The Meaning of Evolution

by Samuel Christian Schmucker

Our turtles are more prolific. Twenty eggs would probably not be an unusual number. If we could imagine a turtle to live in the sea and to produce at this rate; and, if each turtle should need as much room each way as the robin, and a depth of water equal to its width, before the robins had spread over New York and Pennsylvania the turtles would have filled all the seas of the globe. Frogs are even more remarkable in this respect. Two hundred eggs is not an uncommon number. If each frog required a space twenty-five feet square on which to subsist, the entire earth would be more than covered with them within six years. It is ludicrous to think of such numbers, especially when we realize the hundreds of thousands of kinds of animals there are in the world, each of which is also multiplying, and it becomes evident at once that only an infinitely small proportion of all these creatures can possibly survive. This, then, is multiplication.

Here comes into play the fourth basal idea in Mr. Darwin's explanation. This is the part of Selection. When man produces new varieties of animals he does it by picking out from his flocks or his herds such as conform most nearly to his idea of what is desirable. These he mates, and from their progeny he selects the ones that suit him best. Generation by generation he gets his domesticated animals to conform more nearly to the standard of his desires. Natural selection works in exactly similar fashion. Of all the eggs that are produced by the animals at large in nature an overwhelming proportion never develop at all. They dry up, are eaten by their enemies, find no suitable place or time for development and decay, or are overtaken by some other calamity. Of the animals which emerge from the remainder an overwhelming majority come to an untimely end within the first few days of life. Each has countless enemies which prey upon him, and these have scarcely devoured him before they themselves become the prey of some stronger creature. Until Mr. Darwin gave us his elemental idea it was taken for granted that it was a matter of pure accident which survived and which yielded in the struggle and cares of life. It was Darwin who showed us that in this tremendous struggle against those of his own kind in the search for the same food, against the elements, in securing a mate, any animals possessing a superiority, however slight, must have some little advantage in the battle. Certainly, where so many must utterly fail, only those could possibly succeed who were well fitted to the circumstances in which they must live. We used to think animals were destroyed by the "accidents" of life and no one could foretell accidents. Mr. Darwin made clear that it was not a question of chance. That which might happen to any individual animal might be what we, not knowing the process, called accident, and yet there could be no possible doubt that those who succeeded were better fitted to battle with life than those who failed, and that their success was due primarily to their being thus advantaged. Consequently, if generation by generation the so-called accidents of life are constantly eliminating the unfit in overwhelming proportions, not only must the positively unfit disappear, but even the less fit. The more keen the struggle, the fewer could survive and the fitter they must be to survive at all. This is Selection. These, then, are Darwin's four great factors of evolution: Heredity, Variation, Multiplication, Selection.

From these it results that the animals and plants naturally become better adapted to the situation in which they are placed. When, as is constantly happening through the history of the earth, a change occurs in the physical geography of any region, when a plain is lifted to be a plateau, or a mountain chain is submerged until it becomes a row of small islands, this alteration will produce uncommon hardships among animals, even though they were well fitted to the old conditions. Any animal or any species of animals which meets such a calamity has before it only three possible outcomes of the struggle. First it may be plastic enough and it may vary enough in the right direction to adjust itself to the changed conditions. In this case it and a favored few like it will occupy the altered territory. The second possibility is that it may migrate while the actual change is going on, thus remaining in the sort of situation suited to it and its kind. The third possibility is the one which overtakes a great majority of animals—they die. Even the entire line dies out, and the strata of the rocks are filled with the bones, shells, and teeth of such as have met this fate. They have become extinct.

Thus far in this chapter we have been considering the influences under which it is conceivable that animals should advance. There is no question whatever that there are too many animals born, nor is there any possible question that a very large proportion of them must certainly die. There is equally no doubt that every animal produces after its own kind, and that its offspring, while they resemble it closely, still vary a little from it and from each other. This fact is perfectly plain to the most superficial observer who thinks on the matter at all. It is not so plain, nor is it easily demonstrated, that all of these acting together do surely, even if slowly, alter the form and behavior of the animal world. It is difficult to prove that there is going on under our eyes a steady and real improvement in the adaptation of the animals and plants around us to the situation in which they are placed. As far back as man's memory runs they seem to have been about what they now are; as far even as man's historical record runs they seem to have suffered no great alteration. The Egyptian of the old tombs is much like the Egyptian of the same rank to-day. The African of the tombs has the African features of to-day. Under such circumstances it is hard to prove that there is a steady and undoubted advance. For the most part the balance of the animal world is fairly even, and any species does not ordinarily change rapidly enough or migrate widely enough to show us its new features. It is difficult to see the struggle which we are so sure is going on. The life of animals is so hidden in many of its details that their joys and sorrows, if such we may call them, scarcely fall under our observation. Now and then an opportunity comes to see the process of adaptation work itself out. The struggle for existence begins anew and is carried on with special vigor, with victory, temporary or permanent, to one of the participants in the struggle.

The opportunity to observe such a change is presented in the United States by the introduction of the so-called English sparrow. This little creature, received at first with such joy, soon became the object of an almost bitter hatred on the part of very many people. This is really due to the fact that this bird is one of nature's darlings and thoroughly succeeds where it has an even chance.

The number of birds of any particular species which a region will support seems to be fairly definite. If a species is especially protected until it becomes unusually abundant, the removal of the protection commonly brings it down promptly to its original numbers. On the other hand, an accident of severe character or a special persecution may much diminish the number of the species, and still it will, within a comparatively few years, return to its previous abundance.

The inhabitants of Florida who own orange groves will never forget the winter of '94–5. A bitter cold wave swept along the coast and killed such large numbers of orange trees as almost to cut Florida out of the orange market and to open the gate to California, who was eagerly offering her fruit. This same frost caught the migrating blue birds and killed them by the thousands. When spring came bird-lovers throughout the eastern United States found an astonishing scarcity of these favorites. It was feared that with numbers so small they could not possibly compete with their enemies and with whatever untoward circumstances should be their lot. But there is room in this environment for a definite number of bluebirds. When this number was suddenly reduced the chances to make a bluebird's living were so wondrously multiplied that young bluebirds had such an opportunity in life as their fellows had not had for many long years. Accordingly they thrived as never before, and, of their progeny, a larger proportion lived to the following year. It was only a few years before the number of bluebirds had risen. Now we probably have as many as we have had for a long time past. I cite this simply to show that a region can support a certain number of animals of any one particular kind, and that the animal is likely to multiply, if given a fair chance, until it has reached such proportions. Now to my story of the rapid development of a newcomer.

In the year 1850 a resident of Brooklyn came home from a trip to Europe. He was a lover of birds, and while in Europe had been particularly attracted, no one now knows quite why, to the common House Sparrow, as it should be called. It is no more abundant in England than in many parts of the continent of Europe. A name that has been used for a long time is very hard to cast aside, and we shall probably continue to mistakenly call him the English Sparrow to the end. Our Brooklyn traveler brought home with him from Europe eight of these interesting little birds and succeeded in inducing his colleagues in a scientific society to share his interest in them. Not wishing to commit the newcomers suddenly to the rigors of the American winter, these men built a large cage for the sparrows, meaning to set them free in the spring. For some reason or other when the winter was over the birds were all dead, and this first attempt to introduce the sparrow into America failed entirely. The little bird had won so many friends that his success was now sure. Finding a favorable opportunity, these Brooklyn men dispatched an order to a man in Europe, asking him to supply them with one hundred English sparrows. The consignment came in good shape and the birds were liberated on the edge of Brooklyn. This was the first of a number of introductions. A little later New York City sent for two hundred and twenty of these interesting creatures and turned them loose in her parks, while Rochester, with what was then considered great public spirit, purchased one hundred for herself. But the most progressive city in this respect was Philadelphia. She had long been troubled with the spanworm on her trees. This detestable larva had the unpleasant fashion of lowering itself by a long silken thread from the shade trees then so abundant in that beautiful city. The spanworms traveling around over the clothing of the passersby were so objectionable to everybody that it was with greatest delight that Philadelphia heard of the new birds which ate the pest. One wonders why some ornithologist did not look at the bird long enough to see that it had the sort of a bill characteristic of birds that eat seeds. It is true that most birds feed their young on insects, hence there is a time when any bird is apt to be insectivorous. But the structure of the sparrow's bill, like that of all finches, should have warned these bird-lovers that the sparrow was not to be depended upon to earn his living by catching worms. It is easy, however, to be wise after the event. Philadelphia believed she was engaging in a particularly advanced movement when she imported from England one thousand English sparrows, nearly as many as were liberated by all other cities together. These birds were turned loose among the shady streets and wide spreading parks of the City of Brotherly Love.

It is a serious matter lightly to disturb the balance of nature by the introduction of a new species. It is true that the sparrow did eat some spanworms and for a while enthusiastic bird-lovers hoped that here was the solution of the difficulty. Philadelphians will also remember that, with the spanworm removed from competition, the tussock moth, whose caterpillar carries on his back a series of yellow, red, and black paint brushes, at once become the permanent parasite of the long-suffering shade trees. This caterpillar is covered with bristling hairs, very closely set. Almost any bird objects to hair in his victuals; and this particular larva has hair more than ordinarily objectionable, for it irritates wherever it pricks the sensitive skin. This coating seems to protect the caterpillar from the sparrow, with the result that Philadelphia's trees were soon nearly defoliated by this comparatively new pest, worse than the spanworm. With the paving of the city's highways and the consequent shutting off of the air from the roots, the trees have largely disappeared from the streets of Philadelphia. With them have gone a fair portion of the tussock worms, but the sparrow holds his own. Here is a new bird in the field, and the struggle for existence on the part of every other kind of bird is now more complicated and severe. The sparrow can live where the rest of the birds have no possible chance. He throve so well in this country that by 1875 he had spread over five hundred square miles in the neighborhood of our larger Eastern cities. Thus far almost everybody was pleased with the new introduction. Within the next five years he had spread over more than fifteen thousand square miles, and wise men were beginning to feel doubtful of the virtues of their aforetime friend. When by 1885 more than five hundred thousand square miles had been occupied by the enterprising little fellow, there remained no longer a doubt in the minds of most people that the sparrow was an unmitigated nuisance and great fears were entertained that he had multiplied to such an extent as to be a serious menace. Here, then, is a modern instance under our own eyes of a victory in the struggle. If the sparrow has multiplied rapidly, while all the other birds have either only held their own or even have diminished in numbers, it is quite evident he must be better fitted to the conditions than they are. What are his fit points? Why does he succeed while others fail? The thoughtful bird-lover will have little trouble in understanding at least some of his victory-winning characteristics. How did he come to be almost the only bird who can live in large numbers in our great cities, without losing his ability to get along in less crowded situations?

In the first place this interesting bird is a clannish fellow. He has lost the ordinary sparrow habit and has come to like to live in crowded groups. Seclusion is not at all to his taste, and if there are only a few sparrows in the neighborhood those few will most certainly be found living near each other. One of the early adaptations of the sparrow to his city surroundings was the ability to find for himself a considerable proportion of his food in the undigested seed that could be picked up from the droppings of the horses. This naturally led the surplus sparrows out through the many thoroughfares leading from any large city. Where horses went sparrows could follow. Accordingly along the great lines of travel this bird found the simple path by which he could enter new territory. Meanwhile box-cars came into our large cities with freight. Sometimes they had carried grain, sometimes cattle. In either case it was not unlikely that a certain amount of grain should be found scattered over the floor of such cars. The sparrow visited these cars for the grain, and it must have been no infrequent accident that a door should be shut upon a group of sparrows, especially in inclement weather, when they were apt to be huddled in a dark corner of the car. These prisoners would be carried to the destination of the car and there liberated, thus producing a new center of what we are now inclined to call infestation. By such means the English sparrow has spread over much the larger portion of the American continent. Few birds are bold enough to visit a railroad car. Of the few who might be tempted, most are timid enough to fly on the first approach of man. Hence they fail to gain this chance of spreading. They must remain in the old crowded home. Meanwhile the sparrow, thus transported, finds a new home with fewer or no sparrows. The struggle is less keen. More of his kind can live. His boldness has been here a fit quality and has helped him in the race.