 In the dynamic PD where interaction is random (i.e., there’s no correlation), defectors do better than the population average as long as there are cooperators around. This follows from the fact that, as we saw in  Section 2.4,  defection is always the dominant strategy in a single game. 100% defection is therefore the ESS in the dynamic game without correlation, corresponding to the NE in the one-shot static PD.