But the most far-reaching of the forces at work in the family has been the parental instinct and affection with its consequences upon both parents and children. It contributes probably more than any other naturally selected agency to the development of the race in sympathy; it shares with work in the development of responsibility. It is indeed one of the great incentives to industry throughout the higher species of animals as well as in human life. The value of parental care in the struggle for existence is impressively presented by Sutherland.[21] Whereas the fishes which exercise no care for their eggs preserve their species only by producing these in enormous numbers, certain species which care for them maintain their existence by producing relatively few. Many species produce hundreds of thousands or even millions of eggs. The stickleback, which constructs a nest and guards the young for a few days, is one of the most numerous of fishes, but it lays only from twenty to ninety eggs. Birds and mammals with increased parental care produce few young. Not only is parental care a valuable asset, it is an absolute necessity for the production of the higher species. "In the fierce competition of the animated forms of earth, the loftier type, with its prolonged nervous growth, and consequently augmented period of helplessness, can never arise but with concomitant increases of parental care." Only as the emotional tendency has kept pace with the nerve development has the human race been possible. The very refinements in the organism which make the adult a victor would render the infant a victim if it were without an abundance of loving assistance.[22] Whether, as has been supposed by some, the parental care has also been the most effective force in keeping the parents together through a lengthened infancy, or whether other factors have been more effective in this particular, there is no need to enlarge upon the wide-reaching moral values of parental affection. It is the atmosphere in which the child begins his experience. So far as any environment can affect him, this is a constant influence for sympathy and kindness. And upon the parents themselves its transforming power, in making life serious, in overcoming selfishness, in projecting thought and hope on into the future, cannot be measured. The moral order and progress of the world might conceivably spare some of the agencies which man has devised; it could not spare this. § 5. MORAL INTERPRETATION OF THIS FIRST LEVEL