  We tested the computational feasibility of the proposal that open-ended
cultural evolution was made possible by two cognitive transitions: (1) onset of
the capacity to chain thoughts together, followed by (2) onset of contextual
focus (CF): the capacity to shift between a divergent mode of thought conducive
to 'breaking out of a rut' and a convergent mode of thought conducive to minor
modifications. These transitions were simulated in EVOC, an agent-based model
of cultural evolution, in which the fitness of agents' actions increases as
agents invent ideas for new actions, and imitate the fittest of their
neighbors' actions. Both mean fitness and diversity of actions across the
society increased with chaining, and even more so with CF, as hypothesized. CF
was only effective when the fitness function changed, which supports its
hypothesized role in generating and refining ideas.
