Reviewer 2's Review (Andy Gardner)

“The problem of public goods is the focus of a huge amount of research interest across multiple disciplines, from biology to economics to sociology and philosophy. The problem is: why should an individual cooperatively contribute public goods, which are shared by everyone, when it could save its own energy and resources and simply 'free ride' on the cooperation of others? Typically, in any analysis of this sort of problem, the payoffs for individuals adopting particular behaviours are usually regarded as a function of the frequencies of the different strategies employed by their social partners. The public goods themselves usually remain implicit. The present ms focuses on what happens to public goods games when the public goods are made explicit and, in particular, when they are durable, so that they reflect past as well as present levels of cooperation. They find that durability leads to interesting transient differences in the dynamics of public goods games and, in some cases, can alter the long-term equilibria too. They also use their formalism to explore the case of 'public bads' such as pollution which, of course, is hugely topical. I have some quibbles with the theoretical formalism (details below), which I feel could be ironed out with a bit of thought. In general, I found this to be a very exciting analysis, and I found the ms very readable. It will be of interest to a wide audience, and the media, and will certainly stimulate much discussion - it would make an excellent contribution to PLoS ONE. ”

N.B. These are the general comments made by the reviewer when reviewing this paper in light of which the manuscript was revised. Specific points addressed during revision of the paper are not shown.