A second and completely different perspective on human cognitive evolution has been taken by Thomas Wynn (1979,1981,1985), who applied Jean Piaget's model of ontogenetic developmental stages in children's object behavior to Lower Paleolithic artifacts and thereby to human phylogeny. The first developmental stage, young infants' sensorimotor intelligence, characterized by pure activity-based intelligence without inner representations of the actions, can also be observed in primate tool behavior; in this stage, activity cannot be reasoned out in advance. The second stage, preoperational intelligence, is marked by inner representations of single consecutive tasks, so that anticipation of the results of an action is limited to the change in only one variable at time; planning of an action is therefore restricted to trial and error. Wynn (1981) has identified this stage in chimpanzee tool manufacture, as well as in the simple technology of Oldowan core tool assemblages (for the problems of Oldowan interpretation see (8.2).
The next stage, the concrete-operational phase, allows coordination of changes in several variables. It is now possible to anticipate the result of an operational sequence or to construct the operational sequence for reaching a desired result, so complex planning can proceed, and errors can be envisioned and corrected before they are executed. This concrete-operational stage, which according to Piaget should be fully developed by age 11-13, is identified by Wynn (1979) in the bifacial technology of Acheulian hand axes. Diverging from Piaget (1970), who differentiated between concrete-operational intelligence in children and the formal-operational intelligence that succeeds it in modern adults, Wynn merges these two stages and concludes that human phylogenetic development of cognition—as it can be seen from technological perspective—reached modern competence around 300,000 years ago, at the latest. Although Wynn's interpretation needs reevaluation in light of challenges to Piaget's theory by modern psychology, his attempt to adapt an object-directed psychological theory to archeological analysis of artifact traits is a positive example for future studies.
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