Too often, however, the men of parts follow the example of the brilliant professor who married a "social butterfly." "Why in the world did you do it?" asked an old friend. "Oh, well," answered the professor, "I felt that I had brains enough for both." True, professor, but according to the Mendelian law of heredity, those brains of yours will be halved in each of your children, and quartered in each of your grandchildren. Why should not the future be at least as brilliant as your own generation? Human marriage is ordinarily a hit or miss affair. Men and women, inspired by the loftiest motives, and animated in most matters by supreme good sense, not infrequently grope blindly toward matrimony; often marry uncongenially; and finally bring disgrace upon their own heads, and misery upon their families. Stevenson, with such marriages in mind, writes to the average prospective bridegroom-- "What! you have had one life to manage, and have failed so strangely, and now can see nothing wiser than to conjoin with it the management of some one else's? Because you have been unfaithful in a very little, you propose yourself to be a ruler over ten cities. You are no longer content to be your own enemy; you must be your wife's also. God made you, but you marry yourself; no one is responsible but you. You have eternally missed your way in life, with consequences that you still deplore, and yet you masterfully seize your wife's hand, and blindfold, drag her after you to ruin. And it is your wife, you observe, whom you select. She, whose happiness you most desire, you choose to be your victim. You would earnestly warn her from a tottering bridge or bad investment. If she were to marry some one else, how you would tremble for her fate! If she were only your sister and you thought half as much of her, how doubtfully would you entrust her future to a man no better than yourself!"[18] Here, then, lies the path of eugenic activity for the individual--clear, straight, unmistakable. In the first place, he must never transmit to the future any defect. If he has a transmissible defect, he must have no offspring. This seems but reasonable--an obligation to bring no unnecessary misery into a world where so much already exists. But the individual--free to choose--must go one step further, and in his selection, must seek a mate with the qualities which are complementary to his own.