In this paper the notion of "state of nature" is interpreted in the light of Elliot Sober's "equilibrium explanations". An equilibrium explanation explains a state of affairs X (e.g. the 1:1 sex ratio in animal populations with sexual reproduction) by showing that X is a unique stable rest point in a suitable dynamics. According to this interpretation, any "state of nature" theory explains the existence of a given rule or institution X (e.g. the state) by showing (a) that X is an equilibrium (in game theoretical sense), and (b) that any interaction among individuals not regulated by X is a disequilibrium state of affairs. In the second part of the paper, some related issues raised by multiplicity of equilibria and oscillatory or chaotic behaviour are also discussed.