This is presumably also why in the immediate wake of great disasters--a flood, a blackout, or an economic collapse--people tend to behave the same way, reverting to a rough-and-ready communism. However briefly, hierarchies and markets and the like become luxuries that no one can afford. Anyone who has lived through such a moment can speak to their peculiar qualities, the way that strangers become sisters and brothers and human society itself seems to be reborn. This is important, because it shows that we are not simply talking about cooperation. In fact, communism is the foundation of all human sociability. It is what makes society possible.