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Every creature becomes the stronger by the opposition it overcomes. Natural Selection gives speed, where speed is the condition of safety, strength where strength is the condition, keenness and quickness of sense-perception where these are demanded. Natural Selection works upon these attributes and tends to perfect them. Any group of men or beasts or birds brought under any unusual strain from cold, hunger, labor, effort, will undergo a weeding-out process. Populate the land with more animal life than it can support, or with more vegetable forms than it can sustain, and a weeding-out process will begin. A fuller measure of vitality, or a certain hardiness and toughness, will enable some species to hold on longer than others, and, maybe, keep up the fight till the struggle lessens and victory is won.

The flame of life is easily blown out in certain forms, and is very tenacious in others. How unequally the power to resist cold, for instance, seems to be distributed among plants and trees, and probably among animals! One spring an unseasonable cold snap in May (mercury 28) killed or withered about one per cent of the leaves on the lilacs, and one tenth of one per cent of the leaves of our crab-apple tree. In the woods around Slabsides I observed that nearly half the plants of Solomon’s-seal (Polygonatum) and false Solomon’s-seal (Smilacina) were withered. The vital power, the power to live, seems stronger in some plants than in others of the same kind. I suppose this law holds throughout animate nature. When a strain of any kind comes, these weaker ones drop out. In reading the stories of Arctic explorers, I see this process going on among their dog-teams: some have greater power of endurance than others. A few are constantly dropping out or falling by the wayside. With an army on a forced march the same thing happens. In the struggle for existence the weak go to the wall. Of course the struggle among animals is at least a toughening process. It seems as if the old Indian legend, that the strength of the foe overcome passes into the victor, were true. But how a new species could arrive as the result of such struggle is past finding out. Variation with all forms of life is more or less constant, but it is around a given mean. Only those acquired characters are transmitted that arise from the needs of the organism.

A vast number of changes in plants and animals are superficial and in no way vital. It is hard to find two leaves of the same tree that will exactly coincide in all their details; but a difference that was in some way a decided advantage would tend to be inherited and passed along. It is said that the rabbits in Australia have developed a longer and stronger nail on the first toe of each front foot, which aids them in climbing over the wire fences. The aye-aye has a specially adapted finger for extracting insects from their hiding-places. Undoubtedly such things are inherited. The snowshoes of the partridge and rabbit are inherited. The needs of the organism influence structure. The spines in the quills in the tails of woodpeckers, and in the brown creeper, are other cases in point. The nuthatch has no spines on its tail, because it can move in all directions, as well with head down as with head up. I have read of a serpent somewhere that feeds upon eggs. As the serpent has no lips or distendable cheeks, and as its mechanism of deglutition acts very slowly, an egg crushed in the mouth would be mostly spilled. So the eggs are swallowed whole; but in the throat they come in contact with sharp tooth-like spines, which are not teeth, but downward projections from the backbone, and which serve to break the shells of the eggs. Radical or vital variations are rare, and we do not witness them any more than we witness the birth of a new species. And that is all there is to Natural Selection. It is a name for a process of elimination which is constantly going on in animate nature all about us. It is in no sense creative, it originates nothing, but clinches and toughens existing forms.