Abstract # 236:

Scheduled for Friday, August 10, 2001 11:00 AM-12:00 PM: (Fine Arts Auditorium) Oral Presentation


C. van Schaik
Biological Anthropology & Anatomy, Duke University, Box 90383, Durham, NC 27708
     Among primates, extensive tool use for subsistence is found mainly in two great ape species, chimpanzees and orangutans, but in both of them the nature and variety of the tools shows remarkable geographic variation. Detailed comparisons of different orangutan populations indicate that genetic or ecological factors alone cannot account for the distribution of tool use, supporting the interpretation that the presence of these geographic variants is limited by developmental factors. Hence, these geographic variants are traditions (as are, potentially, many other, geographically non-varying behaviors). Of course, similar conclusions were reached for chimpanzees before. To explain geographic variation in the size of tradition repertoires, I examine the Opportunities-for-Social-Learning model, which assumes that socially protected individuals are more likely to invent novel techniques and also more likely to acquire them through observational learning from a skillful individual. The model predicts that the amount of social tolerance during foraging predicts the number of complex foraging skills, and especially the tool kit, present in a population. Evidence for this prediction is presented for various orangutan populations in the coastal swamps of northwestern Sumatra, as well as in a test of individual variation in tool-use propensity within one social unit. A comparative test using chimpanzee data also supports the prediction. It is concluded that social tolerance is a critical factor in the maintenance of learned skills in great ape populations. I will discuss the implications of these findings for our understanding of the evolution of human culture, and for orangutan conservation.