The third and culminating cause was the career of military aggression pursued by Charles V; this completed the extermination of the aristocracy of ability and finally plunged Spain into an intellectual torpor which has persisted ever since and from which she can only be raised up by a succession of men of first-rate intellect and character: men such as she seems incapable of producing, because her people has thus been drained of all its most valuable elements, because her eugenic stocks have been exterminated. The fall of Spain illustrates not only the operation of internal social selection affecting certain mental qualities; it illustrates also once more, even more clearly than the fall of Greece, the fact that the civilisation of a people and its power and position in the world depend altogether upon its intellectual aristocracy, and that the fall of a people from a high place necessarily follows the failure to continue to produce such an aristocracy. In the civilised nations of the modern world, the most important kind of selection at work at the present time is what is distinguished as ‘economic selection’ working in conjunction with the formation of the social classes. It has no doubt operated at various times among other civilised peoples, but never so strongly and universally as at present. All the leading civilised nations have passed, in the eighteenth and earlier part of the nineteenth centuries, through a period in which the discoveries of science have enormously increased the productive powers of man and man’s control over, and power of resistance to, the forces of nature. The result has been that everywhere civilised populations have multiplied at a great rate, in a way that has never before occurred. But now this period seems to have definitely come to an end, and to have been succeeded by a new period characterised by three features which threaten to exert a most deleterious effect upon the innate mental qualities of peoples. (1) The world is becoming filled up; the untouched wealth of enormous territories no longer lies open to the grasp of the bold and enterprising. The coloured races are entering into the economic competition in the way foreshadowed by the late C. H. Pearson[132]. The high organisation of every form of economic activity renders the competition for wealth everywhere extremely severe. And at the same time men have come to regard as necessities of life what, but a few generations ago, were the luxuries of the wealthy or unknown even to them; that is to say, the standard of comfort has risen greatly. The combined result of these changes is the increased difficulty of maintaining a family in the upper strata of society.