The Meaning of Evolution

by Samuel Christian Schmucker

Whether men with this conviction are merely reactionaries whose confidence is returning, or bold thinkers whose views will ultimately prevail, time alone can tell.

A second strong objection was brought against the theory of Natural Selection. Darwin declared that small variations in favorable directions are selected and become the starting point of new and better things. It is soon seen, however, that the effect of unaided Natural Selection would be but to mix new departures with the old forms, and soon swamp out any progressive tendency. Whenever a genius appeared, instead of finding a corresponding genius with which to pair, it mated with the average of its own species. Hence its offspring were nearer the average than it was, and their offspring still nearer. Thus whatever advantage the genius originally possessed gradually sank into the common level.

It was Moritz Wagner, a German naturalist, who first insisted that if favorable variations were to amount to anything these possessors must not only mate with others of their same kind, but must also be prevented from mating with the old average group. Accordingly, the belief arose that, under ordinary circumstances, variations returned to the common level. Wherever a varying group became separated by any barrier from mating with the rest of its species, and had only its own kind to pair with, a new species sprang up. This barrier might be a desert, or an impassable mountain range, an arm of the sea, or anything else that the animal could not, or would not, cross. Isolated in this way, the little group that had an advantage in a different direction could develop its tendencies, and a new species would be made of what had been previously only a geographical race. In this matter of geographical isolation Wagner is very strongly supported by the American zoölogist, David Starr Jordan, who believes that no two closely related species of animals ever occupied the same geographical area. Both Wagner and Jordan are ardent admirers of Darwin and his theory of natural selection, but both believe that it is necessary to add the idea of isolation in order to make natural selection effective.

George John Romanes, a British naturalist, has added to Wagner's idea of isolation, the expanded conception that there may be isolations that are not geographical. For this phase, Romanes has coined the term physiological isolation. Something in the structure or habit of the animals with the new variation prevents them from mating with the older type. Occasionally it is a difference in the structure of the reproductive organs themselves. This, however, is not the only possible divergence. The mating season in one group may come earlier than that of the other, or may come during the day, while the main group is in the habit of mating at night. Anything which keeps some members of a species separate in their mating from the rest, will result in the course of a longer or shorter time, says Romanes, in the formation of a new species.

A third great objection was raised against Darwinism. The theory said that only useful variations were selected by nature. It was asserted by objectors that the earliest beginnings of any variation must be too slight to be useful, or as the term went, to have selective value.

It has been noticed by a number of naturalists that certain animals seem to carry the development of a peculiarity altogether too far. It is seen for instance that in the Irish Elk, which has for some time been extinct, the horns were so enormous as to be a source of danger rather than of assistance to their owner. It was said that the tendency to produce heavy horns had gained, as it were, a sort of momentum, and that this impulse had carried the development beyond a safe limit. The Irish Elk became extinct because his horns were too heavy. During the Mesozoic period the reptiles grew too large. They seemed to have carried size to a point at which it became a danger instead of a help. They completely passed out of existence, leaving behind them only very much smaller reptiles.

Eimer, of Germany, has based on facts like these his theory of Orthogenesis. He says that variations in animals are not indefinite and in every direction, but that they follow along clear and definite lines. These lines, in the case of the elk and of the Mesozoic reptiles, developed too far, but ordinarily the effect of such a tendency is distinctly beneficial to the animal. It particularly assists in carrying on for a time the variations which have not yet become useful to the animal. It has always been difficult on Darwinian principles to understand how the beginnings of the useful variations could be selected before they were strong enough to be of actual value to the animal. This tendency to variations in certain directions instead of at random would account for such early development. This theory of Orthogenesis has not figured very strongly in the history of the movement, but it recurs at intervals.

Both in America and France there is a constant tendency on the part of zoölogists to return to the Lamarckian idea that it is the use of an organ that develops it, its disuse that makes it fade away. This is undoubtedly true of the individual, and although Weissman insists that it is useless to the species as a whole, many zoölogists are slow to relinquish entirely the idea that somehow these favorable developments become reproduced in the offspring.

Professor Cope, the American paleontologist, was a strong believer in the effect of activity, both upon the individual and upon his descendants. He believed that the insistent beating of the foot of an animal upon the hard soil of the drying Tertiary plateau, had influenced the production of a firmer nail, which spread around the entire end of the toe and made the hoof of the ungulate. He believed that the use of the teeth in grinding produced a stronger and better molar tooth, and that the offspring shared in this advantage. Since Weissmann's time, however, every Lamarckian feels it necessary to suggest some method by which the altered body of the parent can produce modifications in the germ plasms from which the young are to spring. One of our later biologists begins to talk of some effect comparable with wireless telegraphy or induced electricity. He believes that organs in the adult, not necessarily by direct action, but by action from a distance, may alter the germ. Of this, there is no proof at present. Others have suggested that just as the ductless glands pour into the blood chemical substances which materially affect the growth and development of other portions of the body, so similar enzymes, or other chemical substances, may be sent into the blood, which subsequently bathes the germ cells of the coming generation and produces the change. But of this, again, there is no proof. We may believe that acquired characters are transmitted, but we certainly do not have a very clear idea as to how it can be done.

One of the strongest objections to Darwin's idea of evolution by natural selection of small and favorable variations, is that the process is too inconceivably slow to account for the enormous progress which has been made. The answer has always been that our observation ran back so short a time that we really have no clear idea of how rapid evolution may have been. Again, it has been answered that transitional geological periods, in which there is much change in the physical geography of a country, will produce more rapid evolution than we at present are experiencing.