All animals have a second fundamental tendency which is no less imperious than that of the preservation of life. All living creatures are irresistibly driven to reproduce themselves. Man is the only animal who can oppose the barrier of his will against the unleashing of his sexual appetite. There have been ascetics in all ages but they have always been few for, after hunger and thirst, the sexual appetite is the most urgent of all. Nature sets almost as much importance on the propagation of life as on its preservation. She strikes those whom she is scheming to join together with a kind of madness. The substances liberated in the blood by the testicles or the ovaries act so powerfully on the brain centers that clarity of judgment is obscured. Sexual desire is the undisputed master of individuals and of nations. The history of peoples, like that of families, frequently depends on the genetic caprices of its rulers. Vast numbers of men have sacrificed fortune or honor in obedience to the impulse of their genital glands. The need to propagate the race can at moments dominate the need to preserve life; love is literally stronger than death. We must not confuse love with genetic desire. Love surpasses desire as much as a conflagration surpasses the flame of a match. It is a product, still somewhat mysterious to us, of the ductless glands, the nerve centers and the mind. It causes one human being to give himself for ever to another human being. It forges an indestructible coupling between male and female; it completes the union of bodies by the union of souls. It assures permanence, peace and happiness in the family; three things which are indispensable to the best development of man's offspring. It constitutes the subtlest and most impressive of the processes employed by nature to ensure the propagation of the race and the raising of the individual to his highest level.

In the handing on of life, the female plays a far more important part than the male. It is in the tissues and in the soul of woman that we can decipher the purposes of the law of the propagation of the race. Females of all species have an almost sacred respect for their young. Mother love goes far deeper than sexual love. The bitch, like the lioness, defends her litter with reckless courage. Woman, when she is not degenerate, does not hesitate to give her life for her children. Unconsciously she follows the law written in her flesh and blood since before the dawn of humanity. Nature prefers the child to the mother. At the outset of the famine in Madrid, the women grew lean, but still bore children of normal weight. But, as the quantity of food had been too little to satisfy the needs of both mother and fetus, the fetus had grown at the mother's expense. So too, the mother's milk hardly varied in quality and quantity. The baby flourished but the nursing mother lost a quarter of her weight during the period of lactation. Thus the mother was automatically sacrificed to the child.

In other circumstances sacrifice, instead of being unconscious, becomes voluntary. Parents usually prefer the well-being of their children to their own. During the famine in Paris many parents and grandparents went without food in favor of the young and sometimes died as the result.

In dogs, maternal love only lasts for a short time; in monkeys it persists much longer. In the human species, it never ceases, for man's progeny need love and their mother needs to love. However long they live, however humble their position, parents who have suceeded in bringing up satisfactory children feel, in their last moments, that they have fully accomplished their destiny. In the sickness or infirmity of old age they are rewarded by the serene joy which nature grants to those who have obeyed her completely.

Men and women are different from each other but complementary. They are particularized by far more than their genital organs and their physical conformation. Their cells, their body fluids and even their blood carry the anatomical or chemical imprint of their sex. It is literally in the very depths of the tissues that the individual's destiny of propagating his species is inscribed. The genetic impulse which appears at puberty comes under the influence of unknown causes, of the mysterious ductless glands.

The pituitary body, this little group of glandular cells which is partly enclosed in the base of the skull, lets loose certain very active substances into the blood. These substances are carried by the blood stream to the testicles or the ovaries and condition their functioning. The suprarenal and thyroid glands also contribute to genital activity. At the moment of puberty they determine the appearance of the specific characteristics of either sex. It is evident that the organism is entirely regulated with reference to the sexual function and hence to the propagation of life. Woman is far more specifically designed for this part than man. Her organic and psychic functions are centered on the cyclic changes of the ovary. Tota mulier in utero, said the ancients. The manufacture of the ovules, the preparation for eventual motherhood, pregnancy and suckling are woman's natural destiny. If she eludes this destiny, danger awaits her. Lack of physical and mental balance is the price woman has to pay when living conditions or her own will prevent her from fulfilling her natural function. Mother love is not a virtue; it is a function of the feminine nervous system as mother's milk is a secretion of the mammary glands. Both depend on the same substance - prolactine, which is set loose in the blood by the posterior lobe of the pituitary body. This gland, through its action on the genital organs, the breasts and the brain, directs both the impulses which lead to copulation and those which give a woman the love for her child and the possibility of suckling it.

The progress of contraceptive methods has dissociated the sexual act from impregnation. At the same time, abortion has ceased to be considered a crime. Both man and woman have left off obeying the law of the propagation of the race. At first nature remained silent. The transgressors themselves were punished lightly or not at all. Then came fearful catastrophes. France has declined, England is following suit and a great qualitative change is taking place in the United States. The severity of the punishment proves how grave was the fault.

Yet even for the moderns, the need to propagate the race remains as fundamental as the need to conserve life. It is rooted in our physical and mental structure; our whole organism is permeated with sexuality. The glands which produce the elements of the future being are also those which give strength and courage to his parent. To propagate life is both a primordial urge and an essential need.