 The description of the “neither” move and “opt-out” payoffs varies somewhat in accounts of the optional PD. For Kitcher they frequently represent a choice to “go solo.” For example, a baboon, rather than thoroughly or sloppily grooming a partner in exchange for being groomed thoroughly or sloppily by its partner, may choose to groom itself. Often, on the other hand, it is suggested is that \(\bN\) represents a choice to “sit out” the game, perhaps in order to obtain a more suitable partner with whom to play later. The significance of this difference, if any, will emerge in iterated and evolutionary versions of the game. (See sections 11–17 below.) Those who write about the optional PD often express the hope that it might provide a suitable model to investigate the idea that cooperation can be achieved if agents select the partners with whom they interact. That idea is modeled somewhat differently, and perhaps more directly, in Social Network Games discussed in  section 19  below. Further discussion of the idea is left to that section.