"Mr. J. Mathews Duncan, in his work on Fecundity, Fertility, Sterility and allied topics, has given results of statistics which show that mothers of twenty-five bear the finest infants, and that from mothers whose ages at marriage range from twenty to twenty-five years there come infants which have a lower rate of mortality than those resulting from marriages consummated when the mothers' ages are smaller or greater. The apparent slight incongruity between these two statements being due to the fact that whereas marriages commenced before twenty and twenty-five cover the whole of the period of highest vigor, marriages commenced at five and twenty cover a period which lacks the years during which vigor is rising to its climax and includes only the years of decline from the climax." This quotation from Mr. Spencer needs a qualifying remark. Mr. Galton, in his work on Hereditary Genius, found that the average age of mothers of men of the greatest ability was about thirty, and of their fathers thirty-five. In such cases, the physical and intellectual strength must have been above the average, and, consequently, it continued to a more advanced age. Besides, those of great ability mature later. It may also be added that Duncan's statistics, quoted by Spencer, are average statistics gathered from tables of mortality, and include every class of persons. Now, average statistics do not apply to individual cases, and they would not apply to those highly endowed physically and intellectually. Further, those who are well endowed at birth and whose lives are in accordance with hygienic law, that is, those who do not squander their physiological resources by sensuality, by intemperance, or by excesses of any sort retain their health to a greater age than those whose lives are the reverse. Such are of a youthful physiological age, which is not altogether determined by the actual number of years they have lived, but by very high physiological conditions. From all this we conclude that a very important rule in the production of offspring, if we would have those offspring superior, is to maintain a high degree of health--a condition in which there is a surplus of physiological capital to produce children with endowments equal to, if not superior to, their parents.