Report for SAGA2/COE Symposium

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

Adult male (Avno - the dominant resident male in Suaq Balimbing
(C) Perry van Duynhoven - Wildlife Conservation Society

Human technology evolved from the making and using of feeding tools by nonhuman primates, but the reason for this explosive elaboration has been unclear. Because human technology is so far beyond the tool use of other primates that it can be called unique it is difficult to find nonhuman primate referents for this phenomenon. However, there is much geographic variation in tool use in chimpanzees. Likewise, Sumatran orangutans at Suaq Balimbing, a coastal swamp site, show at least two forms of habitual use of feeding tools, whereas subsistence tool use is absent among other known orangutan populations. Any explanation of this geographic intraspecific variation is likely to explain the first thrust toward hominid technology. Comparative data on tool use geography in northern Sumatra show that ecological and genetic factors are involved as necessary preconditions, but that the geographic variation is cultural, as in chimpanzees. Thus, the incidence of skilled behaviors such as tool use in a social unit must be explained with reference to the ontogenetic process of skill acquisition: invention, diffusion (importing skills invented elsewhere) and social transmission.
I present the Tolerant Gregarious Foraging model to account for this geographic variationin the number of skillful feeding techniques, in particular tool use, in dextrous extractive foragers such as great apes. This model proposes that social factors affect the likelihood of invention, and especially successful diffusion and transmission of a particular skill such as tool use, and hence its maintenance in a population. It 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. Initial tests of these assumptions are quite favorable, suggesting that the hypothesis has potential. 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. The prediction is also upheld in a preliminary test of individual variation tool-use propensity within one social unit. Comparative data on chimpanzee sites (Whiten et al., 1999) are used to test the prediction for the great apes with the most extensive data. Measures of tolerance provide a highly significant prediction for the number of customary or habitual subsistence tools used in different chimpanzee populations, as well as the number of skillful subsistence techniques, whether common or not, found in each population. It is concluded that social tolerance is a critical factor in the maintenance of tool-using skills in great ape populations.

Broken Neesia fruits - in an area east of the Alas river orangutans do not use tools and have to break open the fruits (with considerable effort) to get at the well-protected, nutritious seeds. As Suaq Balimbing, and a few more sites, orangutans use tools to get the seeds out of the fruits.
(C) Perry van Duynhoven - Wildlife Conservation Society

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. Although the exact causes for this increased tolerance are not known, they could be related to larger group size or cohesion or to ecological changes producing more food sharing and exchange. The strongly reduced canine size of australopithecines, as well as later hominids, relative to extant great apes, suggest a clear reduction in the frequency of escalated physical dyadic contests. It is concluded that technology is critically dependent on the proper social structure, and that even brief breaks in these appropriate social conditions can spell the return to the simplest possible levels of technology.