  We study a lattice model of ``commons'', where a resource is shared locally
among the agents of various cooperative tendency. The payoff function of an
agent is proportional to the fraction of his operation rate and the net output
of the resource. After each time step a site is occupied by the neighbor of
maximum profit or by its owner himself. In steady state the model is dominated
by ``altruist'' agents with a small minority of selfish agents, forming a
complex pattern. The dynamics selects cooperative levels in a way that the
model becomes critical. We study the critical behavior of the model in case of
moderate mutation rate and find the power spectrum of fluctuation of activity
shows a $1/f^\alpha$ behavior with $\alpha \sim 1.30$. In case of very slow
mutation rate the steady state has slow fluctuations which helps the evolution
of higher cooperative tendency.
