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.
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