variable for both cases: the average fraction of steady state cooperators, with the average taken over the whole population. But it must be recalled that for populations with small numbers of initial cooperators the variable does not give atypical value of final cooperators because the steady state cooperators distribution has at least two modes clearly separated, one with zero cooperators and other with many cooperators. We have used this variable to show that for some stochastic dynamics the results are very similar to what has been described above for a deterministic dynamics. In the stochastic dynamics we have used, the agents choose the strategy of a neighbor with a probability proportional to the corresponding cumulative payoff, but only if it is larger than his/her own cumulative payoff [@oht]. Fig. \[figstoch\] shows some results for this dynamics. Curves for several different values of $t$ are shown because in this case, the dependence on $t$ is not as simple as in the deterministic case. In any case, several qualitative similarities with the deterministic case are apparent. For $\rho=0.5$ the ordered networks are more favourable to cooperation than completely disordered ones, at least for $t \leq 1.15$. For $\rho=0.1$ the situation is reversed, 