Before revision:  In addition, mutation, in combination with heterogeneous updating rules, also diminishes co-operators, a phenomenon that is prominent when a large proportion of the population consists of imitators rather than adopters of aspiration-based updating.
After revision:  In addition, mutation, in combination with heterogeneous updating rules, also diminishes cooperators. This phenomenon is prominent when a large proportion of the population consists of imitators rather than adopters of aspiration-based updating.