Duane Rumbaugh, Sue Savage-Rumbaugh and Bill Fields
An overview of language research with apes during the last 50 years provides strong evidence for their use of words (manual gestures or graphic patterns) as meaningful symbols that refer to things and their qualities (temperature, color, etc.) persons or peers, activities, or as places for foods, rest, chasing, and so on.
Apes can also comprehend new sentences with fairly complex structures. They can use language to achieve outcomes that they would otherwise not be able to achieve, for example to formulate names for new items based on novel word combinations. They can use manual signs and graphic symbols to communicate about things that are not present; they can learn to communicate their needs and to fulfill one another’s requests for specific tools, foods, and games; they can integrate their language skills and apply them creatively even several years later in new contexts. If reared in a manner that approximates child rearing, apes can come to understand complex human speech and its syntax.
Language acquisition using lexigrams is optimized if it occurs in the course of social rearing in an environment that is language structured. Ideally, this provides a running vocal narrative to the apes as infants, describing what things are, what is about to happen, and so on; this narrative should be integrated with the use of graphic symbols that are to function as words. Results show that apes can enter the language domain as a result of human rearing and instruction, although their capacity for language is much more limited than that of humans. A great deal remains to be learned. Future research promises to continue to blur the boundary between the basic principles of human and animal learning, language, symbolic function, and complex behaviors.
The following summaries of three significant research projects in the study of the cognitive development of primates are excerpted from Animal Bodies, Human Minds, by W.A. Hillix and Duane Rumbaugh (Kluwer Academic/Plenum Publishers, 2004).