But it would be a very great mistake to suppose that the lapse in the material civilisation which undoubtedly took place in the later day of imperial Rome coincided with an entire change in the social conditions of the people. No trait in human nature is more fixed and more insistent than the tendency to cling to the ways of our forbears. Conservatism is the dominant motive of the mass of humanity. What our fathers thought and believed, we for the most part think and believe. The average man inherits his religion and his politics much as he inherits the colour of his eyes; and has scarcely more likelihood of changing one than the other. In the sweep of the centuries, ideas and customs do change, to be sure; but the changes, in so far as they pertain to long-standing principles or customs, are always slow and gradual. Geologists of the nineteenth century demonstrated, after long study and much argument, that there are no cataclysmic vaults in the sweep of the geological and biological ages. The lesson thus taught regarding nature at large is one which the sociologist might apply to his own would-be science with advantage. In particular this lesson should be called to the attention of the student of history who would have us believe that there was a sudden and catastrophic change in the mentality of the people of Italy in the fifth century A.D. No one who appreciates the true character of human progress will be disposed to believe, in the absence of confirmatory evidence, that the Italian of the sixth century differed very greatly in his desires and aspirations from his grandparent who lived while Rome was yet nominally governed by an Italian emperor. The successive hordes of barbarians that swept down from the north took booty wherever they could find it, and impoverished the country, but for the most part they were not imbued with the spirit of wanton destruction. We may well believe that they looked rather with awestruck admiration akin to reverence upon the wonderful monuments of a civilisation so different from anything they had previously witnessed. We know that relatively civilised nations of the north sacked Rome in the sixteenth century more disastrously than it was sacked by their alleged barbaric precursors of the earlier millennium. Moreover, these invaders from the north were not omnipresent. They came and went at relatively long intervals, and there were some territories that they did not greatly molest. And the history of invasions everywhere goes to show that after the moment of initial conquest the barbaric vanquisher becomes, in matters of custom and thought, a follower rather than a leader of the vanquished.