whatA lattice of players caught in the prisoner's dilemma: cooperate or defect, then copy whichever neighbour scored best. Cooperation survives as churning clusters inside seas of defection, and the slider decides whether it thrives, hangs on, or is reduced to embers.

whyDefection is always the better move against any one opponent, so why is there cooperation anywhere? Nowak and May's answer needs no memory and no punishment, only space: cooperators win by clumping. This is that model, churning live.

howEach round every player earns points from its eight neighbours: two cooperators each earn one; a defector fleecing a cooperator earns the temptation, the slider. Then each player copies the best scorer around it, itself included. Cooperator clusters enrich their insides faster than defectors can gnaw the rim, and the frontier churns in kaleidoscopic filigree. Cooperators lie flat, defectors lean, fresh turncoats are bold. Click to plant a pocket of the local minority.