founded, are in no wise disturbed by the establishment of any such scientific theorem. . The theological question is left just where it was before. We are still at perfect liberty to maintain that it is the direct action of Deity which is manifested in the planetary movements; having done nothing more with our Newtonian hypothesis than to construct a happy formula for expressing the mode or order of the manifestation. We may have learned something new concerning the manner of Divine action; we certainly have not "substituted" any other kind of action for it. And what is thus obvious in this simple astronomical example is equally true in principle in every case whatever in which one set of phenomena is interpreted by comparison with another set. In no case whatever can science use the words "force" "or "( cause except as metaphorically descriptive of some observed or observable sequence of phenomena. And consequently at no imaginable future time, so long as the essential conditions of human thinking are maintained, can science even attempt to substitute the action of any other power for the direct action of Deity. Darwinism may convince us that the existence of highly complicated organisms is the result of an infinitely diversified aggregate of circumstances so minute as severally to seem trivial or accidental; yet the consistent theist will always occupy an impregnable position in maintaining that the entire series in each and every one of its incidents is an immediate manifestation of the creative action of God. From an obverse point of view it might be argued that since a philosophical theism must regard Divine power as the immediate source of all phenomena alike, therefore science cannot properly explain any particular group of phenomena by a direct reference to the action of Deity. Such a reference is not an explanation, since it adds nothing to our previous knowledge either of the phenomena or of the manner of Divine action. The business of science is simply to ascertain in what manner phenomena coexist with each other or follow each other, and the only kind of explanation with which it can properly deal is that which refers one set of phenomena to another set. In pursuing this its legitimate business science does not trench on the province of theology in any way, and there is no conceivable occasion for any conflict between the two. From this and the previous considerations taken together it follows not only that such explanations as are contained in the Newtonian and Darwinian theories are entirely consistent with theism, but also that they are the only kind of explanations with which science can properly concern itself at all. To say that complex organisms were directly created by the Deity is to make an assertion which, however true in a theistic sense, is utterly barren. It is of no profit to theism, which must be taken for granted before the assertion can be made; and it is of no profit to science, which must still ask its question, "How?" Setting aside, then, the theological criticism as irrelevant to the question really at stake, the Darwinian theory, like the Newtonian, remains to be tested by strictly scientific considerations. In the more recent instance, as in the earlier, the relevant question is how far the course of events as sketched by the hypothesis agrees with the observed phenomena of nature. But in the directness with which this question can be answered there is great difference between the two theories. The Newtonian hypothesis asserted the existence of a general physical property of matter, and could therefore be tested by a single crucial instance, such as was afforded by the simple case of the planetary motions. Kepler's three laws comprised in succinct form a very complete description of the movements of the planets, and when it was shown that these movements were just such as must occur according to the theory of gravitation, the theory was rightly regarded as verified. Further confirmatory instances could but repeat the same lesson, as when the irregularities of movement, due to the attractions exercised by the various planets upon each other, were likewise seen to conform strictly to the hypothesis. Nor was any alteration or enlargement of the original theory required in order to obtain the supreme triumph of verified prediction, as when Clairaut foretold the precise amount of delay in the reappearance of Halley's comet caused by the interfering attractions of Jupiter and Saturn, or as when Leverrier and Adams discovered the existence of Neptune through its effects upon the motions of Uranus. In all these cases the physical principle involved was simple, and admitted of precise mathematical treatment; and it is owing to this that the law of gravitation has become the most illustrious example which the history of science can furnish of a completely verified hypothesis. To look for similar conciseness of verification in the case of the Darwinian theory would be to mistake entirely the conditions under which scientific evidence can be procured. To estimate properly the value of any hypothesis it is necessary that we should know what kind and degree of proof to expect; and in the present case we must not look for a demonstration that shall be direct and simple. Instead of a universal property of matter, so conspicuous as to be recognized at once by the inspection of a few striking instances, we have in the theory of natural selection to deal with a very complex process working results of endless diversity throughout the organic world, and often masked in its action by accompanying processes, some of which we can detect without being able to estimate their relative potency, while others no doubt have thus far escaped our attention altogether. Accordingly, while we may consider it as certain that natural selection is capable of working specific changes in organisms, we may at the same time find it impossible to give a complete account of the origin of any one particular species through natural selection, because we can never be sure that we have taken due notice of all the innumerable concrete circumstances involved in such an event. The theory, therefore, cannot be adequately tested by any single striking instance, but must depend for its support on the cumulative evidence afforded by its general harmony with the processes of organic nature. If we consider the Darwinian theory as a whole, it must be admitted that such cumulative evidence has already been brought forward in sufficient quantity to amount to a satisfactory demonstration. The convergence of proofs is too persistent and unmistakable to allow of any alternative hypothesis being put in the field. But in exhibiting this, it is desirable that there should be no confusion of thought as to the full import of the Darwinian theory. Mr. Mivart's way of describing that theory as an attempt to account for the origin of all the various forms of life through the operation of natural selection alone, is a gross misrepresentation. Mr. Darwin has never urged his hypothesis in this limited. shape. The essential theorems of Darwinism are, first, that forms of life now widely unlike have been produced from a common original through the accumulated inheritance of minute individual modifications; and, secondly, that such modifications have been ac " cumulated mainly, or in great part, through the selection of individuals best fitted to survive and transmit their peculiarities to their offspring. But that this survival of the fittest individuals has been the sole agency concerned in bringing about the present wondrous variety of living beings, Mr. Darwin has nowhere asserted or implied, having even in the earliest edition of his great work explicitly pointed out certain other agencies as involved in the complex result. Yet other agencies, hitherto unsuspected, may be discovered in the future; but such discoveries, however far they may go in supplementing the Darwinian theory, can only strengthen its central position as regards the rise of specific differences through gradual modifications. That natural selection is a true cause, and one capable of accumulating variations to an indefinite extent, is now held to be beyond question. The wonders wrought by artificial selection in the breeding of domestic animals and cultivated plants are such that one might well have attributed great results to the exercise of a similar selection by Nature through countless ages, could any such process be detected. Few, however, save those instructed naturalists who have frequent occasion to ponder the subject, are aware what a tremendous reality natural selection is. As I have elsewhere observed, "a single codfish has been known to lay six million eggs within a year. If these eggs were all to become adult codfishes, and the multiplication were to continue at this rate for three or four years, the ocean would not afford room for the species. Yet we have no reason to suppose that the race of codfishes is actually increasing in numbers to any notable extent. With the codfish, as with animal species in general, the numbers during many successive generations oscillate about a point which is fixed, or moves but slowly forward or backward. Instead of a geometrical increase with a ratio of six millions, there is practically no marked increase at all. Now this implies that out of the six million embryo codfish a sufficient number will survive to replace their two parents, and to replace a certain small proportion of those contemporary codfishes who leave no progeny. Perhaps a dozen may suffice for this, perhaps a hundred. The rest of the six million must die." * The amount of destruction is not so great as * Outlines of Cosmic Philosophy, Vol. II. p. 12. this in all parts of the animal kingdom. Among the higher birds and mammals the preservation of the individual bears a very much higher ratio to the preservation of the race. But with the immense classes of fishes, insects, and crustaceans, as well as the sub-kingdom of molluscs, which taken together make up by far the greater portion of the animal world, the destruction continually going on is probably not less than that which is described in the example cited. Even if we were to take account only of the individuals which survive the embryo or larva state, but do not succeed in leaving offspring behind them, the cases of destruction would still bear an enormous ratio to the cases of preservation. But in maintaining the characteristics of a race only those individuals can be counted who produce offspring. It is obvious then that each species of organisms, as we know it, consists only of a few favored individuals selected out of countless multitudes who have been tried and rejected as unworthy to live. No selection that is exercised by man compares in rigor with this. It is somewhat as if a breeder of race-horses were to choose, with infallible accuracy of judgment, the two or three fleetest out of each hundred thousand, destroying all the rest that the high standard of the breed might run no possible risk of deterioration. In such a rigorous competition as this, no individual peculiarity can be so slight that we are entitled to regard it as unimportant. No peculiarity is really slight that enables its possessor to survive until he transmits it to posterity. In view of all this we see how misleading it is to describe natural selection (as Mr. Mivart does) as a process which operates only occasionally upon variations assumed to be fortuitous. We see that natural selection, like a power that slumbers not nor sleeps, is ever preserving the stability of species by seizing all individual peculiarities that oscillate within narrow limits on either side of the mean that is most advantageous to the species, while cutting off all such peculiarities as transgress these limits. Domesticated animals, protected from the exigencies of wild life, often exhibit great varieties in coloring, while wild animals of the same genus or species are monotonously colored, because only one kind of coloring will aid them in catching prey or eluding enemies, and all the variations are killed out. Who can 'doubt that antelopes are so fleet, only because all but the fleetest individuals are sure to be NO. 254. VOL. CXXIV. · 7 |