This unity of character is very largely due to continuous descent from a common cultural ancestor. The civilization of the West is fundamentally one not because the peoples of the West are one racially. They are not so. They comprise every branch of the Aryan family and a considerable admixture of quite other stocks. Their civilization owes its common characteristics mainly to a common origin and continued interaction. That is why it is in the mass a community of ideas, for ideas pass from man to man and from nation to nation more readily than institutions, more readily far than character, more readily perhaps than anything except material goods. In the realm of ideas Western civilization forms a single commonwealth of informal but of exceeding democratic constitution. This freedom, indeed, it owes in large measure to its international character, for there are constantly arising local and temporary dictators, arbiters of fashion in the ideas of politics, philosophy, and even of science. Within a narrow circle such a dictator often has it all his own way, but it is seldom that he can maintain a prolonged ascendancy throughout the international commonwealth unless there is some pretty solid foundation for his doctrine. This commonwealth has its foundations in the past. It derives in the first instance from the unity of mediaeval Christendom, where it enjoyed the advantage of a common language of learning, the gradual loss of which is imperfectly compensated by the possession of two or three modern languages alone by the educated man of the present day. Through mediaeval Christendom and through the Arabic schools, which can hardly be regarded as a part of Western civilization but in the Middle Ages were rather its teachers, it derives from the Greco-Roman world, and through the Greco-Roman world from the Greeks themselves. The Greeks in their turn were aware that they owed the rudiments of their science to the ancient civilizations of the Nile and the Euphrates. Thus in the intellectual world there is a continuity stretching back six thousand years or more to the beginnings of recorded civilization. More than once the continuity is nearly broken, but some strand is always preserved, and it is in this continuity in the world of ideas that we get the main evidence of such progress as human history reveals.