 In this case, there are two aspects to the emergence of cooperation in the form of Tit for Tat. One is the fact that play is local: strategies total points over just local interactions, rather than play with all other cells. The other is that imitation is local as well: strategies imitate their most successful neighbor, rather than that strategy in the array that gained the most points. The fact that both conditions play out in the local structure of the lattice allows clusters of Tit for Tat to form and grow. In Axelrod’s tournaments it is particularly important that Tit for Tat does well in play against itself; the same is true here. If either game interaction or strategy updating is made global rather than local, dominance goes to All Defect instead. One way in which cooperation can emerge, then, is through structured interactions (Grim 1995; Skyrms 1996, 2004; Grim, Mar, &amp; St. Denis 1998). Alexander (2007) offers a particularly thorough investigation of different interaction structures and different games.