Vaerting found that the fathers who were themselves not notably intellectual have a decidedly more prolonged power of procreating distinguished children than is possessed by distinguished fathers. The former may become the fathers of eminent children from the period of sexual maturity up to the age of forty-three or beyond. When, however, the father is himself of high intellectual distinction, the records show that he was nearly always under thirty, and usually under twenty-five years of age at the time of the birth of his distinguished son, although the proportion of youthful fathers in the general population is relatively small. The eleven youngest fathers on Vaerting's list, from twenty-one to twenty-five years of age, were with one exception themselves more or less distinguished; while the fifteen oldest, from thirty-nine to sixty years of age, were all without exception undistinguished. Among the sons on the latter list are to be found much greater names (such as Goethe, Bach, Kant, Bismarck, Wagner, etc.) than are to be found among the sons of young and more distinguished fathers, for here is only one name (Frederick the Great) of the same caliber. The elderly fathers belonged to the large cities, and were mostly married to wives very much younger than themselves. Vaerting notes that the most eminent men have frequently been the sons of fathers who were not engaged in intellectual avocations at all, but earned their living as humble craftsmen. He draws the conclusion from these data that strenuous intellectual energy is much more unfavorable than hard physical labor to the production of marked ability in the offspring. Intellectual workers, therefore, he argues, must have their children when young, and we must so modify our social ideals and economic conditions as to render this possible. Vaerting, however, holds that the mother need not be equally young; he finds some superiority, indeed, provided the father is young, in somewhat elderly mothers, and there were no mothers under twenty-three on the list. The rarity of genius among the offspring of distinguished parents he attributes to the unfortunate tendency to marry too late; and he finds that the distinguished men who marry late rarely have any children at all. Speaking generally, and apart from the production of genius, he holds that women have children too early, before their psychic development is completed, while men have children too late, when they have already "in the years of their highest psychic generative fitness planted their most precious seed in the mud of the street."