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Human History Written in Stone and Blood

Two bursts of human innovation in southern Africa during the Middle Stone Age may be linked to population growth and early migration off the continent

Zenobia Jacobs, Richard G. Roberts

Catalysts of Creativity

Figure 6. Comparison of multiple sites' age estimatesClick to Enlarge ImageAnswers about the ages of these artifacts, of course, lead only to more questions. What stimulated the Still Bay and Howieson’s Poort industries? Why did they last so briefly and end so abruptly? And what was responsible for their—in archaeological terms—instantaneous appearance and subsequent disappearance across a vast expanse of southern Africa? Human responses to environmental change have long intrigued archaeologists, so climate change must top the list of suspects. The last interglacial/glacial cycle stretched from about 130,000 to 12,000 years ago, which includes the time span of the Still Bay and Howieson’s Poort. During this period, southern Africa experienced marked changes in temperature and precipitation associated with global changes in ice volume, sea level and patterns of oceanic and atmospheric circulation. The timing and magnitude of these climatic fluctuations have been detected by international climate research groups in the pattern of change in the ratio of oxygen isotopes (and the concentration of atmospheric greenhouse gases) in ice cores retrieved from Greenland and Antarctica. These records share many general features, but the Southern Hemisphere climatic records from Antarctica are the most relevant to southern Africa.

There are uncertainties involved in extrapolating from one continent to the other, and there are some differences in the timing and amplitude of changes among the various Antarctic records. But neither obscures the overall picture: the Howieson’s Poort occurred during a period of climatic warming, whereas the Still Bay cannot be confidently assigned to either a warming or a cooling interval. The fact that the same climatic conditions do not appear to have prevailed during these two episodes of innovation suggests that their emergence and their demise were not driven by a common environmental cause. The lack of correlation between symbolic human expression and a particular type of shift in climate does not preclude the possibility that climatic fluctuations influenced where and when people occupied or abandoned rock shelters. On the contrary, given the lifestyle of hunter-gatherers, the best sites for habitation and access to resources surely changed over time, in concert with environmental changes. In fact, our data hint at the preferential occupation of rock shelters during generally warmer intervals; perhaps more open-air sites were favored at other times.

Figure 7. Age estimates plotted against Antarctic dataClick to Enlarge ImageTwo further lines of evidence challenge the view that the rise of Still Bay and Howieson’s Poort can be explained simply as responses to environmental factors alone. First, these industries are found in diverse climatic and biogeographic contexts, yet they appeared and disappeared around the same times at various sites. Such synchronicity would not be expected if only certain environmental conditions were conducive to their launch and spread. Second, the Howieson’s Poort was followed by three separate periods of much less sophisticated stone-tool making known as the post-Howieson’s Poort, the late Middle Stone Age and the final Middle Stone Age. No personal adornments or symbolic renderings contemporary to those periods have been found. The latter pair of cultural phases, and possibly the post-Howieson’s Poort, flourished during periods of relative warming—as did the Howieson’s Poort—yet none of them boasts any technological or behavioral innovations. When viewed in this broader context, therefore, the flaring of symbolic behavior during the Still Bay and Howieson’s Poort periods cannot be linked exclusively to a warm, cool or transitional climate.

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