The conditions for tool use in primates: implications for the evolution ofmaterial culture

In order to identify the conditions that favored the flourishing of primate tool use into hominid technology, we examine inter- and intraspecific vari ation in manufacture and use of tools in extant nonhuman primates, and deve lop a model to account for their distribution. We focus on tools used in ac quiring food, usually by extraction. Any model for the evolution of the use of feeding tools must explain why tool use is found in only a small subset of primate species, why many of these species use tools much more readily in captivity, why routine reliance on feeding tools is found in only two sp ecies of ape, and why there is strong geographic variation within these two species. Because ecological factors alone cannot explain the distribution of tool use in the wild, we develop a model that focuses on social and cogn itive factors affecting the invention and transmission of tool-using skills . The model posits that tool use in the wild depends on suitable ecological niches (especially extractive foraging) and the manipulative skills that g o with them, a measure of intelligence that enables rapid acquisition of co mplex skills (through both invention and, more importantly, observational l earning), and social tolerance in a gregarious setting (which facilitates b oth invention and transmission). The manipulative skills component explains the distribution across species of the use of feeding tools, intelligence explains why in the wild only apes are known to make and use feeding tools routinely, and social tolerance explains variation across populations of ch impanzees and orang-utans. We conclude that strong mutual tolerance was a k ey factor in the explosive increase in technology among hominids, probably intricately tied to a lifestyle involving food sharing and tool-based proce ssing or the acquisition of large, shareable food packages. (C) 1999 Academ ic Press.