Fluctuating efforts and sustainable cooperation

We show that when individuals confronted with a social dilemma contribute to the common good with an effort that fluctuates in time, they can make the group generate an average utility that actually decreases in time. This paradoxical behavior takes place in spite of the fact that typically individuals are found to be contributing at any given time. This novel phenomenon, which we verified in a number of computer experiments, is the result of an intermittent effect, whereby unlikely bursts of defection determine the average behavior of the group. Besides providing a dynamical theory for the lognormal distribution found in some sociological data, these results show that the typical behavior of individuals comprising a group can be inconsistent with its average properties.