Chess and Chaos Theory

From "IPD-Spatial chaos" at Another Blog:

Consider a population of players distributed on the squares of a chess board. Each player interacts only with its immediate neighbours, obeying the parameters of the single-shot Prisoner's Dilemma. In the next generation, the square is inhabited by the player who scored the highest total: neighbour or previous owner. Obviously, a single cooperator perishes, but just four cooperators in a cluster can get a foothold, since each interacts with more cooperators than a defector can reach.

Huh?!?