The greatest good which may come from the sex-education movement is not prevention or elimination of social diseases, it is not improved health, it is not general acceptance of the moral law of sex, it is not one or all these that are devoutly to be hoped for; but far greater than such possible results from sex-education, it will bring to many a man and woman a deeper, nobler, and purer knowledge of what sex means for the coming race and of what it means now to each individual who realizes life's fullest possibilities in conjugal affection which culminates in new life and new motives for more affection. Such an understanding of sex in relation to home life will help this old world more than anything else which sex-education may accomplish. [Sidenote: The greatest sex problem.] The problems of sex and marriage deserve far more attention than can be given in this lecture. I am convinced that knowledge of sex in its physical, psychical, social, and aesthetic aspects is the only sure foundation for harmonious marriage under modern conditions. Therefore, I believe this to be the greatest sex problem open to educational attack. Sec. 13. _The Eighth Problem for Sex-instruction: Eugenics_ [Sidenote: Meaning of eugenics.] Eugenics, or the science of human good breeding, is just now the most popular of the problems concerning human sex and reproduction. In recent years, the biological investigators of heredity have published some startling facts which show that the human race must soon check its reckless propagation of the unfit and encourage reproduction by the best types of men and women. This is not the place for a review of the eugenic propositions. Those interested will find them in non-technical form in many books (see the bibliographical chapter of this book, page 248). [Sidenote: Eugenics in biology.] Some of the chief facts of eugenics should be a part of every well-organized scheme of sex-instruction, and taught through biology (Sec. 17). Probably no other topic in biology is so likely to make an ethical-social appeal, for the central point of eugenics is the responsibility of the individual whose uncontrolled sexual actions may transmit undesirable and heritable qualities and bring a train of disaster to generations of descendants. [Sidenote: Relation of eugenics and sex-hygiene.] At this point we digress to correct the widespread error in confusing sex-hygiene and eugenics. Many people who ought to know better use the two terms synonymously, perhaps because they are afraid of that comparatively novel but frank prefix in "sex-hygiene." The fact is that eugenics and sex-hygiene have little in common. Eugenics is the science of reproducing better humans by applying the established laws of genetics or heredity. In brief, it means, on the positive side, selecting desirable people as parents; and, negatively, preventing propagation by the undesirables. This is the sum total of the task of eugenics in the accurate sense of the term.