The theory of evolution has taught us in science to think in larger terms of time, so that we no longer raise the question whether European colonists in Africa can turn into negroes, though we do find the recent amazing statement that the Yankee, in his tall, gaunt figure, "the colour of his skin, and the formation of his hair, has begun to differentiate himself from his European kinsman and approach the type of the aboriginal Indians."[28] Evolution tells the story of modification by a succession of infinitesimal changes, and emphasizes the permanence of a modification once produced long after the causes for it cease to act. The mesas of Arizona, the earth sculpture of the Grand Canyon remain as monuments to the erosive forces which produced them. So a habitat leaves upon man no ephemeral impress; it affects him in one way at a low stage of his development, and differently at a later or higher stage, because the man himself and his relation to his environment have been modified in the earlier period; but traces of that earlier adaptation survive in his maturer life. Hence man's relation to his environment must be looked at through the perspective of historical development. It would be impossible to explain the history and national character of the contemporary English solely by their twentieth century response to their environment, because with insular conservatism they carry and cherish vestiges of times when their islands represented different geographic relations from those of to-day. Witness the wool-sack of the lord chancellor. We cannot understand the location of modern Athens, Rome or Berlin from the present day relations of urban populations to their environment, because the original choice of these sites was dictated by far different considerations from those ruling to-day. In the history of these cities a whole succession of geographic factors have in turn been active, each leaving its impress of which the cities become, as it were, repositories. [Sidenote: Effect of a previous habitat.]