CHAPTER II.
SCIENTIFIC JUSTIFICATION OF THE THEORY OF DESCENT. HISTORY OF CREATION ACCORDING TO LINNÆUS.
The Theory of Descent, or Doctrine of Filiation, as the Monistic Explanation of Organic Natural Phenomena.—Its Comparison with Newton’s Theory of Gravitation.—Limits of Scientific Explanation and of Human Knowledge in general.—All Knowledge founded originally on Sensuous Experience, a posteriori.—Transition of a posteriori knowledge, by Inheritance, into a priori knowledge.—Contrast between the Supernatural Hypotheses of the Creation according to Linnæus, Cuvier, Agassiz, and the Natural Theories of Development according to Lamarck, Goethe, and Darwin.—Connection of the former with the Monistic (mechanical), of the latter with the Dualistic Conception of the Universe.—Monism and Materialism.—Scientific and Moral Materialism.—The History of Creation according to Moses.—Linnæus as the Founder of the Systematic Description of Nature and Distinction of Species.—Linnæus’ Classification and Binary Nomenclature.—Meaning of Linnæus’ Idea of Species.—His History of Creation.—Linnæus’ view of the Origin of Species.
The value which every scientific theory possesses is measured by the number and importance of the objects which can be explained by it, as well as by the simplicity and universality of the causes which are employed in it as grounds of explanation. On the one hand, the greater the number and the more important the meaning of the phenomena explained by the theory, and the simpler, on the other hand, and the more general the causes which the theory assigns as explanations, the greater is its scientific value, the more safely we are guided by it, and the more strongly are we bound to adopt it.
Let us call to mind, for example, that theory which has ranked up to the present time as the greatest achievement of the human mind—the Theory of Gravitation, which Newton, two hundred years ago, established in his Mathematical Principles of Natural Philosophy. Here we find that the object to be explained is as large as one can well imagine. He undertook to reduce the phenomena of the motion of the planets, and the structure of the universe, to mathematical laws. As the most simple cause of these intricate phenomena of motion, Newton established the law of weight or attraction, the same law which is the cause of the fall of bodies, of adhesion, cohesion, and many other phenomena.
If we apply the same standard of valuation to Darwin’s theory, we must arrive at the conclusion that this theory, also, is one of the greatest achievements of the human mind, and that it may be placed quite on a level with Newton’s Theory of Gravitation. Perhaps this opinion will seem a little exaggerated, or at any rate very bold, but I hope in the course of this treatise to convince the reader that this estimate is not too high. In the preceding chapter, some of the most important and most general phenomena in organic nature, which have been explained by Darwin’s theory, have been named. Among them are the variations in form which accompany the individual development of organisms, most varied and complicated phenomena, which until now presented the greatest difficulties in the way of mechanical explanation, that is, in the tracing of them to active causes. We have mentioned the rudimentary organs, those exceedingly remarkable structures in animals and plants which have no object and refute every teleological explanation seeking for the final purpose of the organism. A great number of other phenomena might have been mentioned, which are no less important, and are explained in the simplest manner by Darwin’s reformed Theory of Descent. For the present I will only mention the phenomena presented to us by the geographical distribution of animals and plants on the surface of our planet, as well as the geological distribution of the extinct and petrified organisms in the different strata of the earth’s crust. These important palæontological and geographical phenomena, which were formerly only known to us as facts, are now traced to their active causes by the Theory of Descent.
The same statement applies further to all the general laws of Comparative Anatomy, especially to the great law of division of labour or separation (polymorphism, or differentiation), a law which determines the form or structure of human society, as well as the organization of individual animals and plants. It is this law which necessitates an ever increasing variety, as well as a progressive development of organic forms. This law of the division of labour has, up to the present time, been only recognized as a fact, and it, like the law of progressive development, or the law of progress which we perceive active everywhere in the history of nations (as also in that of animals and plants), is explained by Darwin’s Doctrine of Descent. Then, if we turn our attention to the great whole of organic nature, if we compare all the individual groups of phenomena of this immense domain of life, it cannot fail to appear, in the light of the Doctrine of Descent, no longer as the ingeniously designed work of a Creator building up according to a definite purpose, but as the necessary consequence of active causes, which are inherent in the chemical combination of matter itself, and in its physical properties.
In fact, we can most positively assert, and I shall justify this assertion in the course of these pages, that by the Doctrine of Filiation, or Descent, we are enabled for the first time to reduce all organic phenomena to a single law, and to discover a single active cause for the infinitely intricate mechanism of the whole of this rich world of phenomena. In this respect, Darwin’s theory stands quite on a level with Newton’s Theory of Gravitation; indeed, it even rises higher than Newton’s theory!
The grounds of explanation are equally simple in the two theories. In explaining this most intricate world of phenomena, Darwin does not make use of new or hitherto unknown properties of matter, nor does he, as one might suppose, make use of discoveries of new combinations of matter or of new forces of organization; but it is simply by extremely ingenious combination, by the synthetic comprehension, and by the thoughtful comparison of a number of well-known facts, that Darwin has solved the “holy mystery” of the living world of forms. The consideration of the interchanging relations which exist between two general properties of organisms, viz., Inheritance and Adaptation, is what has here been of the first importance. Merely by considering the relations between these two vital actions or physiological functions of organisms, also further by considering the reciprocal interaction which all animals and plants, living in one and the same place, necessarily exert on one another—solely by the correct estimate of these simple facts, and by skilfully combining them, Darwin has succeeded in finding the true active causes (causæ efficientes) of the immensely intricate world of forms in organic nature.