That the victory does not always fall to the human contestant is tragically demonstrated by the effects of the incessant assaults upon man made by just one kind of living enemy,—the bacillus of tuberculosis. Every year more than one hundred and twenty-five thousand people of the United States die because they are unable to withstand its persistent attacks; five million Americans now living are doomed to death at the hands of these executioners, and the figures must be more than doubled to cover the casualties on the human side in the battles with the regiments of all the species of bacteria causing disease.
The competition between and among the individuals of one and the same species is the third part of the struggle for existence, and it is often unsurpassed in its ferocity. When two lion cubs of the same litter begin to shift for themselves, they must naturally compete in the same territory, and their contest is keener than that which involves either of them and a young lion born ten or fifteen miles away. The seeds of one parent plant falling in a restricted area will be engaged in a competitive struggle for existence that is much more intense than many other parts of nature's warfare. In brief, the intensity of the competition will be directly proportional to the similarity of two organisms in constitution and situation, and to the consequent similarity of vital welfare. The interests of the white man and the Indian ran counter to each other a few hundred years ago, and the more powerful colonists won. The assumption of the white man's burden too often demonstrates the natural effect of diversity of interest, and the domination of the stronger over the weaker. In any civilized community the manufacturer, farmer, financier, lawyer, and doctor must struggle to maintain themselves under the conditions of their total inorganic and social environments; and in so far as the object of each is to make a living for himself, they are competitors. But the contest becomes more absorbing when it involves broker and broker, lawyer and lawyer, financier and magnate, because in each case the contestants are striving for an identical need of success.
Although the severity of the conflict imposed by nature is somewhat modified in the case of social organisms, where community competes with community and nation with nation, no form of social organization has yet been developed where the individual contest carried on by the members of one community has been done away with. It is an inexorable law of nature that all living things must fight daily and hourly for their very lives, because so many are brought into the world with each new generation that there is not sufficient room for all. No organism can escape the struggle for existence except by an unconditional surrender that results in death. Everywhere we turn to examine the happenings of organic life we can find nothing but a wearisome warfare in which it is the ultimate and cruel lot of every contestant to admit defeat.
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What now are the results of variation, over-multiplication, and competition? Since some must die because nature cannot support all that she produces, since only a small proportion of those that enter upon life can find a foothold or successfully meet the hordes of their enemies, which will be the ones to survive? Surely those that have even the slightest advantage over their fellows will live when their companions perish. It is impossible that the result could be otherwise; it must follow inevitably from what has been described before. The whole process has its positive and its negative aspects: the survival of the fittest and the elimination of the unfit. Perhaps it would be more correct to say the more real element is the negative one, for those which are least capable of meeting their living foes and the decimating conditions of inorganic nature are the first to die, while the others will be able to prolong the struggle for a longer or shorter period before they too succumb. Thus the destruction of the unfit leaves the field to the better adapted, that is, to those that vary in such a way as to be completely or at least partially adapted to carry on an efficient life. In this way Darwinism explains the universal condition of organic adjustment, showing that it exists because there is no place in nature for the incompetent.
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Finally we come to the process of inheritance as viewed by Darwin, and its part in the production and perfection of new species. In every case, Darwin said, the efficiency or inefficiency of an animal depends upon its characteristics of an inherited or congenital nature. Variations in these qualities provide the array of more or less different individuals from which impersonal nature selects the better by throwing out first the inferior ones. An organism can certainly change in direct response to environmental influence or by the indirect results of use and disuse, but not unless it is so constituted by heredity as to be able to change adaptively. Therefore the final basis of success in life must be sought in the inherited constitutions of organic forms.
For the reason that the qualities which preserve an animal's existence are already congenital, they are already transmissible, as Darwin contended. Since his time much has been learned about the course of inheritance and its physical basis, and the new discoveries have confirmed the essential truth of Darwin's statement that the congenital characters only possess a real power in the evolution of species.
We must devote some time to the subject of inheritance at a later juncture, but before leaving the matter an additional point must be established here; the selective process deals immediately with congenital results, as the heritable characters that make for success or failure in life, but by doing this it really selects the group of congenital factors behind and antecedent to their effects. For example, an ape that survives because of its superior cunning, does so because it varies congenitally in an improved direction; and the factors that have made it superior are indirectly but no less certainly preserved through the survival of their results in the way of efficiency. Hereditary strains are thus the ultimate things selected through the organic constitutions that they determine and produce.
Natural selection, as the whole of this intricate process, is simply trial and error on a gigantic scale. Nature is such that thousands of varying individuals are produced in order that a mere handful or only one survivor may be chosen to bear the burden of carrying on the species for another generation. The effect of nature's process is judicial, as it were. We may liken the many and varied conditions of life to as many jurymen, before which every living thing must appear for judgment as to its fitness or lack of it. A unanimous verdict of complete or partial approval must be rendered, or an animal dies, for the failure to meet a single vital condition results in sure destruction. Of course, we cannot regard selection as involving anything like a primitive conscious choice. It is because we individualize all of the complex totality of the world as "Nature" with a capital N that so many people unconsciously come to think of it as a human-like personality. He who would go further and hold that all of nature is actually conscious and the dwelling-place of the supernatural ultimate, must beware of the logical results of such a view. What must we think of the ethical status of such a conscious power who causes countless millions of creatures to come into the world and ruthlessly compels them to battle with one another until a cruel and tragic death ends their existence?