay and Howieson's Poort industries - that are associated with early evidence for symbols and personal ornaments. Establishing the correct sequence of events, however, has been hampered by inadequate chronologies. We report ages for nine sites from varied climatic and ecological zones across southern Africa that show that both industries were short-lived (5000 years or less), separated by about 7000 years, and coeval with genetic estimates of population expansion and exit times. Comparison with climatic records shows that these bursts of innovative behavior cannot be explained by environmental factors alone.