INTRODUCTION

Chimpanzees have long been famous for their tool use in the wild (Goodall, 1964), as well as in captivity (Köhler, 1927). Orangutans are now known to use tools in the wild (Van Schaik, Fox & Sitompul, 1996) as well as in captivity (Lethmate, 1982). Even bonobos, who are not known to use tools in the wild (Kano, 1986), are widely known for their tool use in captivity (Savage-Rumbaugh & Lewin, 1994). Of the great apes, only gorillas have been described as rarely using tools in captivity (McGrew, 1992), as well as never using tools in the wild (Schaller, 1963). In his review of tool use in great apes, McGrew (1992) cites only one report of tool use – use of a stick to rake in food – in captive gorillas. The idea that gorillas lack problem-solving capacities traces back to Yerkes' study of the gorilla Congo (Yerkes, 1927). Recently, this idea was reinforced by a study of the development of tool use in an infant gorilla (Natale, 1989)

On the other hand, at least two factors suggest that gorillas should be capable of tool use. First, gorillas display 5th- and 6th-stage sensorimotor cognitive abilities similar to those of other great apes (Chevalier-Skolnikoff, 1977; 1983), and tool use – at least, purposeful use of a variety of tools to solve problems – is an index of 5th-stage sensorimotor intelligence similar to that of 2–year-old human children (Piaget, 1952). Second, orangutans, gorillas, chimpanzees, bonobos, and humans are closely related sister species that share a common ancestor roughly dating back 14 to 18 million years ago (see Begun, this volume).