While such conservatism, in so far as it is judicial, is of value to society, looking at it from the viewpoint of biology we see also some bad features. _Senex_, the old man, often says to younger people, "These things you pursue are valueless--I too have sought them, later abandoned the search and now see my folly;" not realizing that if his blood were to resume its former chemical character he would return to the quest. Elderly people, then, biological neuters, come especially within the problem of the economical use of the social as distinguished from the biological capacities of the race. They affect the sex problem proper, which applies to a younger age-class, only through their opinions. Some of these opinions are hangovers from the time in their own lives when they had stronger sexual interests, and some are peculiar to people of their readjusted glandular activity. Their reproductive contribution to society has been made. Pre-pubertal childhood and youth, on the contrary, has its biological contributions to society still before it. The glandular activity of boys and girls is perhaps not so unlike as to justify society in giving them a different kind of education and preparation for group life. The excuse for two sorts of training is that the two sexes will not do the same work after puberty. Hence the question of youthful training is sociological almost entirely--not biological--or rather, it rests upon the biology, not of childhood but of the reproductive period, which society anticipates. Instead of scattering attention over the whole history of the universe, then, or even over the general field of biology, in dealing with sex as a social problem, the emphasis must be upon the human life cycle during the functional-reproductive period. Other biological data than that which concerns this period is merely introductory or explanatory. The extent to which the sociological problem involved is linked up with general biological considerations like natural selection, adaptation and specialization will be summarized in a separate chapter. Earlier female maturity and puberty, as well as lighter structure, have already been accounted for by the metabolism, especially of the calcium salts. These have also been shown to be the key fact in the monthly periodicity of the mammalian female. Nearly all of the anatomical and physiological sex differences catalogued by such pioneer workers as Ellis, Ploss, Thomas and Bucura are simply what we should expect from the less active and in some ways peculiar metabolism of woman.