The Progress of the Century

by Unknown

ORGANIC EVOLUTION, ITS LAWS AND CAUSES

We now come to that branch of the subject which is the most important and distinctive of our age, and which, in popular estimation, alone constitutes evolution—the mode of origin of the innumerable species of animal and plant life which now exist or have ever existed upon the earth.

The origin of the different forms of life has till quite recent times been looked upon as an almost insoluble problem, although a few advanced thinkers, even in the eighteenth century, perceived that it was probably the result of some natural process of modification or evolution; but no force or law had been set forth and established in any way adequate to produce it until the publication of Darwin’s Origin of Species, in 1859. In the later editions of that work, Darwin has given a historical sketch of the progress of opinion on the subject. I shall, therefore, now only notice a few great writers which he has not referred to.

We have seen what an impossible and even ludicrous explanation had to be given by Lucretius; and from his day down to the middle of the eighteenth century no advance had been made. Either the problem was not referred to at all, or the theological doctrine of a special creation was held to be the only possible one. But in the middle of the eighteenth century the great French naturalist, Buffon, published his very important work, Histoire Naturelle, in fifteen volumes (1749–1767), in which, besides describing the characters and habits of all the animals then known, he introduced much philosophical and speculative thought, which would probably have been carried much further had he not felt obliged to conform to the religious prejudices of the age. We are indebted to Mr. Samuel Butler for having brought together all the important passages of Buffon’s voluminous and now little-read works bearing upon the question of evolution, and it is from his volume that I quote.

Buffon lays stress on the great resemblance of all mammalia in internal structure, showing that the most unlike creatures may be really alike structurally. He says: “The horse, for example—what can at first sight seem more unlike mankind? Yet when we compare man and horse, point by point and detail by detail, our wonder is excited rather by the resemblances than by the differences between them.” He then shows that all the parts of the skeleton agree, and that it is only in proportions, the increase of some bones and the suppression of others, that they differ, adding: “If we regard the matter thus, not only the ass and the horse, but even man himself, the apes, etc., might be regarded as forming members of one and the same family.” Then, after a few more illustrations, he remarks: “If we once admit that there are families of plants and animals, so that the ass may be of the family of the horse, and that the one may only differ from the other by degeneration from a common ancestor, we might be driven to admit that the ape is of the family of man, that he is but a degenerate man, and that he and man have had a common ancestor.... If it were once shown that we had right grounds for establishing these families, if the point were once gained that among plants and animals there have been even a single species which had been produced in the course of direct descent from another species, then there is no further limit to be set to the power of nature, and we should not be wrong in supposing that with sufficient time she could have evolved all other organized forms from one primordial type.”

This indicates clearly enough his own opinion, but to save himself from the ecclesiastical authorities he at once adds this saving clause: “But no! It is certain, from revelation, that all animals have alike been favored with the grace of an act of direct creation, and that the first pair of every species issued full formed from the hands of the Creator.”

Such examples of disarming religious prejudice are frequent, but he continually recurs to statements as to mutability which neutralize them. Here, for example, is a broad claim for nature as opposed to creation. He has been showing how variable are many animals, and how changes of food, climate, and general surroundings influence both their forms and their habits; and then he exclaims:

“What cannot nature effect with such means at her disposal? She can do all except either create matter or destroy it. These two extremes of power the Deity has reserved for Himself only; creation and destruction are the action of His omnipotence. To alter and undo, to develop and renew—these are powers which He has handed over to the charge of nature.”

Here we have a claim for the power of nature in the modification of species which fully comes up to the requirements of the most advanced evolutionist. It is remarkable, too, how clearly he perceived the great factors so important for the evolution of organisms, rapid multiplication, great variability, and the struggle for existence. Thus he remarks: “It may be said that the movement of nature turns upon two immovable pivots—one, the illimitable fecundity which she has given to all species; the other, the innumerable difficulties which reduce the results of that fecundity and leave throughout time nearly the same quantity of individuals in every species.” Here the term “difficulties” corresponds to the “positive checks” of Malthus, and to the “struggle for existence” of Darwin; and he again and again refers to variability—as when he says: “Hence, when by some chance, common enough with nature, a variation or special feature makes its appearance, man has tried to perpetuate it by uniting together the individuals in which it has appeared.”

As Buffon thus clearly understood artificial selection, thoroughly appreciated the rapid increase of all organisms, and equally well saw that their inordinate increase was wholly neutralized through such destructive agencies as hunger, disease, and enemies, and as, at the same time, he had such unbounded faith in the power of nature to modify animal and vegetable forms, we feel assured that this great writer and original thinker only needed freedom to pursue this train of thought a little further and he would certainly have anticipated Darwin’s great discovery of natural selection by a whole century. Even as it is we must class him as one of the great pioneers of organic evolution.

The next distinct step towards a theory of organic evolution was made by the poet Goethe at the very end of the eighteenth century, in his views of the metamorphosis of plants. He pointed out the successive modifications of the leaf which produced all the other essential parts of the higher plants—the simple cotyledons or seed leaves became modified into the variously formed leaves of the fully grown plants; these again were successively modified into the calyx, corolla, stamens, and ovary of the flower. He supposed this to be due to the increased refinement of the sap under the influence of light and air, and to indicate the steps by which the various parts of the flower had been developed. It was, therefore, a theory of evolution; but it was very unsatisfactory, inasmuch as it in no way accounted for the wonderful variety of the floral organs, or indicated any purpose served by the most prominent and conspicuous part of the flower, the highly colored and often strangely formed corolla. It was also erroneous in supposing that the corolla was a modified calyx, whereas it is now known to be a modification of the stamens.

Next came the great work of Lamarck in the first decade of the nineteenth century, in which he proposed a general system of evolution of the whole animal world. Hence he may be termed the first systematic evolutionist. His system has been rather fully described by Lyell, who, in his Principles of Geology, devotes a whole chapter to a summary of his doctrines; while Mr. Butler gives copious quotations in three chapters of his Evolution Old and New; and any one who is not acquainted with the original work of Lamarck should read these two authors in order to understand how wide was his knowledge, how ingenious his explanations, and in how many important points he anticipated the views both of Lyell and Darwin. But he was half a century in advance of his age, and his only alleged causes of modification—changed conditions, use and disuse, habit and effort—were wholly insufficient to account for the vast range of the phenomena presented by the innumerable minute adaptations of living organisms to their conditions of life. He even imputed all the modifications of domestic animals to the changed conditions of food and habits to which they have been subjected by man, making no reference to the use of selection by breeders, in this respect falling short of his great predecessor, Buffon.

The general laws which Lamarck deduces from his elaborate study of nature are these:

“Firstly. That in every animal which has not passed its limit of development, the more frequent and sustained employment of any organ develops and aggrandizes it, giving it a power proportionate to the duration of its employment, while the same organ, in default of constant use, becomes insensibly weakened and deteriorated, decreasing imperceptibly in power until it finally disappears.

“Secondly. That these gains or losses of organic development, due to use or disuse, are transmitted to offspring, provided they have been common to both sexes, or to the animals from which the offspring have descended.”

The whole force of this argument depends upon the second clause—the inheritance of those individual modifications due to use and disuse. But no direct evidence of this has ever been found, while there is a good deal of evidence showing that it does not occur. Again, there are many structures which cannot have been produced by use, such, for example, as the feathers of the peacock’s train, the poison in the serpent’s fangs, the hard shells of nuts, the prickly covering of many fruits, the varied armor of the turtle, porcupine, crocodile, and many others. For these reasons Lamarck’s views gained few converts; and although some of his arguments have been upheld in recent years, the fatal objections to his general principle as a means of explaining the evolution of organic forms has never been overcome.

Between the periods of Lamarck and Darwin many advances were made which clearly pointed to a general law of evolution in nature. Such were Sir William Grove’s lectures on the “Correlation of the Physical Forces,” in 1842; Helmholtz on the “Conservation of Energy,” in 1847; and Herbert Spencer’s essay on “The Development Hypothesis,” in 1852. This latter work was a complete and almost unanswerable argument for a natural process of continuous evolution of the whole visible universe, including organic nature, man, and social phenomena. It is further extended in the later editions of the author’s First Principles, which, as a coherent exposition of philosophy, co-ordinating and explaining all human knowledge of the universe into one great system of evolution everywhere conforming to the same general principles, must be held to be one of the greatest intellectual achievements of the nineteenth century. It left, however, the exact method of evolution of organisms untouched, and thus failed to account for those complex adaptations and appearances of design in the various species of animals and plants which have always been the stronghold of those who advocated special creation. This difficulty was met by Darwin’s theory of The Origin of Species by Means of Natural Selection, published in 1859, and the series of works that succeeded it; and to a brief sketch of this theory the remainder of our space must be devoted.