‘Helical curriculum’ model of social learning of complex skills (educationalists talk of a ‘spiral curriculum’ in which topics are revisited at increasingly higher levels, but representing the developmental time dimension creates a three-dimensional helix, not a two-dimensional spiral). At each turn of the helix, an observer watches a model and learns from them. However, in between such observational episodes is a crucial period of exploration and practice, as a result of which the learner extracts additional aspects in consecutive observational periods a–e, aspects that it could not assimilate earlier. Corresponding skill levels are thence able to rise progressively, indicated by 1–5. (Online version in colour.)