An Experiment in Spontaneous Tool Making Behavior by Captive Chimpanzees

Abstract

The experiment here described constitutes the first step in an attempt to compare spontaneous tool use and tool making in captive chimpanzees and other primates, with a view to elucidate the basis of the more frequent and diverse types of tool use observed in wild chimpanzees. A milk bottle, filled up to 3 cm. with fruit juice was secured outside the cage within reaching distance of two young female chimpanzees (7 year old). Foliage was provided in the cage as a potential material for sponge making. The uses of foliage for absorbing and drinking juice were observed. Experiments, lasting 1 hour each, were repeated 21 times over a period of 4 months. A stepwise progression was seen in the successively appearing behaviors : from introducing leaves in the bottle, withdrawing them with a finger and licking, to the use of twigs of various lengths and finally to the munching of the extremity of a branch into spongelike condition. Nevertheless, it is important to notice that new modes of tool use did not replace earlier and less efficient ones. Also, though a newly discovered particularly efficient mode of tool use tended to be practiced intensively at the beginning of the next session, in general various of tool use appeared in any given order, regardless of their order of invention. Though the stepwise progression in the use and modification of the available material would seem to indicate that the animal acquired steadily a more accurate grasp of the situation and aimed at the production of increasingly efficient drinking tools, the apparently random alternation of various modes of tool use fails to support this interpretation. Comparison with a similar experiment undertaken by LETHMATE (1976) with young orangs reveals overall similarities and some differences partly due, perhaps, to the slightly different experimental setup.