Long-term data on the occurrence of “teasing” in young chimpanzees living in the Arnhem Zoo chimpanzee colony are presented. They strengthen the hypotheses—presented in earlier papers—concerning the existence of two functional forms of this so-called quasi-aggressive behaviour and provide insight into the way in which they develop. Developmental changes are visible both in the performance of quasi-aggressive behaviour and in the effects evoked by the behaviour. The purpose of the reducing uncertainty type of quasi-aggressive behaviour, performed by male and female youngsters towards adult females, is to obtain more predictable responses. As youngsters grow older, they engage in this behaviour also to gain control over the responses of the target animals. Eventually, the quasi-aggressive behaviour of male youngsters develops into adult-like bluff and attack behaviour the purpose of which is to establish dominance relationships. The investigating authority type of quasi-aggressive behaviour, directed towards adult males, is associated increasingly with the exercise of power by the target males. The youngsters increasingly behave submissively towards the males and direct quasi-aggressive behaviour especially towards the alpha-male at moments when he is bluffing or involved in other conspicuous social interactions. These and other changes in the relationship between adult males and male youngsters are already visible well before the onset of puberty in the youngsters.
It is discussed in how far the development of these exploratory aggression types involves social learning processes and how this fits in with current concepts concerning the development of aggressive behaviour.