 In iterated and evolutionary versions of the optional PD, we imagine that players from some population are repeatedly paired off and given the opportunity to play the PD (choosing either \(\bC\) or \(\bD\)) or to opt out (choosing \(\bN\)). In choosing \(\bN\), a player forgoes the opportunity of receiving the reward or temptation payoffs until the next pairing. In most human interactions that come to mind, a refusal to engage with a particular partner does not represent quite the same loss of opportunity to engage with another as a choice to engage does. If I buy a car from an unscrupulous dealer, I'll have to wait a long time before my next car purchase to do better; but if I refuse to engage with her I can immediately begin negotiating with a neighboring dealer. Nevertheless, there may be situations among people (and more likely among non-human animals or among nations or corporations) that are appropriately modeled by evolutionary versions of the optional PD.