The ever-present instinct of fear in all wild creatures and in children, and the quickness with which it can be aroused in all persons, throw light upon the crueler aspects of this struggle for existence which is common to all forms of animal life. Had life never been beset with perils, we should have been strangers to the emotion of fear, as would all other creatures. Even the fly that alights on my paper as I write fears my hand. It is ever on guard against its natural enemies. This is the proof of the universal struggle. Among the lower forms the struggle or competition of the fleet with the slow, the cunning with the stupid, the sharp-eyed, the sharp-eared, and the keen of scent with those less so; of the miscellaneous feeders with the more specialized feeders; and, among mankind, the competition of men of purpose, of foresight, of judgment, of experience, of probity, and of other personal resources, with men who are deficient in these things; and, among nations and peoples, the inevitable competition of those who cherish the highest national ideals, the best-organized governments, the best race inheritance, the most natural resources, and so on, with the less fortunate in these respects--all this struggle and competition, I say, is beneficent and on the road to progress. Myriads of different types of animal and vegetable life fit into the scheme of organic nature without conflict or hindrance, but when there is conflict, the strong prevail. The small and the gigantic, the feeble and the mighty, the timid and the bold, the frail and the robust--birds, insects, mice, squirrels, cattle--exist in the same landscape and all prosper. Only when there is rivalry do the feeble go to the wall, which means only that their numbers are kept down. The cats do not exterminate the mice and rats, nor do the hawks and owls exterminate the other birds; they are a natural check on their undue increase. Nature’s checks and balances are all important. When species subsist upon species, as weasels upon rodents and hawks upon other birds, there seems to be some law that keeps the bloodthirsty in check. Why should there be so few weasels, since they appear as prolific as their victims? Why so few pigeon hawks, since the hawks have no natural enemies, while the trees swarm with finches and robins?