"[Exchange] is common to all men, and to be found in no other race of animals, which seem to know neither this nor any other species of contracts. Two greyhounds, in running down the same hare, have sometimes the appearance of acting in some sort of concert. … This, however, is not the effect of any contract, but of the accidental occurrence of their passions in the same object at that particular time. Nobody ever saw a dog make a fair and deliberate exchange of one bone for another with another dog. Nobody ever saw one animal by its gesture and natural cries signify to another, this is mine, this is yours; I am willing to give this for that."
— Adam Smith, The Wealth of Nations, quoted by Luc Boltanski & Laurent Thévenot in On Justification, 47