A third means used to illuminate the phylogenetic dimension of the cognitive basis of early human tool behavior has been to make comparisons with ape performance. In the last years, the knowledge of tool behavior in great apes has markedly broadened through research on chimpanzees Pan troglodytes (McGrew 1992; Whiten et al. 1999) and orangutan Pongo pygmaeus (van Schaick et al. 2003), as well as on the less-observed bonobo Pan paniscus (Hohmann and Fruth 2003). Probable cultural differences among groups have been compiled and correlated with complex object-behavior, and these data have expanded arche-ologists' view of the range of culturally influenced behavior and artifact categories not preserved in archeological context. As noted previously, however (Section Definitions), primatological results answer archeological questions about basic object behavior only partially.
To fill this gap, which is especially critical with regard to stone tool technology, experiments have been designed to examine motor and cognitive abilities in stone flake production. While early testing with an orangutan (Wright 1972) had a behavioral focus for understanding the functional aspects of cutting tools, the long-term experiments with bonobo Kanzi (Toth et al. 1993; Schick et al. 1999) have been planned in cooperation with archeologists and observed from a technological perspective. Kanzi proved able to detach flakes from a core with a hammerstone, although he preferred to produce cutting edges by throwing a stone on a hard surface, a technique he invented himself. After 3 years of knapping experience, Kanzi could still not flake efficiently by exploiting acute angles on the core, a method regularly observed in Early Lower Paleolithic context (Roche et al. 1999).
Archeologists have also analyzed and compared the stone tools at a chimpanzee nut-cracking site with Oldowan assemblages (Mercader et al. 2002). These comparisons suggested that, despite previous doubts (Wynn and McGrew 1989), morphological analysis could clearly discriminate between human tools flaked intentionally and chimpanzee artifacts produced as a chance result of other activities with stones. Primate archeology is still in its beginnings and has not yielded any model of human cognitive evolution; nonetheless, it is another promising approach for taking a detailed look at the specificity of human tool behavior.
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