Categorical replies to categorical questions by cross-fostered chimpanzees

The chimpanzees Washoe, Moja, Tatu, and Dar were reared under human cross-fostering conditions that included the use of American Sign Language (ASL) as the medium of two-way communication. In the course of everyday conversation they were asked, in signs, the Wh-questions that are typically asked of young children. In earlier studies, extensive samples showed a pattern of replies, most significantly a developmental sequence, that closely matched the pattern found in the replies of young children. Part 1 of this report is based on a special sample taken when Tatu was 63 months old and Dar was 56 months old, in which experimenters used a large pool of nameable objects, and asked a naming question and at least one descriptive question about the same object in the same context. Tatu and Dar replied to naming questions (WHAT THAT? or WHAT NAME THAT?) with signs that were nouns and to descriptive questions with signs that were modifiers: possessive pronouns for WHOSE THAT?, colors for WHAT COLOR THAT?, and materials for WHAT THAT MAKE FROM? Part 2 is a reanalysis of the Part 1 sample and several other samples of replies, demonstrating that even when their reply was incorrect, these chimpanzees usually replied with a sign from the category specified by the question. The continuities that biologists seek are continuities of laws, patterns of resemblance rather than overlapping data points. Results reported here add depth to the patterns demonstrated in earlier studies.