According to Karl Pearson this “law of the greater variability of the male” was first stated by Darwin. Somewhat earlier, the anatomist Meckel had concluded that the female is more variable than the male. It is interesting to note in passing that he consequently judged “variation a sign of inferiority.” By the time Burdach, Darwin, and others had declared the male more variable, however, variation had become an advantage and the basis and hope of all progress. To-day great social significance is attached to the comparative variability of the sexes, especially in its application to the questions of sex differences in mental achievement. Probably the outstanding English-speaking supporters of the theory in its modern form have been Havelock Ellis and Dr. G. Stanley Hall. But even so cautious a student as Dr. E. L. Thorndike has granted it his guarded support. And Dr. James McKeen Cattell has explained the results of his study of 1000 eminent characters of history by means of it. Indeed many others hold the theory in one form or another--e.g. Münsterburg, Patrick. What is most important, of course, is that its supporters do not stop with the mere statement of the theory. They ascribe to it tremendous effects in the past and ask for it a large influence in the shaping of our policies in the present. For Havelock Ellis, the greater variability of the male “has social and practical consequences of the widest significance. The whole of our human civilization would have been a different thing if in early zoölogical epochs the male had not acquired a greater variational tendency than the female.” (“Man and Woman,” p. 387.) Professor Hall builds up upon it a scheme of gushingly paradisaical (and properly boring) education for the adolescent girl, which “keeps the purely mental back” and develops the soul, the body, and the intuitions. (“The Psychology of Adolescence,” Vol. II, Chap. 17.) Just because Professor Thorndike is so careful in his statements, his practical deductions from the theory are most interesting: “Thus the function of education for women, though not necessarily differentiated by the small differences in average capacity, is differentiated by the difference in range of ability. Not only the probability and desirability of marriage and the training of children as an essential feature of women’s career but also the restriction of women to the mediocre grades of ability and achievement should be reckoned with by our educational systems. The education of women for such professions as administration, statesmanship, philosophy, or scientific research, where a few very gifted individuals are what society requires, is far less needed than education for such professions as nursing, teaching, medicine, or architecture, where the average level is essential. Elementary education is probably an even better investment for the community in the case of girls than in the case of boys; for almost all girls profit