CHAPTER X

PRESENT ASPECTS OF THE THEORY OF EVOLUTION

In all our study we have taken for granted the truth of the theory of evolution. If you are not already persuaded of this by the writings of Darwin, Wallace, and many others, no words or arguments of mine would convince you. We have used as the foundation of our argument only the fundamental propositions of Mr. Darwin's theory.

But while all evolutionists accept these propositions they differ more or less in the weight or efficiency which they assign to each. In a sum in multiplication you may gain the same product by using different factors; but if the product is to be constant, if you halve one factor, you must double another. Evolution is a product of many factors. One evolutionist lays more, another less, emphasis on natural selection, according as he assigns less or more efficiency to other forces or processes. Furthermore, evolutionists differ widely in questions of detail, and some of these subsidiary questions are of great practical importance and interest. It may be useful, therefore, to review these propositions in the light of the facts which we have gathered, and to see how they are interpreted, and what emphasis is laid on each by different thinkers.

The fundamental fact on which Mr. Darwin's theory rests is the "struggle for existence." Life is not

something to be idly enjoyed, but a prize to be won; the world is not a play-ground, but an arena. And the severity of the struggle can scarcely be overrated. Only one or two of a host of runners reach the goal, the others die along the course. Concerning this there can be no doubt, and there is little room for difference of interpretation.

The struggle may take the form of a literal battle between two individuals, or of the individual with inclemency of climate or other destructive agents. More usually it is a competition, no more noticeable and no less real than that between merchants or manufacturers in the same line of trade.

The weeds in our gardens compete with the flowers for food, light, and place, and crowd them out unless prevented by man. And when the weeds alone remain, they crowd on each other until only a few of the hardiest and most vigorous survive. And flowers, by their nectar, color, and odor, compete for the visits of insects, which insure cross-fertilization. And fruits are frequently or usually the inducements by which plants compete for the aid of animals in the dissemination of their seeds. So there is everywhere competition and struggle; many fail and perish, few succeed and survive.

In a foot-race it is often very difficult to name the winner. Muscle alone does not win, not even good heart and lungs. Good judgment, patience, coolness, courage, many mental and moral qualities, are essential to the successful athlete. So in the struggle for life. The race is not always to the swift, nor the battle to the strong.

The total of "points" which wins this "grand

prize" is the aggregate of many items, some of which appear to us very insignificant. Hence, when we ask, "Who will survive?" the answer is necessarily vague. Mr. Darwin's answer is, Those best conformed to their environment; and Mr. Spencer's statement of the survival of the fittest means the same thing.

The judges who pronounce and execute the verdict of death, or award the prize of life, are the forces and conditions of environment. We have already considered the meaning of this word. Many of its forces and conditions are still unknown, or but very imperfectly understood. But known or unknown, visible or invisible, the result of their united action is the extinction or degradation of these individuals which deviate from certain fairly well-marked lines of development. We must keep clearly before our minds the fact that the world of living beings makes up by far the most important part of the environment of any individual plant or animal. Two plants may be equally well suited to the soil and climate of any region; but if one have a scanty development of root or leaf, or is for any reason more liable to attacks from insects or germs, other things being equal, it will in time be crowded out by its competitor. Worms are eaten by lower vertebrates, and these by higher. An animal's environment, like that of a merchant or manufacturer, is very largely a matter of the ability and methods of its competitors. And man, compelled to live in society, makes that part of the environment by which he is most largely moulded.

This process of extinction Mr. Darwin has called natural selection." Natural selection is not a force but a process, resulting from the combined action of

the forces of environment. It is not a cause in any proper sense of the word, but a result of a myriad of interacting forces. The combination of these forces in a process of natural selection leading directly to a moral and spiritual goal demands an explanation in some ultimate cause. This explanation we have already tried to find.

It is a process of extinction. It favors the fittest, but only by leaving them to enjoy the food and place formerly claimed, or still furnished, by the less fit. In any advancing group, as the less fit are crowded out, and the better fitted gain more place and food and more rapid increase, the whole species becomes on an average better conformed. More abundant nourishment and increased vigor seem also to be accompanied by increased variation. And by the extinction of the less fit the probability is increased that more fit individuals will pair with one another and give rise to even fitter offspring, possessing perhaps new and still more valuable variations.

But if, of a group of weaker forms, those alone survive which adopt a parasitic life, those which in adult life move the least will survive and reproduce; there will result the survival of the least muscular and nervous. This degeneration will continue until the species has sunken into equilibrium, so to speak, with its surroundings. Here natural selection works for degeneration. Sessile animals have had a similar history. But these parasitic and sessile forms had already been hopelessly distanced in the race for life. Their presence cannot impede the leaders; indeed their survival is necessary to directly or indirectly furnish food for the better conformed. In the animal

and plant world there is abundant room and advantage at the top.

Once more, natural selection works as a rule for the survival of individuals, only indirectly for that of organs composing, or of species including, these individuals. It may work for the development of a trait or structure which, while of no immediate advantage to the individual, increases the probability of its rearing a larger number of fitter offspring. Thus defence of the young by birds may be a disadvantage to the parent, but this is more than counterbalanced in the life of the species by the number of young coming to maturity and inheriting the trait. Even here natural selection favors the survival of the trait indirectly by sparing the descendants of the individual possessing it. Natural selection may always work on and through individuals without always working for their sole and selfish advantage.

In human society we find the selection of families, societies, nations, and civilizations going on, but mainly as the result of the survival of the fittest individuals.

There may very probably be a struggle for existence between organs or cells in the body of each individual. The amount of nutriment in the body is a more or less fixed quantity; and if one organ seizes more than its fair share, others may or must diminish for lack. But the limit to this usurpation must apparently be set by the crowding out of those individuals in which it is carried too far. Natural selection, so to speak, leaves the individual responsible for the distribution of the nutriment among the organs, and spares or destroys the individual as this usurpation proves for its advantage or disadvantage.