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The evolution of material culture: insights from orangutans

Carel P. van Schaik, Biological Anthropology and Anatomy, Duke University, Box 90383, Durham, NC 27708-0383, USA

     Human technology evolved from the making and using of feeding tools by non human primates, but the processes leading to this elaboration have been unclear. I present a model that explains why only some great apes show habitual tool use in the wild and why there is so much geographic variation in tool use in chimpanzees and orangutans. An initial test of this model focuses on Sumatran orangutans, in which at least two forms of habitual use of feeding tools occurs and culturally based population-specific behaviors are documented. Geographic variation in tool use in wild orangutans under similar ecological conditions and of varying genetic distance, is documented. The results indicate that aspects of the process by which individuals acquire the skill, i.e. invention and social transmission, must play a decisive role in the geographic incidence and the frequency and form of use within populations. I propose that invention is likely to limit the geographic incidence of tool-using skills, whereas the reliability of social transmission determines the continued ubiquity and uniformity of a skill after it is invented. Evidence for these proposals is presented for orangutans and evaluated for chimpanzees as well. It is concluded that social tolerance is a critical factor in the maintenance of customary or habitual tool-using skills in great ape populations. By implication, increased social tolerance in an ecological context offering frequent opportunities for fitness-enhancing tool use was an important ingredient in the complex of interlinked factors favoring the flourishing of hominid technology and the accompanying cognitive and social changes. It is also tentatively concluded that invention is surprisingly rare in wild great apes and probably in earlier hominids, suggesting that invention has most often been the result of serendipitous coming together of operants and objects rather than insight-driven experimentation. By implication, social cognition (as implied by social learning skills) outpaced physical cognition (as implied by insight learning of novel techniques) during the early phases of hominization.