My quarrel with the conclusion, like my quarrel with the premiss, is due to its universality. By saying in the premiss that all incipient organs are necessarily useless at the time of their inception, these writers admit of being controverted by fact; and by saying in the conclusion that, if all incipient organs are useless, it necessarily follows that in no case can natural selection have been the cause of building up an organ until it becomes useful, they admit of being controverted by logic. For, even if the premiss were true in fact—namely, that all incipient organs are useless at the time of their inception,—it would not necessarily follow that in no case could natural selection build up a useless structure into a useful one; because, although it is true that in no case can natural selection do this by acting on a useless structure directly, it may do so by acting on the useless structure indirectly, through its direct action on some other part of the organism with which the useless structure happens to be correlated. Moreover, as I believe, and will subsequently endeavour to prove, there is abundant evidence to show that incipient characters are often developed to a large extent by causes other than natural selection (or apart from any reference to utility), with the result that some of them thus happen to become of use, when, of course, the supposed difficulty is at an end.
But although it is thus easy to dispose of both the propositions in question, on account of their universality, stated more carefully they would require, as I have said, more careful consideration. Thus, if it had been said that some incipient organs are presumably useless at the time of their inception, and that in some of these cases it is difficult, or impossible, to conceive how the principle of correlation, or any other principle hitherto suggested, can apply—then the question would have been raised from the sphere of logical discussion to that of biological fact. And the new question thus raised would have to be debated, no longer on the ground of general or abstract principles, but on that of special or concrete cases. Now until within the last year or two it has not been easy to find such a special or concrete case—that is to say, a case which can be pointed to as apparently excluding the possibility of natural selection having had anything to do with the genesis of an unquestionably adaptive structure. But eventually such a case has arisen, and the Duke of Argyll has not been slow in perceiving its importance. This case is the electric organ in the tail of the skate. No sooner had Professor Cossar Ewart published an abstract of his first paper on this subject, than the Duke seized upon it as a case for which, as he said, he had long been waiting—namely, the case of an adaptive organ the genesis of which could not possibly be attributed to natural selection, and must therefore be attributed to supernatural design. Now, I do not deny that he is here in possession of an admirable case—a case, indeed, so admirable that it almost seems to have been specially designed for the discomfiture of Darwinians. Therefore, in order to do it full justice, I will show that it is even more formidable than the Duke of Argyll has represented.
Electric organs are known to occur in several widely different kinds of fish—such as the Gymnotus and Torpedo. Wherever these organs do occur, they perform the function of electric batteries in storing and discharging electricity in the form of more or less powerful shocks. Here, then, we have a function which is of obvious use to the fish for purposes both of offence and defence. These organs are everywhere composed of a transformation of muscular, together with an enormous development of nervous tissue; but inasmuch as they occupy different positions, and are also in other respects dissimilar in the different zoological groups of fishes where they occur, no difficulty can be alleged as to these analogous organs being likewise homologous in different divisions of the aquatic vertebrata.
Now, in the particular case of the skate, the organ is situated in the tail, where it is of a spindle-like form, measuring, in a large fish, about two feet in length by about an inch in diameter at the middle of the spindle. Although its structure is throughout as complex and perfect as that of the electric organ in Gymnotus or Torpedo, its smaller size does not admit of its generating a sufficient amount of electricity to yield a discharge that can be felt by the hand. Nevertheless, that it does discharge under suitable stimulation has been proved by Professor Burdon Sanderson by means of a telephone; for he found that every time he stimulated the animal its electrical discharge was rendered audible by the telephone. Here, then, the difficulty arises. For of what conceivable use is such an organ to its possessor? We can scarcely suppose that any aquatic animal is more sensitive to electric shocks than is the human hand; and even if such were the case, a discharge of so feeble a kind taking place in water would be short-circuited in the immediate vicinity of the skate itself. So there can be no doubt that such weak discharges as the skate is able to deliver must be wholly imperceptible alike to prey and to enemies. Yet for the delivery of such discharges there is provided an organ of such high peculiarity and huge complexity, that, regarded as a piece of living mechanism, it deserves to rank as at once the most extremely specialized and the most highly elaborated structure in the whole animal kingdom. Thousands of separately formed elements are ranged in row after row, all electrically insulated one from another, and packed away into the smallest possible space, with the obvious end, or purpose, of conspiring together for the simultaneous delivery of an electric shock. Nevertheless, the shock when delivered is, as we have just seen, too slight to be of any conceivable use to the skate. Therefore it appears impossible to suggest how this astonishing structure—much more astonishing, in my opinion, than the human eye or the human hand—can ever have been begun, or afterwards developed, by means of natural selection. For if it be not even yet of any conceivable use to its possessor, clearly thus far survival of the fittest can have had nothing to do with its formation. On the other hand, seeing that electric organs when of larger size, as in the Gymnotus and Torpedo, are of obvious use to their possessors, the facts of the case, so far as the skate is concerned, assuredly do appear to sanction the doctrine of “prophetic germs.” The organ in the skate seems to be on its way towards becoming such an organ as we meet with in these other animals; and, therefore, unless we can show that it is now, and in all previous stages of its evolution has throughout been, of use to the skate, the facts do present a serious difficulty to the theory of natural selection, while they readily lend themselves to the interpretation of a disposing or fore-ordaining mind, which knows how to construct an electric battery by thus transforming muscular tissue into electric tissue, and is now actually in process of constructing such an apparatus for the prospective benefit of future creatures.
Should it be suggested that possibly the electric organ of the skate may be in process of degeneration, and therefore that it is now the practically functionless remnant of an organ which in the ancestors of the skate was of larger size and functional use—against so obvious a suggestion there lie the whole results of Professor Ewart’s investigations, which go to indicate that the organ is here not in a stage of degeneration, but of evolution. For instance, in Raia radiata, it does not begin to be formed out of the muscular tissue until some time after the animal has left the egg-capsule, and assumed all the normal proportions (though not yet the size) of the adult creature. The organ, therefore, is one of the very latest to appear in the ontogeny of R. radiata; and, moreover, it does not attain its full development (i. e. not merely growth, but transforming of muscular fibres into electrical elements) till the fish attains maturity. Read in the light of embryology, these facts prove, (1) that the electric organ of R. radiata must be one of the very latest products of the animal’s phylogeny; and, (2) that as yet, at all events, it has not begun to degenerate. But, if not, it must either be at a stand-still, or it must be in course of further evolution; and, whichever of these alternatives we adopt, the difficulty of accounting for its present condition remains. In this connexion also it is worth while to remark that the electric organ, even after it has attained its full development, continues its growth with the growth of the fish, and this in a much higher ratio, either than the tail alone, or the whole animal. Lastly, Prof. Burdon Sanderson finds that section for section the organ in the skate is as efficient as it is in Torpedo. It is evident that these facts also point to the skate’s organ being in course of phylogenetic evolution.
Fig. 118.—Raia radiata, representing the life size of the youngest individual in which muscle fibres have been found developing into electric cells.
