 As usual, the impetus for looking at spatial SPDs seems to come from Axelrod. Four copies of each of the 63 strategies submitted to Axelrod's tournament were arranged on a grid with a spherical geometry so that each cell had four neighbors for both interaction and comparison. For every initial random distribution, the resulting SPD eventually reached a state where the strategy in every cell was cooperating with all its neighbors, at which point no further evolution is possible. In these end-states only about ten of the 63 original strategies remained. The remaining strategies were no longer randomly distributed, but segregated into clumps of various sizes. Axelrod also showed that under special conditions evolution in an SPD can create successions of complex symmetrical patterns that do not appear to reach any steady-state equilibrium.