abstract reasoning By as early as 200,000 years ago hunters in Africa, the Middle East, and Europe had begun hafting stone points onto the ends of their spears (1⇓–3). This marked a significant step in the history of technology, for it was the first time that hominins had united separate elements into a single tool. Indeed, these compound tools actually consisted of three distinct elements: the point, the shaft, and the haft itself. It was the haft that was the challenge because it had to withstand significant impact forces when the spear was used. Many archaeologists consider the development of hafting to mark a major watershed not just for technology, but for the human mind itself (4). But just what is required, in a cognitive sense, to be able to haft a point to a shaft? In this issue of PNAS, Wadley et al. (5) set out to answer this question by duplicating one such hafting technology, identifying the procedures and knowledge required, and arguing that abstract reasoning was an essential prerequisite. In doing so they provide a good example of a relatively new perspective in paleoanthropology—that of cognitive archaeology. How can archaeologists structure a persuasive argument about cognition in the evolutionary past? After all, archaeological data consist of the refuse of hominin activities—broken and abandoned tools, the detritus from tool making, discarded remains of meals, ash from fires, and so on—all disturbed by subsequent activities and natural processes. The answer is that an argument in cognitive archaeology must invariably be based on a sequence of inferences, each of which must be explicit and persuasive if the argument as a whole is to be credible. Fig. 1 is a diagram that summarizes the argument of Wadley et al. that the hafting of spear points with multicomponent glue required abstract reasoning. The organization of the diagram is borrowed loosely from Bothas (6) detailed critique of an archaeological argument for the use of syntactical language by people at Blombos Cave 77,000 years ago (7). The upper row summarizes an idealized sequence of inferences, from prehistoric artifact to cognitive prerequisite, and the lower row, the specific argument of Wadley et al.
Posted on: Wed, 26 Mar 2014 18:09:31 +0000
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