Public goods interactions (N = 3) in spatially structured populations with punishment but without reputation. Adding punishment opportunities after every public goods interaction leads to rather dramatic changes in the systems dynamics: instead of co-existence one obtains bi-stability. This means co-existence of cooperators and defectors is no longer possible and the initial configuration determines whether cooperation or defection reigns in the long run. Moreover, the parameter range rendering cooperation feasible became much larger.

Somewhat puzzling remains the fact that punishment can actually enforce cooperative behavior even if a population would be better off without such social interactions. In other words, punishment can force people to contribute to a public good even if the return of the public good is less than the contributions.