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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

Teasing Out the Truth

The hypothesis offered above is a mix of fact and fiction, imaginative storytelling based on disparate datasets, some of which are better constrained than others. But it is consistent with computer simulations carried out by Stephen Shennan of University College London in 2001 that posit that cultural innovations are more likely to be kept and shared in larger rather than smaller populations. Periods of population expansion would be more likely to produce successful transmissions of technological and behavioral innovations—such as those associated with the Still Bay and Howieson’s Poort. And such novelties would likely have been lost when populations shrank and became isolated. If cultural differences developed among segregated populations, then recent model simulations suggest that migration between groups would have been discouraged and demographic growth further impeded. The rise and fall of the Still Bay and Howieson’s Poort may most likely be linked, therefore, with the demographic history and social fabric of our hunter-gatherer ancestors.

The challenge before us now is to transform speculative claims into robust inferences. The quest to understand the emergence of modern human behavior and our ancestors’ dispersal from Africa will require insights from archaeology, ecology, genetics, linguistics and climate science. There is also a clear need for reliable dating of key archaeological, genetic, demographic and environmental events, and the placement of each on a more finely resolved and standardized timescale. At present, we cannot explain the population expansion of the L3 haplogroup in sub-Saharan Africa as the direct outcome of any particular environmental event. In fact, the timing of climatic and demographic changes is too imprecise to confidently plot them in correct chronological order. Perhaps it was a spark of human ingenuity among a group of L3 carriers in East Africa that was the catalyst for cultural innovation. And perhaps that innovation encouraged social cohesion and the more efficient use of natural resources, prompting rapid population growth among this group of people. This population expansion may have, in turn, promoted more innovations—including the Still Bay and Howieson’s Poort in southern Africa—and the migration of people out of Africa to the north. A crucial next step is to resolve the timing of the main cultural phases in North and East Africa with a precision similar to what has been accomplished for southern Africa. We must position all of these archaeological turning points on the same chronological yardstick with the major climatic, genetic and demographic events on the continent. By arranging events in the correct sequence on the same time line, it may be possible to establish cause and effect—action and reaction—and produce a more informed model of modern human prehistory.


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