Having discussed the early services of German and French nature-philosophy in establishing the doctrine of descent, we turn to the third great country of Europe, to free England, which during the last ten years has become the chief seat and starting-point for the further working out and definite establishment of the theory of development. Englishmen, who now take such an active part in every great scientific progress of humanity, and are the first to promote the eternal truths of natural science, at the beginning of the century took but little part in the continental nature-philosophy and its most important progress, the Theory of Descent. Almost the only earlier English naturalist whom we have here to mention is Erasmus Darwin, the grandfather of the reformer of the Theory of Descent. In 1795 he published, under the title of “Zoonomia,” a scientific work in which he expresses views very similar to those of Goethe and Lamarck, without, however, then knowing anything about these two men. It is evident that the Theory of Descent at that time pervaded the intellectual atmosphere. Erasmus Darwin lays great stress upon the transformation of animal and vegetable species by their own vital action and by their becoming accustomed to changed conditions of existence, etc. Next, W. Herbert, in 1822, expressed the opinion that species of animals and plants are nothing but varieties which have become permanent. In like manner Grant, in Edinburgh, in 1826, declared that new species proceed from existing species by continued transformation. In 1841 Freke maintained that all organic beings must be descended from a single primitive type. In 1852 Herbert Spencer demonstrated minutely, and in a very clear and philosophic manner, the necessity of the Doctrine of Filiation, and established it more firmly in his excellent “Essays,” which appeared in 1858, and in his “Principles of Biology,” which was published at a later date. He has, at the same time, the great merit of having applied the theory of development to psychology, and of having shown that the emotional and intellectual faculties could only have been acquired by degrees and developed gradually. Lastly, we have to mention that in 1859 Huxley, the first of English zoologists, spoke of the Theory of Descent as the only hypothesis of creation reconcilable with scientific physiology. The same year produced the “Introduction to the Flora of Tasmania,” in which Hooker, the celebrated English botanist, adopts the Theory of Descent, supporting it with important observations of his own.
All the naturalists and philosophers with whom we have become acquainted in this brief historical survey, as men adopting the Theory of Development, merely arrived at the conception that all the different species of animals and plants which at any time have lived, and still live, upon the earth, are the gradually changed and transformed descendants of one or some few original and very simple prototypes, which latter arose out of inorganic matter by spontaneous generation. But none of them succeeded in placing this fundamental element of the doctrine of descent in relation with some cause, nor in satisfactorily explaining the transformation of organic species by the true demonstration of its mechanical antecedents. Charles Darwin was the first who solved this most difficult problem, and this forms the broad gulf which separates him from his predecessors.
The special merit of Charles Darwin is, in my opinion, twofold: in the first place, the doctrine of descent, the fundamental idea of which was already clearly expressed by Goethe and Lamarck, has been developed by him much more comprehensively, has been traced much more minutely in all directions, and carried out much more strictly and connectedly than by any of his predecessors; and secondly, he has established a new theory, which reveals to us the natural causes of organic development, the acting causes (causæ efficientes) of organic form-production, and of the changes and transformations of animal and vegetable species. This is the theory which we call the Theory of Selection, or more accurately, the Theory of Natural Selection (selectio naturalis).
When we reflect that (with the few exceptions above mentioned) the whole science of Biology, before Darwin’s time, was elaborated in accordance with the opposite views, and that almost all zoologists and botanists regarded the absolute independence of organic species as a self-evident inference from the results of all study of forms, we shall certainly not lightly value the twofold merit of Darwin. The false doctrine of the constancy and independent creation of individual species had gained such high authority, was so generally recognized, and was, moreover, so much favoured by delusive appearances, accepted by superficial observation, that, indeed, no small degree of courage, strength, and intelligence was required to rise as a reformer against its omnipotence, and to dash to pieces the structure artificially erected upon it. But, in addition to this, Darwin added to Lamarck’s and Goethe’s doctrine of descent the new and highly important principle of “natural selection.”
We must sharply distinguish the two points—though this is usually not done—first, Lamarck’s Theory of Descent, which only asserts that all animal and vegetable species are descended from common, most simple, and spontaneously generated prototypes; and secondly, Darwin’s Theory of Selection, which shows us why this progressive transformation of organic forms took place, and what causes, acting mechanically, effected the uninterrupted production of new forms, and the ever increasing variety of animals and plants.
Darwin’s immortal merit cannot be justly estimated until a later period, when the Theory of Development, after overthrowing all other theories of creation, will be recognized as the supreme principle of explanation in Anthropology, and, consequently, in all other sciences. At present, while in the hot contest for truth the name of Darwin is the watchword to the advocates of the natural theory of development, his merits are inaccurately appreciated on both sides, for some persons overestimate them as much as others underestimate them.
His merit is overestimated when he is regarded as the founder of the Theory of Descent, or of the whole of the Theory of Development. We have seen from the historical sketch in this and the preceding chapters, that the Theory of Development, as such, is not new; all philosophers who have refused to be led captive by the blind dogma of a supernatural creation, have been compelled to assume a natural development. But the Theory of Descent constituting the specially biological part of the universal Theory of Development, had already been so clearly expressed by Lamarck, and carried out so fully by him to its most important consequences, that we must honour him as the real founder of it. Hence it is only the Theory of Selection, and not that of Descent, which may be called Darwinism; but this is in itself of so much importance, that its value can scarcely be overestimated.
Darwin’s merit is naturally underestimated by all his opponents. But it is scarcely possible in this matter to point to scientific opponents, who are entitled by profound biological culture to pronounce an opinion. For among all the works opposed to Darwin and the Theory of Descent yet published, with the exception of that of Agassiz, not one deserves consideration, much less refutation; all have so evidently been written either without thorough knowledge of biological facts, or without a clear philosophical understanding of the question in hand. We need not trouble ourselves at all about the attacks of theologians and other unscientific men, who really know nothing whatever of nature.
The only eminent scientific adversary who still remains opposed to Darwin and the whole theory of development is Louis Agassiz; but the principle of his opposition in reality deserves notice only as a philosophical curiosity. In a French translation of his “Essay on Classification,”[(5)] which we have spoken of before, published in Paris in 1869, Agassiz has most formally announced his opposition to Darwinism, which he had previously expressed in many ways. To this translation he has appended a treatise of sixteen pages, bearing the title, “Le Darwinisme. Classification de Haeckel.” This curious chapter contains the most wonderful things; as, for example, “Darwin’s idea is a conception à priori. Darwinism is a burlesque of facts. Science would renounce the claim which it has hitherto possessed to the confidence of earnest minds if such sketches were to be accepted as indications of a true progress.” The following passage, however, is the climax of this strange polemic: “Darwinism shuts out almost the whole mass of acquired knowledge in order to retain and assimilate to itself that only which may serve its doctrine.”
Surely this is what we may call turning the whole affair topsy-turvy! The biologist who knows the facts must be astounded at Agassiz’s courage in uttering such sentences—sentences without a word of truth in them, and which he cannot himself believe! The impregnable strength of the Theory of Descent lies just in the fact that all biological facts are explicable only through it, and that without it they remain unintelligible miracles. All our “laborious knowledge” in comparative anatomy and physiology—in embryology and palæontology—in the doctrine of the geographical and topographical distribution of organisms, etc., constitutes an irrefutable testimony to the truth of the Theory of Descent.