But it is different with man. Man is a being capable of subduing his instincts. A man does not ravish every female that stirs his senses; he does not devour every piece of food that entices him; he does not knock down every fellow he would like to kill. He arranges his wishes and desires into a scale, he chooses; in short, he acts.

Acting man rationalizes the satisfaction of his sexual appetites. Their satisfaction is the outcome of a weighing of pros and cons. Man does not blindly submit to a sexual stimulation like a bull; he refrains from copulation if he deems the costs—the anticipated disadvantages—too high. In this sense we may apply the term moral restraint.

Rationalization of sexual intercourse involves the rationalization of proliferation. Methods of rationalizing the increase of progeny were adopted which were independent of abstention from copulation. People resorted to the egregious and repulsive practices of exposing or killing infants and of abortion. Finally they learned to perform the sexual act in such a way that no pregnancy results.

Social cooperation is impossible if people give rein to the natural impulse of proliferation. In restricting procreation man adjusts himself to the natural conditions of his existence. The rationalization of the sexual passions is an indispensable condition of civilization and societal bonds. Its abandonment would in the long run not increase but decrease the numbers of those surviving, and would render life for everyone as poor and miserable as it was many thousands of years ago for our ancestors.