Developmental systems (1/11) are provided with an autotelic mechanism for driving their development. An autotelic component (1) in the system uses a mapping mechanism (2) to produce an output based on a set of inputs. The mapping mechanism (2) implements a mapping that is dependent upon a state associated therewith. The content of the state is changed by a learning/repair module (3) based on interactions between the system and the environment, and so reflects knowledge gained by this component as a result of its experience. The autotelic component (1) monitors its own performance with reference to the level of a set of one or more challenge parameters whose levels quantify the complexity of different parameters relating to the autotelic component (1). The state associated with the mapping mechanism 2 is altered depending upon the component's performance as evaluated during the monitoring. A controller (5) controls the levels of the challenge parameters.