species thus becomes in the main the work of the parental instinct. In such species the protection and cherishing of the young is the constant and all-absorbing occupation of the mother, to which she devotes all her energies, and in the course of which she will at any time undergo privation, pain, and death. The instinct becomes more powerful than any other, and can override any other, even fear itself; for it works directly in the service of the species, while the other instincts work primarily in the service of the individual life, for which Nature cares little.... When we follow up the evolution of this instinct to the highest animal level, we find among the apes the most remarkable examples of its operation. Thus in one species the mother is said to carry her young one clasped in one arm uninterruptedly for several months, never letting go of it in all her wanderings. This instinct is no less strong in many human mothers, in whom, of course, it becomes more or less intellectualized and organized as the most essential constituent of the sentiment of parental love. Like other species, the human species is dependent upon this instinct for its continual existence and welfare. It is true that reason, working in the service of the egotistic impulses and sentiments, often circumvents the ends of this instinct and sets up habits which are incompatible with it. But when that occurs on a large scale in any society, that society is doomed to rapid decay. But the instinct itself can never die out save with the disappearance of the human species itself; it is kept strong and effective just because those families and races and nations in which it weakens become rapidly supplanted by those in which it is strong. "It is impossible to believe that the operation of this, the most powerful of the instincts, is not accompanied by a strong and definite emotion; one may see the emotion expressed unmistakably by almost any mother among the higher animals, especially the birds and the mammals--by the cat, for example, and by most of the domestic animals; and it is impossible to doubt that this emotion has in all cases the peculiar quality of the tender emotion provoked in the human parent by the spectacle of her helpless offspring. This primary emotion has been very generally ignored by the philosophers and psychologists; that is, perhaps, to be explained by the fact that this instinct and its emotion are in the main decidedly weaker in men than women, and in some men, perhaps, altogether lacking. We may even surmise that the philosophers as a class are men among whom this defect of native endowment is relatively common."