The appearance of modern human behaviour is poorly explained in terms of the biological evolution of the human brain and its increased cognitive capacity.
The graphics below were first published in 'Science' in 2009, and showed that demography is a major determinant in the maintenance of cultural complexity and that variation in regional subpopulation density and migratory activity results in spatial structuring of cultural skill accumulation.
Each circle represents a sub-population, and its diameter represents its skill level (Z). Unseen in the graphic is a stochastic process of migration of individuals between sub-populations. A parameter for skill loss from imperfect learning was incorporated. Also incorporated in the model was a parameter for errors in the transmission of information during learning which mostly leads to the degradation of the skill but occasionally can result in an improvement, much like a genetic mutation occasionally results in an increase in fitness for the individual.