LAWS OF EVOLUTION.

Let us now examine some of the laws of evolution, as also some of the connecting links which blend one stage of man's development with another, which at first thought would seem unexplainable.

Haeckel[31] summarizes the inductive evidences of Darwinism as follows: 1. Paleontological series (phylogeny); 2. Embryological development of the individual (ontogeny); 3. The correspondence in the terms of these two series; 4. Comparative anatomy (typical forms and structures); 5. Correspondence between comparative anatomy and ontogeny; 6. Rudimentary organs (dipeliology); 7. The natural system of organisms (classification); 8. Geographical distribution (chorology); 9. Adaptation to the environment (œcology); 10. The unity of biological phenomena.

It will of course be impossible to consider even hastily all of the inductive evidence belonging to the several groups mentioned above, for the scope of this work would not permit of it. Only such facts as present themselves most forcibly to the mind will be considered.

Darwinism, as has already been stated, is not the doctrine of evolution; it is, however, a successful attempt to explain the law or manner of evolution. The law of natural selection, pointed out by Darwin, is called by Herbert Spencer, The struggle for existence. Darwin discovered that natural selection produces fitness between organisms and their circumstances, which explains the law of the survival of the fittest.

It is a well-known fact that man can, by pursuing a certain method of breeding or cultivation, improve and in various ways modify the character of the different domestic animals and plants. By always selecting the best specimen from which to propagate the race, those features which it is desired to perpetuate become more and more developed; so that what are admitted to be real varieties sometimes acquire, in the course of successive generations, a character as strikingly distinct, to all appearances, from those of the varieties, as one species is from another species of the same genus. It is evident that both natural and artificial selection depends on adaptation and inheritance. The difference between the two forms of selection is that, in the first case, the will of man makes the selection according to a plan, whereas in natural selection the struggle for life and the survival of the fittest acts without a plan other than that the most adaptable organism shall survive which is most fit to contend with the circumstances under which it is placed. Natural selection acts, therefore, much more slowly than artificial selection, although it brings about the same end. Adaptation in the struggle for life is an absolute necessity.

In every act of breeding, a certain amount of protoplasm is transferred from the parents to the child, and along with it there is transferred the individual peculiar molecular motion. Adaptation or transmutation depends upon the material influence which the organism experiences from its surroundings, or its conditions of existence; while the transmission from inheritance is due to the partial identity of producing and produced organisms.

Organized beings, as a rule, are gifted with enormous powers of increase. Wild plants yield their crop of seed annually, and most wild animals bring forth their young yearly or oftener. Should this process go on unchecked, in a short time the earth would be completely overrun with living beings. It has been calculated that if a plant produces fifty seeds (which is far below the reproductive capacity of many plants) the first year, each of these seeds growing up into a plant which produces fifty seeds, or altogether two thousand five hundred seeds the next year, and so on, it would under favorable conditions of growth give rise in nine years to more plants by five hundred trillions than there are square feet of dry land upon the surface of the earth.

Slow-breeding man has been known to double his number in twenty-five years, and according to Euler, this might occur in little over twelve years. But assuming the former rate of increase, and taking the population of the United States at only thirty millions, in six hundred and eighty-five years their living progeny would have each but a square foot to stand upon, were they spread over the entire globe, land and water included. But millions of species are doing the same thing, so that the inevitable result of this strife cannot be a matter of chance. Evidently those individuals or varieties having some advantage over their competitors will stand the best chance to live, while those destitute of these advantages will be liable to destruction. Nature may be said (metaphorically) to choose (like the will of man in artificial selection) which shall be preserved and which destroyed.

That portion of the theory of development which maintains the common descent of all species of animals and plants from the simplest common origin, I have already stated with full justice should be called Lamarckism. Progress is recognized by all scientists to be a law of nature. Some of the more important facts which sustain the theory of development, I propose now to present as briefly as possible.