But there has also been a great change in human conditions due to a change in the spirit of human life. This change has gone on side by side with the increase and extension of knowledge, and is subtly connected with it. There has been an increasing disposition to treat a life based on the common and more elementary desires and gratifications as unsatisfactory, and to seek relationship with and service and participation in a larger life. This is the common characteristic of all the great religions that have spread throughout the world in the last twenty odd centuries, Buddhism, Christianity and Islam alike. They have had to do with the spirit of man in a way that the older religions did not have to do. They are forces quite different in their nature and effect from the old fetishistic blood-sacrifice religions of priest and temple that they have in part modified and in part replaced. They have gradually evolved a self-respect in the individual and a sense of participation and responsibility in the common concerns of mankind that did not exist among the populations of the earlier civilizations. The first considerable change in the conditions of political and social life was the simplification and extended use of writing in the ancient civilizations which made larger empires and wider political understandings practicable and inevitable. The next movement forward came with the introduction of the horse, and later on of the camel as a means of transport, the use of wheeled vehicles, the extension of roads and the increased military efficiency due to the discovery of terrestrial iron. Then followed the profound economic disturbances due to the device of coined money and the change in the nature of debt, proprietorship and trade due to this convenient but dangerous convention. The empires grew in size and range, and men’s ideas grew likewise to correspond with these things. Came the disappearance of local gods, the age of theocrasia, and the teaching of the great world religions. Came also the beginnings of reasoned and recorded history and geography, the first realization by man of his profound ignorance, and the first systematic search for knowledge. For a time the scientific process which began so brilliantly in Greece and Alexandria was interrupted. The raids of the Teutonic barbarians, the westward drive of the Mongolian peoples, convulsive religious reconstruction and great pestilences put enormous strains upon political and social order. When civilization emerged again from this phase of conflict and confusion, slavery was no longer the basis of economic life; and the first paper-mills were preparing a new medium for collective information and co-operation in printed matter. Gradually at this point and that, the search for knowledge, the systematic scientific process, was resumed.