"Marrying a man to reform him" is a speculation in which many women have indulged and usually--it may be said without fear of contradiction--with unfortunate results. It is always likely that she will fail to reform him; it is certain that she can not reform his germ-plasm. Psychologists agree that the character of a man or woman undergoes little radical change after the age of 25; and the eugenist knows that it is largely determined, _potentially_, when the individual is born. It is, therefore, in most cases the height of folly to select a partner with any marked undesirable trait, with the idea that it will change after a few years. All these suggestions have in general been directed at the young man or woman, but it is admitted that if they reach their target at all, it is likely to be by an indirect route. No rules or devices can take the place, in influencing sexual selection, of that lofty and rational ideal of marriage which must be brought about by the uplifting of public opinion. It is difficult to bring under the control of reason a subject that has so long been left to caprice and impulse; yet much can unquestionably be done, in an age of growing social responsibility, to put marriage in a truer perspective. Much is already being done, but not in every case of change is the future biological welfare of the race sufficiently borne in mind. The interests of the individual are too often regarded to the exclusion of posterity. The eugenist would not sacrifice the individual, but he would add the welfare of posterity to that of the individual, when the standards of sexual selection are being fixed. It is only necessary to make the young person remember that he will marry, not merely an individual, but a family; and that not only his own happiness but to some extent the quality of future generations is being determined by his choice. We must have (1) the proper ideals of mating but (2) these ideals must be realized. It is known that many young people have the highest kind of ideals of sexual selection, and find themselves quite unable to act on them. The college woman may have a definite idea of the kind of husband she wants; but if he never seeks her, she often dies celibate. The young man of science may have an ideal bride in his mind, but if he never finds her, he may finally marry his landlady's daughter. Opportunity for sexual selection must be given, as well as suitable standards; and while education is perhaps improving the standards each year, it is to be feared that modern social conditions, especially in the large cities, tend steadily to decrease the opportunity. Statistical evidence, as well as common observation, indicates that the upper classes have a much wider range of choice in marriage than the lower classes. The figures given by Karl Pearson for the degree of resemblance between husband and wife with regard to phthisis are so remarkable as to be worth quoting in this connection: