Simon A. Levin has an interesting article about the sources of social cooperation in human societies and in other animals. He reminds us several times across the article that Hardin (the first author to analyze the "tragedy of the commons") argued that the solutions to commons problems involve mutual coercion, mutually agreed upon: "Mutual coercion, mutually agreed upon, has been successful over and over again in small societies. Arrangements such as the lobster gangs of Maine, the water temples of Bali, and the Tribunal de las Aguas de Valencia, all give evidence that self-organized solutions, with emergent norms, can help protect public goods, combining top-down and bottom-up mechanisms. As we move to larger scales, however, for example in protecting climate or biodiversity as public goods, the challenges become greater. Recent work demonstrates the importance of great inequities in wealth, and of heterogeneity more generally in addressing global problems. These issues of scale and heterogeneity led the late Ostrom to argue for a modular, polycentric approach to addressing climate change, which means starting locally, and building up from there. And I would argue that it also means agreements between subsets of nations, as building blocks for larger-scale agreements; indeed, from what we know about Darwinian selection and the evolution of multicellularity, in which modules can become building blocks for emergent complexity, this seems the most hopeful approach to global sustainability. The greatest challenges to achieving a sustainable future in an increasingly interconnected world rest in finding solutions to dealing with public goods and common-pool resources, especially when the individual agents are nations or distributed networks of individuals. The lessons to be derived from evolution and evolutionary theory are a starting point, but scaling up to larger and larger groups, in a technological world in which individuals can make sophisticated calculations about their futures and their interests, create novel challenges, both from the viewpoints of applications and mathematical theory. Addressing such challenges is essential if we are to address our own futures, and represent some of the most exciting challenges for sustainability science." Levin believes that consensus building may be more important than voting, in a paragraph where he could have cited the great Swedish economist Knut Wicksell: "Of course, the theory of how societies vote and how they should vote has been a staple of economics and the decision sciences for many decades. In most situations, however, the way human groups arrive at collective decisions is much more bottom-up, based on a balance between innate tendencies and knowledge on the one hand, and imitation on the other. What then is the role of leadership? How is consensus achieved in democratic societies, and how important are those who are more likely to follow than lead?"