Why did evolution take place? What induced people to give up the ‘original affluent society’ (Sahlins) and to develop †agriculture, *urban life, or the computer? Put in this way, the question is silly; nobody ever chose deliberately to do so, and nobody envisaged such complex phenomena. They came to happen as unforeseen consequences of earlier decisions and choices, most of which were responses to greater or smaller changes in the way of life of peoples. This illustrates again that most evolutionary changes took place unintended, and without specific planning (Hallpike 1986, Ingold 1986). In this respect social or cultural evolution conforms to Darwin’s view that evolution has no direction. Having established this fact, we can try to answer the question of why all kinds of qualitative changes in human cultures occurred; and why-according to Spencer-there is a tendency towards growing complexity.