Particularly pernicious in tending to prevent marriage is the influence of certain professional schools, some of which have come to require a college degree for entrance. In such a case the aspiring physician, for example, can hardly hope to obtain a license to practice until he has reached the age of 27 since 4 years are required in Medical College and 1 year in a hospital. His marriage must in almost every case be postponed until a number of years after that of the young men of his own class who have followed business careers. This brief survey is enough to prove that the best educated young women (and to a less extent young men) of the United States, who for many reasons may be considered superior, are in many cases avoiding marriage altogether, and in other cases postponing it longer than is desirable. The women in the separate colleges of the East have the worst record in this respect, but that of the women graduates of some of the coeducational schools leaves much to be desired. It is difficult to separate the causes which result in a postponement of marriage, from those that result in a total avoidance of marriage. To a large extent the causes are the same, and the result differs only in degree. The effect of absolute celibacy of superior people, from a eugenic point of view, is of course obvious to all, but the racial effect of postponement of marriage, even for a few years, is not always so clearly realized. The diagram in Fig. 36 may give a clearer appreciation of this situation. Francis Galton clearly perceived the importance of this point, and attempted in several ways to arrive at a just idea of it. One of the most striking of his investigations is based on Dr. Duncan's statistics from a maternity hospital. Dividing the mothers into five-year groups, according to their age, and stating the median age of the group for the sake of simplicity, instead of giving the limits, he arrived at the following table: _Age of mother at_ _Approximate average_ _her marriage_ _fertility_ 17 9.00--6 x 1.5 22 7.50--5 x 1.5 27 6.00--4 x 1.5 32 4.50--3 x 1.5 which shows that the relative fertility of mothers married at the ages of 17, 22, 27 and 32, respectively, is as 6, 5, 4, and 3 approximately. "The increase in population by a habit of early marriages," he adds, "is further augmented by the greater rapidity with which the generations follow each other. By the joint effect of these two causes, a large effect is in time produced."