The jaw movements of speech are most probably derived from jaw movements associated with vocalisation. Cyclicity does not argue strongly for derivation from a cyclic pattern, because it arises readily in any system with feedback control. The appearance of regular repetition as a part of ritualisation of a display may have been important.

Presents a review of all the main aspects of work on learning and plasticity in behaviour and neural mechanisms in the chick, together with related topics such as the development of behaviour and lateralization of function.