This is why in the immediate wake of great disasters—a flood, a blackout, a revolution or economic collapse—people tend to behave the same way, reverting to a kind of rough-and-ready communism. Hierarchies, markets and the like become luxuries that no one can really afford them. Anyone who has lived through such a moment can speak to the way strangers become sisters and brothers, and human society itself seems to be reborn. We are not just talking about cooperation.