As a primary datum we may note the increasing population of the countries of Europe and North America (Fig. 1). The countries whose population is increasing most rapidly are the United States, Russia, and the German Empire. We know that one important factor of the increase in this country is that of immigration, but this is not sufficient to account for the total. There is continued multiplication of the native population, and of the immigrant after he is here. We wish only to point out in connection with this diagram the steady trend of the population upward, and the fact that obviously somewhere there must be a limit. This cannot go on without end. [Illustration: FIG. 1.--INCREASE OF POPULATION IN THE UNITED STATES AND THE PRINCIPAL COUNTRIES OF EUROPE FROM 1800 TO 1900 (From "Statistical Atlas," Twelfth Census of the United States.)] An extremely pertinent fact here has been disclosed by Pearson and is based upon very extensive observations among several different classes and nations. It is this--that one fourth of the married population of the present generation produce one half of the next generation. The death rate and the ratio of unmarried to married being what they are, this relation may be stated in this way--twelve per cent of all the individuals born in the last generation produced one half of the present generation. "This is not only a general law, but it is practically true for each class in the community." This conclusion is based upon data from the English, Danish, and Welsh peoples of professional, domestic, commercial, industrial, and pastoral classes, and the per cent of married persons found to be producing one half of each generation varies from twenty-three to twenty-seven with an average of twenty-five per cent. We must ask at once--what is the source of this fourth which is contributing double its quota to the next generation? Is this twenty-five per cent drawn proportionately from all classes of society or are some groups contributing relatively more than others? Is there any relation between this superfertility and the possession of desirable or undesirable characteristics? We may answer at once--there is a distinct and positive relation between civic undesirability and high fertility. We shall return to this subject at the close of the next chapter; only the bare fact is to be mentioned at this time. It is a matter of common notice and remark that to-day, in England at any rate, there is a dearth of youthful ability. It exists in commerce, science, literature, politics, the bar, the church. We cannot dismiss as merely fashionable the statements that the able classes are not replacing themselves, that men of ability are less able than formerly. Whether or not this is also the condition in America to-day, we know that it soon will be the condition unless steps are taken to bring about a positive relation between civic desirability and ability and the numerical production of offspring.