John Fiske perceived that human history has been greatly affected by the fact that man has a longer infancy than the other animals. A creature which grows to its full stature and faculties in a few hours or weeks or months or even years has not the same opportunity to travel far in knowledge or to build its intelligence upon observations and conclusions as has the creature which normally matures through at least a score of years. There still remains to be studied the effect upon mankind of the deliberate prolongation of infancy which, particularly in Europe and America, has been going on for something over a century. Perhaps it should be called less a prolongation of infancy than a discovery that infancy actually lasts longer than had been realized. The social effect is much the same. In the eighteenth century the unproductive and acquisitive period of infancy for boys rarely lasted beyond twenty years, even for those who were trained at the colleges and universities. For the same class in the twentieth century—a class now proportionately larger than then—a period of twenty-five years is nearer the average. The shift is even more marked as regards girls, who a hundred years ago were likely to be married at seventeen or eighteen but who now are quite likely to remain unmarried till twenty-five, and very many, of course, till later. What has become of those years of human life thus lost to adult society, or at least diverted to new purposes? It will not do to answer that such years of youth have been offset by the years added at the end of life through the advance of hygiene and medicine. Even if the total number were the same—and there are no figures to prove or to disprove it—there would still be an incalculable difference in quality. Consider the matter in a simple biological aspect. The postponement of marriage has reduced the number of children born, and has therefore released for other functions a vast amount of human energy once devoted by very young women to gestation and lactation. Anyone who has had occasion to observe a group of girls in the schools and colleges of this generation knows how tremendous is the store of surplus energy for which there is no biological outlet and which too often fails to be sublimated as it might well be into other forms of service. The quantity of such energy which the war showed to be in reserve should not have been a surprise to the teachers or observers of youth. No more should it have been a surprise that those who were thought of as mere boys should have suddenly and successfully taken up heavier labours and larger responsibilities than they had known before. The energy had been all the time in existence, though it had been spent on study or sports or dissipation. Thousands and thousands of years had instructed the race to give about so many years and about so much energy to youth, and the arbitrary customs of a century could not accomplish anything but the most superficial changes.