The Meaning of Evolution

by Samuel Christian Schmucker

Why this should be so is one of the most profound problems of biology. Nothing but the fact that the process has gone on under our eyes for so long a time could blind us to its marvelous character. To open the egg of a chicken and examine it by the most refined methods known to science is to find in it absolutely nothing that could be by the widest stretch of the imagination considered anything like a chicken. The biologist who has examined such eggs before and knows them in all stages of the process may recognize in an egg which had been incubated for a short time something which his previous experience tells him will become a chicken. But it has not the faintest resemblance to a chicken until later in its development. In early spring one may gather pond snails from any country stream and place them in an aquarium. The change from the cold water on the outside to the warmer water of the aquarium and the temperate climate of the room hastens the process which in the stream would not take place until later. In a short time one may find fastened to the glass side of the aquarium the little mass of transparent jelly which surrounds and protects the delicate eggs of these creatures. Fastened as they are it is easy to direct a magnifying glass so as to observe the change which goes on within these transparent eggs. It is even possible to apply a microscope in such a way as to watch the transformation under the low power of the glass. At first the eggs are as clear as water, having at the center a slightly yellowish spot. This central mass divides and subdivides until the separated sections grow so small and numerous as to lose individuality. Then the mass begins to press out here and dent in there. After a little while a double line of fine, hairlike projections runs around the creature. These hairs wave in such fashion as to make the embryo snail revolve slowly in its egg. A little later and swellings become more pronounced over the surface. One side flattens; the rotary motion stops; eyes appear at the front of the animal; a hump on the back begins to be covered with a shell, and the little creatures, pushing from the jelly, start their life journey on the side of the aquarium. Why did it happen? How did it happen? Here we have seen creation at work. Here surely the hand of the Creator is working in the only sense in which the Creator may be properly said to have a hand. How the history of the substance out of which the egg was produced provides for the future development of that egg no man has yet clearly said. This is not to say that we shall never know, still less is it to say that this can never be known. Ralph Waldo Emerson has said that there is no question propounded by the order of nature which the order of nature will not at some time solve. If he is right, and I believe he is, we shall at some time know how it is that this egg produces this snail. But, as I said before, nothing but the frequency with which the process goes on under our eyes could possibly blind us to the marvel of it.

The regularity with which each animal reproduces its kind is no more surprising than the faithfulness of that reproduction. Some of our birds have wonderful markings on their plumage. It is astonishing to see with what fidelity the feather of a bird may reproduce the corresponding feather of its parent. It will occur to everyone how, in the human family to which he belongs, there is some little peculiarity which, while not appearing in every member of the family, when it does appear is remarkably uniform. It may be only the droop of an eyelid, it may be a tendency to lift one side of the lip more than the other, it may be the peculiar shape of a certain tooth in the set, and yet when it appears it comes with astonishing similarity in all who possess it. So much for the principle of Heredity.

The second great underlying idea is known by the name of Variation. We have just been dwelling on the regularity with which parents produce offspring like themselves. We must now draw attention to the fact that, while it is true animals must absolutely belong to the same genus or species, even to the same variety, none the less no animal is exactly like his parents. Furthermore, in a group of animals produced at the same time from the same parent each one will have at least some small point in which he differs from every other one in the group. Two animals may look alike at first to the undiscerning eye, but a keen analysis of the measurements of the various parts of their bodies will show distinct differences. This is quite as true among lower animals. A toad may lay a double string of four hundred eggs which may be fertilized by the same male at the same time. These eggs may develop into tadpoles in the same pool not over a foot square. Within a few weeks these little toads may have gained their legs, lost their tails, and all may have left the water and taken to the ground upon the same day. Already the careful observer will notice differences among them. Some are larger than others, having grown more rapidly even though their surroundings were exactly the same; others are more skillful in their peculiar method of throwing the tongue at an insect they wish to catch. Still others will be differently colored. They might be arranged to show a considerable gradation between the lightest and the darkest of the group, though there may not be anywhere in the row a considerable gap. It is variation in animals of the same parentage and same surroundings which in the mind of Mr. Darwin made evolution possible. He always favored the idea that it was the continuous accumulation of these small variations that finally produced the profound changes which mark the new species. He admitted the possibility of the occasional appearance of those more distinct leaps in variation on which the present school of mutationists so strongly insists; but he believed them to be less influential, in the general trend of evolution, than the slower but much more frequent variations.

One of the most complicated and perplexing problems in the biology of to-day is the question of the origin of these variations. It is quite as hard to understand as is the method by which animals produce their own kind. No problem is being more earnestly studied. Suppositions we have in considerable number, and two of these at least may reasonably be mentioned. We will consider first the less certain theory. There is nothing in the egg that in the remotest degree resembles its parent. The old idea that every acorn had in it a miniature oak which only needed to unfold itself, or that the hen's egg had within it a miniature chick which only needed the warming process in order to make it evident, could not possibly survive the invention of the microscope. We may not, and we certainly do not, know everything that is in one of these eggs, but we do know most certainly that what is there has no resemblance to what it will be in time. The biologist finds in the nucleus or central core of every growing and reproducing cell certain minute bodies which Weissmann believes do much to determine the growth of the rest of the cell. He believes also that there are many more such "determinants" than are necessary for the reproduction of the cell. Each of these determinants may be fitted to produce slightly different results, but what decides which of them shall have its own way is quite uncertain. It may be that one determinant happens to be more favorably placed than others in the cell and that it has consequently secured more of the nourishment that comes to the cell in the blood of its parent. If this is true it would certainly be favored in the competition. We are becoming quite certain that whatever variations arise really start in the egg. The simplest conception as to the cause of variation would seem to be varied experience. One man trains his brain, another his hand; and in each case the organ so trained develops. But science is strongly of the mind that such influence does not reach the next generation.

A musician may have taught his fingers to be nimble; may have given them speed of motion and precision in their action. No child of his born after he acquired this wonderful facility of execution is any more likely to be a skilled musician than a child born before he had ever practiced enough to be anything more than a crude performer. Science is nearly certain that his children are just as likely to be talented along musical lines if he himself never had become a musician, simply because he had it in him to be a musician. In other words, they may inherit the talent which he developed, but they inherited it not because he developed it, but because it was in him to be developed. This is in accordance with the famous principle that there is no inheritance of acquired characters. We shall touch this question a little more fully in a later chapter, in speaking of the development of the evolution theory since Darwin's time.

If we are right in this matter, and we certainly are nearly right, variation must take place for the most part in the germ. These variations may not show until the animal has grown up, but they must have taken place among the determinants in the germ cell or they would not reappear in subsequent generations.

There is another process by which new variations may arise and which is more easily understood. It is the method of double parentage. The Barred Plymouth Rock chicken had its origin in such a double ancestry. The one parent was a Black Java whose color has disappeared entirely in the cross, but whose single comb with its few large points comes out clearly in the newly produced fowl. The other parent was a Barred Dominique. It is to this parent that the Plymouth Rock owes the interesting cross markings on its feathers. The comb on the head of the Barred Dominique is of the type known as the rose-comb, having many rows of slight projections. This has completely disappeared from the Plymouth Rock fowls. I am told that the skilled chicken fancier can tell, concerning many points in this fowl, to which of the crossed ancestors each quality is due. To a certain extent it is undoubtedly true that here we have the secret of the origin of many of those interesting people whom we are pleased to call geniuses. They may not possess any qualities not clearly discernible in various of their near ancestors, but in them we find what we, for the lack of a better understanding, call chance combination in one individual of the finer qualities of many ancestors, and this individual is so placed in life as to have these qualities developed and strengthened.

Charles Darwin, humanly speaking, may be accounted for as the happy combination of a double heredity and a favorable environment. He inherited the scientific inclinations of his grandfather, Erasmus Darwin, and the patient, sturdy honesty of his other grandfather, Josiah Wedgwood. These developed under the stimulus of the long five-year voyage, face to face with the world of nature. This happy complex produced the master biologist. To believe that he came about purely by chance requires a great stretch of the imagination. "There's a divinity that shapes our ends."

We have endeavored to make clear two of the basal ideas underlying evolution. One of these is responsible for the continued production of animals or plants of the same kind, preventing the world from becoming a wild kaleidoscopic and fantastic dream. Heredity is the conservative force of nature. The other idea underlies the development of new departures which keep the world from being a dull, dead, unending repetition of the same monotonous material. Variation is the progressive tendency in nature.

The third basal idea is that of Multiplication. Animals and plants multiply; they do not simply increase, they increase in a geometrical ratio. Anyone who has worked out one of these geometrical ratios knows how wondrously they mount up. There is an old familiar story of the blacksmith who asked the price at which the stranger would sell the horse he was shoeing. The owner of the horse replied that, if the blacksmith would give him one penny for the first nail he drove into the shoe, two for the second, four for the third, and so on, he might have the horse. No hundred horses in the world taken together have ever brought such a price as the blacksmith would have had to pay for the animal on which he was working. This is no circumstance to the awful story of what would happen to the earth if any animal could multiply unrestricted. The usual number of eggs laid by a mother robin for a single brood is four, and she may produce two broods in one season. This would mean that the original pair had produced eight offspring, four times their own number. If we can imagine these mating the next year and producing their kind in the same proportion; and, if we further suppose that each robin needs a space one hundred feet square from which to gather his food, we realize the astonishing fact that in fifteen years every patch one hundred feet square in Pennsylvania and New York would each have its resident robin, while the following season would find a robin on every similar patch from Maine to the Carolinas. Of course this could never happen, this is simply what would happen if all the robins could grow to maturity and reproduce at the normal ratio. But the robin is a comparatively slow producer.