EVOLUTION 771 We may, no doubt, avoid this difficulty, in appearance at least, by assuming that all material processes down to the vibrations of the indivisible atoms are accompanied with a mode of feeling. This may, of course, be proposed as a properly scientific hypothesis, and as involving no metaphysical assumptions respecting the nature of atoms. The great difficulty here would be, how we are to conceive of modes of sensibility that do not enter into a collective consciousness, and which appear to lack all the character istics of our own conscious life. Even, however, if this huge difficulty of the genesis of mind is got over, there still remain limits to the explana tion effected by the doctrine of evolution. Thus, while it might be able to deduce all the processes of physical evolution from a few assumptions respecting primitive matter and its laws, it would have no such data for resolv ing all these steps in the mental process which result in a heterogeneous mode of feeling. How, for instance, is it to account ou general principles, and by a priori reason ing, for the differentiation of a vague tactual sensibility into what we know as sight and hearing sensibilities which underlie all our ordinary conceptions of the physical world] Here are manifestly set rigid limits to the explanation effected by the doctrine of evolution, the limits which J. S. Mill has laid down as those of all kinds of explanation of phenomena. The doctrine by no means helps us to resolve all laws of succession into one. The other limits set to the explanatory power of the modern doctrine have already been hinted at. Thus the doctrine sets out from a given point in time, at which it assumes a definite arrangement of material (and mental) elements to have obtained. " Of the beginning of the universe," says Professor Clifford, " we know nothing at all." Again, Professor J. Clerk Maxwell tells us 1 that we must from the first assume an infinite number of molecules exactly alike in their weight and rate of vibration ; and he distinctly argues against the supposition that this system of like elements can have been evolved. There is room then for the question, how this particular order of elements arose. And even if we go further back, and make with Mr Spencer the large assumption that these various classes of molecules have been evolved from perfectly homogeneous first elements, one may still ask for an explanation of this original homogeneity. In short, it is plain that every doctrine of evolution must assume some definite initial arrangement, which is supposed to contain the possibilities of the order which we find to be evolved, and no other possibility. Such being the limits set to the scope of explanation by the idea of evolution, the question arises whether these apparently permanent gaps in our scientific knowledge can be filled up by extra-scientific speculations. One may seek to show the need of such a metaphysical interpretation of evolution by n reference to the very nature of the doctrins. Asa scientific truth, it is simply the highest generalization respecting the order of phenomena in time, and as such makes no assumptions with regard to the ultimate nature of that matter, force, and mind, of which it speaks. What, it may be asked, are the realities corresponding to these terms, and how are we to conceive of their mutual relations ? Each of the supposed deficiencies in the doctrine of evolu tion just referred to leads us back to those various metaphy sical doctrines in which, as we have seen, the idea of evolu tion has usually clothed itself. In order to understand what Mr Martineau calls the whence as distinguished from the when, and to provide a substantial support for the 1 Discourse on Molecules. See also the very interesting section on the " Nature and Origin of Molecules," which concludes the work on the Tluory of Heat. thread of phenomenal events, it would seem as if we must fall back on some ultimate philosophic assumption respect ing the efficient principle in the process. With respect to metaphysical dualism, it must be said that it leaves us pretty much where we were. The corre lation of two distinct substances and their manifestations, in the way required by the doctrine of evolution (whether this correlation be universal or not), needs explanation as much as the correlation of the two sets of phenomena. On the other hand, materialism, spiritualism, and the so-called monism, have each their merits and their drawbacks as helps to the interpretation of evolution. If materialism recommends itself by assuming the fewest possible prin ciples, it is exposed to the objection that it bids us conceive a reality which is *,vholly distinct from mind. Further, it fails to give any intelligible account of the rise and pro gress of mental activity. Again, spiritualism assists us in accounting for the genesis of mind, and for the appearance of intelligent order in the world. Yet it is questionable whether this doctrine, assuming as it does some form of un conscious mind (whether as world-soul or as elements of feeling), is not beset with as many difficulties as it resolves. Further, it may be doubted whether the spiritualistic idea, in its common pantheistic form, has yet succeeded in render ing intelligible the fixed mechanical order which marks all stages of evolution. Finally, it may be allowed that the monistic doctrine of one reality with two faces does in appearance lift us over the difficulties which beset the materialistic and the spiritualistic interpretation of evolu tion. Only is it in truth anything more than a verbal simplification, and does it not rather leave us confined iu that dualism where science has to land us 1 It would thus seem that the doctrine of evolution has by no means as yet received its final philosophic character. No one of the metaphysical doctrines which are at our command is so plainly and completely adapted to transform it into a final doctrine of existence, that it must of necessity be accepted at once and by all. To this we must now add that to many minds this resort to a metaphysical principle as the support of the process .of evolution will not be held to be necessary. A positivist, who thinks that our knowledge of the universe must for ever be limited to phenomena, is at perfect liberty to accept the doctrine of evolution and to regard it as an ultimate expression for the order of the world. Nay more, the empirical idealist who may perhaps be defined as a posi tivist that has fully analysed his " phenomena " can accept and give a meaning to the doctrine of evolution as formu lating the order of sensations, actual and possible, of con scious minds. Mr Spencer somewhere says that, if idealism is true, evolution is a dream. Yet this assertion may be reasonably disputed. It may perhaps seem staggering to be told that evolution postulates vast periods of time in which there existed no mind to experience the sensations into which the world is on the idealistic hypothesis resolved. Yet this difficulty is only apparent, since past physical evolution stands for a projection, so to speak, of now existing minds, and for an order of sensations conceived as possible under other and imaginable circumstances. 2 To the empiri cal idealist physical evolution stands for an imagined order of perceptions in an indefinite number of minds, mental evolution for actual successions of feeling in many minds, and the transition from the one to the other means the suc cession of actual states of consciousness on possible or imagined states. The unity of the world-process arises from the ability of the individual mind, which now reflects 8 It may be added that the hypothesis of the uniform correlation of the physical and the mental enables us to assign an element of
actuality (mental life) to the remote ptriods here spoken of.