Freedom in Science and Teaching, Ernst Haeckel, T. H. Huxley [people reading books .txt] 📗

This brings us to that question which, in the popular treatment of the theory of descent, is justly considered as its most important outcome and as the keystone of the evolutionist edifice--to the well-known proposition, "Man is descended from the Ape." While we simply ignore all the misrepresentation, distortion, and misinterpretation which this ape, or pithecoid hypothesis, has met with on all sides, we will only remark that this fundamental proposition, in the sense of our modern doctrine of evolution, can rationally have only this plain meaning: that the human species as a whole was long since developed from the order of apes, indeed actually from one (or perhaps more) long since extinct form of ape; the immediate progenitors of man in the long series of his vertebrate ancestry were apes or ape-like animals. Of course none of the now surviving species of apes is to be regarded as the unaltered posterity of that primeval parent-form. Virchow, however, understanding the "ape question" in this sense, answers it, as Bastian also does, with the most positive contradiction. "We cannot teach the doctrine that man is descended from apes or from any other animal, for we cannot regard it as a real acquisition of science" (p. 31). Although I myself, in direct opposition to this view, and in agreement with almost all my professional colleagues, look upon the descent of man from apes as one of the surest of phylogenetic hypotheses, I will here expressly admit that the relative certainty of this, as of all other historical hypotheses of descent, is not comparable with the absolute certainty of the general theory of descent. It is now ten years since I first explicitly stated (in my "Natural History of Creation," vol. ii. p. 358): "The pedigree of the human race, like that of every animal or plant, remains in detail a more or less approximate general hypothesis. This, however, in no way affects the application of the theory of descent to man. In this, as in all researches into the derivation of our organism, we must distinguish between the general theory of descent and the specific hypothesis of descent. The general theory of descent claims full and permanent value, because it is inductively based on the whole range of common biological phenomena and on their internal causal connection. Each special hypothesis of descent, on the other hand, is conditional as to its specific value on the existing state of our biological information, and on the extent of those objective empirical grounds on which we deductively found the hypothesis, by our subjective inferences." And I must here emphatically add that I have on every opportunity repeated that reservation, and have always insisted on the difference which exists between the absolute certainty of transmutation in general and the relative certainty of each individual specific pedigree. So that when Semper and others of my opponents assert that I teach my specific genealogies as "infallible dogmas," it is simply false. I have, on the contrary, pointed out on all occasions that I regard them only as heuristic or provisional hypotheses, and as a means of investigating the actual relations of cognate races of organic forms more and more approximately.

Since the conception of the natural animal system as a hypothetical genealogical tree, and the phylogenetic interpretation of morphological affinity which that conception involves, afford in fact the only rational interpretation of that affinity in general, my first genealogical attempts soon found many imitators, and at the present time numerous industrious labourers in the different departments of systematic zoology are endeavouring to find in the construction of such hypothetical genealogies the shortest and completest expression of the modern conception of structural affinity. If Virchow had not been as ignorant of the true significance and method of systematic morphology as he is of its progress and scientific contents, he must certainly have known this, and then he would surely have withheld his mockery of all these grave phylogenetic studies as "personal crotchets" and worthless dreams.

What mighty strides towards a mechanical morphology we have made by this phylogenetic working out of the system, and how much light and life it has at once thrown into the system that before was dead and cold, can only be known to those who have long and deeply studied specific systematisation and the grouping of species; Virchow has not the remotest suspicion of it. Moreover, these attempts have now proceeded so far, that a large proportion of the phylogenetic hypotheses are regarded as very nearly certain, and can hardly undergo any further essential modifications; while the greater number of them are still in an unfixed state, and one systematist tries to improve them in this direction, and another in that.

The following phylogenetic hypotheses are held to be almost certain:----The descent of many-celled animals from single-celled, of the Medusæ from the hydroid Polyps, of the jointed from the unjointed worms, of the sucking from the gnawing insects, of amphibious animals from fishes, of birds from reptiles, of the placental mammalia from the marsupials, and so forth. I personally consider the descent of man from the apes as equally certain; nay, I regard this most important and pregnant genealogical hypothesis as one of those which, up to the present time, rest on the best empirical basis.

Huxley, in particular, fifteen years ago, in his celebrated "Man's Place in Nature," 1863, so admirably proved the undoubted "descent of man from apes," and so clearly discussed all the relations that had to be taken into consideration, that very little was left to others to do. The result of his comparative morphological investigations is contained in this proposition----" If we take up a system of organs, be it which we will, the comparison of its modifications throughout the series of apes leads us to the same conclusion: that in every single visible character man differs less from the higher apes than these do from the lower members of the same order." It is therefore impossible for any objective zoologist, according to the principles of comparative systematisation, to ascribe to man any other place in the animal world than in the order of apes; and it is quite immaterial whether we designate this individual group as the Order of Apes, or, with Linnæus, as the Primates. For the phylogenetic construction of the system, the common descent of man and of apes from one common parent-form, necessarily follows from this inevitable grouping, and on this proposition only all the general inferences of the "ape-hypothesis" depend. As to what that common parent-form of men and apes may have been, very different views might probably be brought on opposite sides; but any one who knows the collected facts that bear upon the matter, and estimates them impartially, must, in conclusion, arrive at the certain conviction that that hypothetical and long-since extinct parent-form can only have been genuine apes; that is to say, of the placental mammalian type, such as when we see them now living before our eyes we unhesitatingly class, on the ground of their zoological characters, as true apes, in the order of Apes or Primates.

In this, and all other sound phylogenetic hypotheses, we may most easily attain to a conviction of their truth by taking into consideration and comparison the other possible hypotheses. But in fact no single opponent of the ape-hypothesis has been able to combat it with any other phylogenetic hypothesis that has the faintest glimmer of probability. Not one opponent has suggested, or can suggest, any other animal form that can serve as our nearest ancestor than the ape. No one has ever reproached me by saying that Mother Nature has endowed me with too little imagination; on the contrary, I am often accused of having a superfluity of that gift of the gods; but I have often and repeatedly exerted my imagination to picture to myself any known or unknown animal-form as the nearest parent-form to man in the place of the apes, and have always found myself under the necessity of falling back upon the stock of apes. Let me conceive of the outward conformation and the internal structure of the nearest mammalian ancestors of men as I will, I am always forced to acknowledge that this hypothetical parent-form ranges under the zoologically-conceived order of apes, and cannot possibly be separated from the Simiadoe or Primates. If, in spite of this, any one chooses, out of a "personal crotchet," to accept some other series of unknown animal ancestors of man that have nothing to do with apes, that is but a mere empty hypothesis floating in the air. Our ape-hypothesis, on the other hand, is objectively and thoroughly proved by the essential agreement of the internal bodily structure of man and of apes, and by the identity of their embryonic development, as I have fully shown in my "Evolution of Man" (chaps. xix. and xxvi.) The mode and manner in which he here puts palæontology in the foreground, and throws on the theory of descent the task of producing an unbroken gradation of fossil transitional forms between the apes and man, is very indicative of Virchow's ignorance of this zoological question--in which I, as a professional zoologist, must decisively declare his incompetence. The reasons why such a solution of the problem is not to be expected, the extraordinary imperfection of the palæontological record, the natural impediments to the palæontological evidence of the genealogical table, have been so lucidly unfolded by Darwin himself (chaps. ix. and x. of the "Origin of Species") that I am obliged once more to come to the conclusion that Virchow has never read it with any attention.

Besides, long before Darwin, the gifted Lyell, the great originator of modern geology, showed clearly and convincingly how, for many reasons, the greater part of the fossil series must remain most imperfect, and these reasons were at a later period so often and so fully discussed (by myself among others, in chap. xv. of the "History of Creation," vol. ii. pp. 24-32) that it is wholly superfluous once more and in this place to state these well-known and time-worn questions. It only shows how little Virchow was acquainted with geology and palæontology, and what a limited judgment he can form of these historical causal relations.

No attack in Virchow's Munich address surprised me so much, and none so plainly betrayed the subversion of his most important scientific views, as that which he directed against my observations on psychology and cellular physiology. A mystic dualism in his fundamental views is here revealed, which stands in the sharpest contrast to the mechanical monism formerly upheld by the famous pathologist of Würzburg.

In my Munich discourse (p. 12), I had alluded to the "grand and fruitful application which Virchow had made, in his system of cellular pathology, of the cell-theory to the general province of theoretic medicine;" and as a logical amplification of that idea, I asserted emphatically that we must ascribe an independent soul-life to every individual organic cell. "This conception is validly proved by the study of infusoria, amoebæ, and other one-celled organisms; for, in these individual, isolated, living cells we find the same manifestations of soul-life--feelings, and ideas (mental images), will and motion, as is