Volume II Part 20 (1/2)

Now we shall find that these indispensable preliminary conditions are, unfortunately, by no means fulfilled by the majority of naturalists of the present day. The immense amount of empirical facts with which the gigantic advances of modern natural science have recently made us acquainted has led to a prevailing inclination for the special study of single phenomena and of small and narrow domains. This causes the knowledge of other paths, and especially of Nature as a great comprehensive whole, to be in most cases completely neglected. Every one with sound eyes and a microscope, together with industry and patience for study, can in our day attain a certain degree of celebrity by microscopic ”discoveries,” without, however, deserving the name of a naturalist. This name is deserved only by him who not merely strives to _know_ the individual phenomena, but who also seeks to _discover_ their causal connection. Even in our own day, most palaeontologists examine and describe fossils without knowing the most important facts of embryology.

Embryologists, on the other hand, follow the history of development of a particular organic individual, without having an idea of the palaeontological history of the whole tribe, of which fossils are the records. And yet these two branches of the organic history of development-ontogeny, or the history of the individual, and phylogeny, or the history of the tribe-stand in the closest causal connection, and the one cannot be understood without the other. The same may be said of the systematic and the anatomical part of Biology. There are even now, in zoology and botany, many systematic naturalists who work with the erroneous idea that it is possible to construct a natural system of animals and plants simply by a careful examination of the external and readily accessible forms of bodies, without a deeper knowledge of their internal structure. On the other hand, there are anatomists and histologists who think it possible to obtain a true knowledge of animal and vegetable bodies merely by a most careful examination of the inner structure of the body of some individual species, without the comparative examination of the bodily form of all kindred organisms. And yet here, as everywhere, the internal and external factors, to wit, Inheritance and Adaptation, stand in the closest mutual relation, and the individual can never be thoroughly understood without a comparison of it with the whole of which it is a part. To those one-sided specialists we should like in Goethe's words to say:-

We must, contemplating Nature, Part as Whole, give equal heed to: Nought is inward, nought is outward, For the inner is the outer.[6]

And again:-

Nature has neither kernel nor sh.e.l.l, It is she that is All and All at once.[7]

What is even more detrimental to the general understanding of nature as a whole than this one-sided tendency, is _the want of a philosophical culture_, and this applies to most of the naturalists of the present day. The various errors of the earlier speculative nature-philosophy made during the first thirty years of our century, have brought the whole of philosophy into such bad repute with the exact empirical naturalists, that they live in the strange delusion that it is possible to erect the edifice of natural science out of mere facts, without their philosophic connection; in short, out of mere knowledge, without the understanding of it. But as a purely speculative and absolutely philosophical system, which does not concern itself with the indispensable foundation of empirical facts, becomes a castle in the air, which the first real experiment throws to the winds; so, on the other hand, a purely empirical system, constructed of nothing but facts, remains a disorderly heap of stones, which will never deserve the name of an edifice. Bare facts established by experience are nothing but rude stones, and without their thoughtful valuation, without their philosophic connection, no science can be established. As I have already tried to impress upon my reader, the _strong edifice of true monistic science_, or what is the same thing, the _Science of Nature, exists only by the closest interaction, and the reciprocal penetration of philosophy and empirical knowledge_.

This lamentable estrangement between science and philosophy, and the rude empiricism which is now-a-days unfortunately praised by most naturalists as ”exact science,” have given rise to those strange freaks of the understanding, to those gross insults against elementary logic, and to that incapacity for forming the simplest conclusions which one may meet with any day in all branches of science, but especially in zoology and botany. It is here that the neglect of a philosophical culture and training of the mind, directly avenges itself most painfully. It is not to be wondered at that the deep inner truth of the Theory of Descent remains a sealed book to those rude empiricists. As the common proverb justly says: they cannot see the wood for the trees.

It is only by a more general philosophical study, and especially by a more strictly logical training of the mind, that this sad state of things can be remedied. (Compare Gen. Morph. i. 63; ii. p. 447.)

If we rightly consider this circ.u.mstance, and if we further reflect upon it in connection with the empirical foundation of the philosophical theory of development, we shall at once see how we are placed respecting the oft-demanded _proofs of the theory of descent_. The more the doctrine of filiation has of late years made way for itself, and the more all thoughtful, younger naturalists, and all truly biologically-educated philosophers have become convinced of its inner truth and absolute necessity, the louder have its opponents called for actual proofs. The same persons who, shortly after the publication of Darwin's work, declared it to be ”a groundless, fantastic system,” an ”arbitrary speculation,” an ”ingenious dream,” now kindly condescend to declare that the theory of descent certainly is a scientific ”_hypothesis_,” but that it still requires to be ”_proved_.” When these remarks are made by persons who do not possess the requisite empirico-philosophical culture, nor the necessary knowledge in comparative anatomy, embryology, and palaeontology, we cannot be much offended, and we refer them to the study of those sciences. But when similar remarks are made by acknowledged specialists, by teachers of zoology and botany, who certainly ought to possess a general insight into the whole domain of their science, or who are actually familiar with the facts of those scientific domains, then we are really at a loss what to say. Those who are not satisfied with the treasures of our present empirical knowledge of nature as a basis on which to establish the Theory of Descent, will not be convinced by any other facts which may hereafter be discovered; for we can conceive no circ.u.mstances which would furnish stronger or a more complete testimony to the truth of the doctrine of filiation than is even now seen, for example, in the well-known facts of comparative anatomy and ontogeny. I must here again direct attention to the fact, _that all the great and general laws, and all the comprehensive series of phenomena of the most different domains of biology can only be explained and understood by the Theory of Development_ (and especially by its biological part, the Theory of Descent), and that without it they remain completely inexplicable and incomprehensible. _The internal causal connection_ between them all proves the Theory of Descent to be the greatest _inductive law_ of Biology.

Before concluding, I will once more name all those series of inductions, all those general laws of Biology, upon which this comprehensive law of development is firmly based.

(1.) _The palaeontological history of the development of organisms_, the gradual appearance and the historical succession of the different species and groups of species, the empirical laws of the palaeontological change of species, as furnished to us by the science of fossils, and more especially the _progressive differentiation and perfecting_ of animal and vegetable groups in the successive periods of the earth's history.

(2.) _The individual history of development of organisms_, embryology and metamorphology, the gradual changes in the slow development of the body and its particular organs, especially _the progressive differentiation and perfecting_ of the organs and parts of the body in the successive periods of the individual development.

(3.) _The inner causal connection between ontogeny and phylogeny_, the parallelism between the individual history of the development of organisms, and the palaeontological history of the development of their ancestors, a connection which is actually established by the laws of _Inheritance_ and _Adaptation_, and which may be summed up in the words: ontogeny, according to the laws of inheritance and adaptation, repeats in its large features the outlines of phylogeny.

(4.) _The comparative anatomy of organisms_, the proof of the essential agreement of the inner structure of kindred organisms, in spite even of the greatest difference of external form in the various species; their explanation by the causal dependence of the internal agreement of the structure on _Inheritance_, the external dissimilarity of the bodily form on _Adaptation_.

(5.) _The inner causal connection between comparative anatomy and the history of development_, the harmonious agreement between the laws of the gradual development, _the progressive differentiation and perfecting_, as they may be seen in comparative anatomy on the one hand, in ontogeny and palaeontology on the other.

(6.) _Dysteleology, or the theory of purposelessness_, the name I have given to the _science of rudimentary organs_, of suppressed and degenerated, aimless and inactive, parts of the body; one of the most important and most interesting branches of comparative anatomy, which, when rightly estimated, is alone sufficient to refute the fundamental error of the teleological and dualistic conception of Nature, and to serve as the foundation of the mechanical and monistic conception of the universe.

(7.) _The natural system of organisms_, the natural grouping of all the different forms of Animals, Plants, and Protista into numerous smaller or larger groups, arranged beside and above one another; the kindred connection of species, genera, families, orders, cla.s.ses, tribes, etc., more especially, however, the _arboriform branching character of the natural system_, which is the spontaneous result of a natural arrangement and cla.s.sification of all these graduated groups or categories. The result attained in attempting to exhibit the relations.h.i.+ps of the mere forms of organisms by a tabular cla.s.sification is only explicable when regarded as the expression of their actual _blood relations.h.i.+p_; _the tree shape of the natural system_ can only be understood as the actual _pedigree of the organisms_.

(8.) _The chorology of organisms_, the science of the local distribution of organic species, of their _geographical_ and _topographical dispersion over the surface of the earth_, over the heights of mountains and in the depths of the ocean, but especially the important phenomenon that every species of organism proceeds from a so-called ”_centre of creation_” (more correctly a ”_primaeval home_” or ”_centre of distribution_”); that is, from a single locality, where it originated but once, and whence it spread.

(9.) _The cology of organisms_, the knowledge of the sum of the _relations of organisms to the surrounding outer world_, to organic and inorganic conditions of existence; the so-called ”_economy of nature_,”

the correlations between all organisms living together in one and the same locality, their adaptation to their surroundings, their modification in the struggle for existence, especially the circ.u.mstances of parasitism, etc. It is just these phenomena in ”the economy of nature” which the unscientific, on a superficial consideration, are wont to regard as the wise arrangements of a Creator acting for a definite purpose, but which on a more attentive examination show themselves to be the necessary results of mechanical causes.

(10.) _The unity of Biology as a whole_, the deep inner connection existing between all the phenomena named and all the other phenomena belonging to zoology, protistics, and botany, and which are simply and naturally explained by a single common principle. This principle can be no other than the common derivation of all the specifically different organisms from a single, or from several absolutely simple, primary forms like the Monera, which possess no organs. The Theory of Descent, by a.s.suming this common derivation, throws a clear light upon these individual series of phenomena, as well as upon their totality, without which their deeper causal connection would remain completely incomprehensible to us. The opponents of the Theory of Descent can in no way explain any single one of these series of phenomena or their deeper connection with one another. So long as they are unable to do this, _the Theory of Descent remains the one adequate biological theory_.

We should, on account of the grand proofs just enumerated, have to adopt Lamarck's Theory of Descent for the explanation of biological phenomena, even if we did not possess Darwin's Theory of Selection. The one is so completely and _directly proved_ by the other, and established by mechanical causes, that there remains nothing to be desired. The laws of _Inheritance_ and _Adaptation_ are universally acknowledged _physiological_ facts, the former traceable to _propagation_, the latter to the _nutrition_ of organisms. On the other hand, the _struggle for existence_ is a _biological_ fact, which with mathematical necessity follows from the general disproportion between the average number of organic individuals and the numerical excess of their germs. But as Adaptation and Inheritance in the struggle for life are in continual interaction, it inevitably follows that _natural selection_, which everywhere influences and continually changes organic species, must, by making use of _divergence of character_, produce new species. Its influence is further especially favoured by the active and pa.s.sive _migrations_ of organisms, which go on everywhere. If we give these circ.u.mstances due consideration, the continual and gradual modification or trans.m.u.tation of organic species will appear as a biological process, which must, according to causal law, of _necessity_ follow from the actual nature of organisms and their mutual correlations.

That even the _origin of man_ must be explained by this general organic process of trans.m.u.tation, and that it is simply as well as naturally explained by it, has, I believe, been sufficiently proved in my last chapter but one. I cannot, however, avoid here once more directing attention to the inseparable connection between this so-called ”theory of apes,” or ”pithecoid theory,” and the whole Theory of Descent. If the latter is the greatest _inductive law_ of biology, then it of necessity follows that the former is its most important _deductive law_. They stand and fall together. As all depends upon a right understanding of this proposition, which in my opinion is very important, and which I have therefore several times brought before the reader, I may be allowed to explain it here by an example.

In all mammals known to us the centre of the nervous system is the spinal marrow and the brain, and the centre of the vascular system is a quadrupal heart, consisting of two princ.i.p.al chambers and two ante-chambers. From this we draw the general inductive conclusion that all mammals, without exception, those extinct, together with all those living species as yet unknown to us, as well as the species which we have examined, possess a like organization, a like heart, brain, and spinal marrow. Now if, as still happens every year, there be discovered in any part of the earth a new species of mammal, a new species of marsupial, or a new species of deer, or a new species of ape, every zoologist knows with certainty at once, without having examined its inner structure, that this species must possess a quadruple heart, a brain and spinal marrow, like all other mammals. Not a single naturalist would ever think of supposing that the central nervous system of this new species of mammal could possibly consist of a ventral cord with an sophageal collar as in the insects, or of scattered pairs of knots as in the molluscs, or that its heart could be many-chambered as in flies, or one-chambered as in the tunicates. This completely certain and safe conclusion, although it is not based upon any direct experience, is a _deductive conclusion_. In the same way, as I have shown in a previous chapter, Goethe, from the comparative anatomy of mammals, established the general inductive conclusion that they all possess a mid jawbone, and afterwards drew from it the special deductive conclusion that man, who in all other respects does not essentially differ from other mammals, must also possess a like mid jawbone. He maintained this conclusion without having actually seen the human mid jawbone, and only proved its existence subsequently by actual observation (vol. i. p. 84).

The process of _induction_ is a logical system of forming conclusions _from the special to the general_, by which we advance from many individual experiences to a general law; _deduction_, on the other hand, draws a conclusion _from the general to the special_, from a general law of nature to an individual case. Thus the _Theory of Descent_ is, without doubt, a great _inductive law_, empirically based upon all the biological experience cited above; the pithecoid theory, on the other hand, which a.s.serts that man has developed out of lower, and in the first place out of ape-like mammals, is a _deductive law_ inseparably connected with the general inductive law.

The pedigree of the human race, the approximate outlines of which I gave in the last chapter but one, of course remains in detail (like all the pedigrees of animals and plants previously discussed) a more or less approximate general hypothesis. This however does not affect the application of the theory of descent to man. Here, as in all investigations on the derivation of organisms, one must clearly distinguish between the general _theory_ of descent and the special _hypotheses_ of descent. The general _theory_ of descent claims full and lasting value, because it is an inductive law, based upon all the whole series of biological phenomena and their inner causal connection. Every special _hypothesis_ of descent, on the other hand, has its special value determined by the existing condition of our biological knowledge, and by the extent of the objective empirical basis upon which we deductively establish this particular hypothesis. Hence, all the individual attempts to obtain a knowledge of the pedigree of any one group of organisms possesses but a temporary and conditional value, and any special hypothesis relating to it will become the more and more perfect the greater the advance we make in the comparative anatomy, ontogeny, and palaeontology of the group in question. The more, however, we enter into genealogical details, and the further we trace the separate off-shoots and branches of the pedigree, the more uncertain and subjective becomes our special _hypothesis_ of descent on account of the incompleteness of our empirical basis. This however does no injury to the general _theory_ of descent, which remains as the indispensable foundation for really profound apprehension of biological phenomena.

Accordingly, there can be no doubt that we can and must, with full a.s.surance, regard the derivation of man-in the first place, from ape-like forms; farther back, from lower mammals, and thus continually farther back to lower stages of the vertebrata down to their lowest invertebrate roots, nay, even down to a simple plastid-as a general _theory_. On the other hand, the special tracing of the human pedigree, the closer definition of the animal forms known to us, which either actually belong to the ancestors of man, or at least stand in very close blood relations.h.i.+p to them, will always remain a more or less approximate _hypothesis_ of descent, all the more in danger of deviating from the real pedigree the nearer it endeavours to approach it by searching for the individual ancestral forms. This state of things results from the immense gaps in our palaeontological knowledge, which can, under no circ.u.mstances, ever attain to even an approximate completeness.

A thoughtful consideration of this important circ.u.mstance at once furnishes the answer to a question which is commonly raised in discussing this subject, namely, the question of scientific _proofs for the animal origin of the human race_. Not only the opponents of the Theory of Descent, but even many of its adherents who are wanting in the requisite philosophical culture, look too much for ”signs” and for special empirical advances in the science of nature. They await the sudden discovery of a human race with tails, or of a talking species of ape, or of other living or fossil transition forms between man and the ape, which shall fill the already narrow chasm between the two, and thus empirically ”prove” the derivation of man from apes. Such special manifestations, were they ever so convincing and conclusive, would not furnish the proof desired. Unthinking persons, or those unacquainted with the series of biological phenomena, would still be able to maintain the objections to those special testimonies which they now maintain against our theory.