Defect is a strictly dominant strategy in the Prisoner's Dilemma, making Cooperate a strictly dominated strategy.

This can be seen in a particularly stark form in figure 6, above. In the case of the Prisoner’s Dilemma, if the population begins in the state where everyone cooperates, the replicator dynamics will remain in that state forever, because the strategy of Defect cannot be introduced. This shows that, under the replicator dynamics, there can be instances where even strictly dominated strategies will persist.