The Ontogeny of Chimpanzee Gestural Signals: A Comparison Across Groups and Generations

Observations of the gestural communication of two groups of captive chimpanzees are reported. For one group the observations represent a fourth longitudinal time point over a 12 year period; the other group was observed for the first time. There were two main questions. The first concerned how young chimpanzees use their gestures, with special foci on the flexibility displayed in signal use and on the sensitivity to audience displayed in signal choice. It was found that chimpanzees are very flexible in their signal use (different signals for same goal, same signal for different goals) and somewhat sensitive to audience (signal choice based on attentional state of recipient). The second question was how chimpanzees acquire their gestural signals. Comparisons between the two groups showed much individual variability both within and between groups. In addition, when each of the two contemporary groups was compared with the previous longitudinal time points for one of the groups, no differences in concordance were found. It was concluded that youngsters were not imitatively learning their communicatory gestures from conspecifics, but rather that they were individually ritualizing them with one another in social interaction. An experimental study in which two individuals were taught new gestures and returned to their groups — with no subsequent signs of imitation — corroborated this conclusion. Implications of the current findings for the understanding of chimpanzee communication and social learning are discussed.