In cross-fostering, the offspring of one genetic stock are reared by foster parents of a different genetic stock to study the interaction of genetic and environmental factors in the development of behavior. From 1966 to 1981, Drs. Beatrix and Allen Gardner recorded the behavioral development of five chimpanzees that were being reared under human cross-fostering conditions. In earlier studies, the human foster- families spoke English to the infant chimpanzees, none of which learned more than four words. What is unique about the Gardners' laboratory was the use of American Sign Language combined with continuous treatment of the chimpanzees as children are treated. Under these conditions, the chimpanzees Washoe, Moja, Pili, Tatu, and Dar learned to use the signs of ASL in ways that resemble the early development of human children, and reached levels far beyond those expected on the basis of earlier linguistic theory. Their behavioral development was recorded with a diary record, systematic samples, controlled experiments, and motion- picture film and video records. The Gardners' present objective is to transcribe, index, and annotate the first two years of the diary record of each of these five chimpanzees. The record of development that results will be the basis for comparisons among the four individual chimpanzees that were cross- fostered from birth (Moja, Pili, Tatu, and Dar), between these chimpanzees and one that was introduced into the cross-fostering environment when she was one year old (Washoe), and between the cross- fostered chimpanzees and chimpanzees reared in the wild and in laboratory cages. Preliminary work on diary transcriptions shows that the planned analyses are feasible. First, orderly sequences of development can be described, since there are consistencies among the cross-fostered chimpanzees in the order of appearance of behaviors of a given type, such as rolling over, crawling, sitting alone, and standing unsupported on two feet. Second, there are individual differences in rate of development; the most precocious chimpanzee in posture and locomotion was also the most precocious in manipulative skills and in communication. And third, many items of behavior described for young children can be found in the records of the cross-fostered chimpanzees: perceptual-motor behaviors, such as visually directed reaching; attachment behaviors, such as using the caretaker as a base for exploring; and communicative behaviors, such as pointing and negative headshakes, as well as the first 50 ASL signs. This research concerns the effects of environmental enrichment on infant chimpanzees. The special rearing conditions enable the Gardners to study, in addition to the development of two-way communication with signs, such aspects of behavioral development as locomotion, observational learning, manipulative skills, and social play. Since intellectual, social, and linguistic development are intimately related, such studies widen and enrich the analysis of the developmental process. The processes that underlie precocity, retardation, and the ultimate level of development are of concern to psychologists, biologists, and anthropologists.
