As man does not live in a solitary state, habits and feeling develop within him which are useful for the preservation of society and the propagation of the race. Without social feelings and usages life in common would have been absolutely impossible. It is not law which has established them; they are anterior to all law. Neither is it religion which has ordained them; they are anterior to all religions. They are found amongst all animals living in society. They are spontaneously developed by the new nature of things, like those habits in animals which men call instinct. They spring from a process of evolution, which is useful, and, indeed, necessary, to keep society together in the struggle it is forced to maintain for existence.

II - Law and Authority (1886)