80 VARIATION Survival of fittest a vera causa. Uni- formi- tarian- ism in natural change. and (4) power of prediction, it seems difficult for the most sceptical of critics to avoid ranking it very high, while to those who regard it as triumphantly surviving this assay the "law of parsimony " appears to preclude the necessity of seeking any further explanation of evolution. 1 As no serious critic wholly denies the fact of a struggle for existence, nor even a certain preponderance among the survivors in any given area of those best fitted for the struggle, however much he may consider the importance of these facts to have been overstrained in certain direc tions, we are fairly entitled at the outset to regard natural selection, not only as provisionally superseding earlier attempts at solving the problems of geological and geo graphical distribution, but as adequately, it might almost seem finally, explaining them (see BIOLOGY, DISTRIBU TION). This claim at any rate must be allowed even by those who deny the importance of natural selection as a substantial factor in evolution in the other sub-sciences of physiology and morphology, and this not simply because it was as experts in distribution that Darwin and Wallace themselves arrived at their hypothesis, nor because all subsequent Avorkers in that field of science have adopted it, but because no valid objection, or even supplementary hypothesis, has ever, as regards this important department of science, been so much as proposed. The survival of the fittest, then, is unquestionably a vera causa, and one of no small importance in the study of nature (in fact, in undisputed possession of at least one entire field), as also in the study of social life, from which both Darwin and Wallace were directly inspired. 2 The importance of breed ing and artificial selection is also undisputed ; nor can some small scope for natural selection in the formation of varieties of wild races be denied even by the most grudging of critics who may be versed in the facts of natural history at all. But this amounts to admitting that natural selec tion, already the undisputed explanation of distributional changes, is at any rate a partial cause in structural and functional ones ; while older explanations of these facts, even if not melting into merely abstractional ones, have not succeeded in gaining acceptance. At this point comes in with ponderous weight the con ception by which Lyell had for nearly thirty years been preparing the way for Darwin, that of uniformitarianism in natural change. For, although it was perhaps almost as much owing to the unfavourable opinion of Lyell as to the hostility of Cuvier that the doctrine of Lamarck had fallen into such disesteem, and although Lyell himself was accustomed "to keep the name of creation for a natural process which he imagined to be incomprehensible," he was, notwithstanding, as he claimed and as Huxley frankly allows, " strongly disposed to account for the origination of all past and present species of living things by natural causes," and his influence was, therefore, for Huxley, as no doubt for others, " perhaps more potent than any other in keeping alive a sort of pious conviction that evolution after all would turn out true." For, given the principle of Lyell s work, " the principle that the past must be ex plained by the present, unless good cause be shown to the contrary, and the fact that, so far as our knowledge of the past history of life on our globe goes, no other cause can be shown," it is evident that " consistent uniformi tarianism postulates evolution as much in the organic as in the inorganic world. The origin of a new species by 1 Romanes, Scientific Evidence of Organic Evolution, 1886. 2 Through reading Mai thus, On Population (see Ori/jin, p. 3 sy. ). It is worthy of notice also that Herder s early suggestion (vide supra) was made in his Philosojihy of History, Wells s early statement with respect to the races of man, and Patrick Matthew s in a treatise for practical purposes, while an early statement of the doctrine, hitherto apparently overlooked, was made with respect to machines by James Watt (</. Catalogue of Industrial Exhilrition, 1851). other than ordinary agencies would be a vastly greater catastrophe than any of those which Lyell successfully eliminated from geological speculation." Bearing in mind, then, the lesson of Lyell, that any efficient cause, even though slow or at first sight trifling, can be shown, if acting steadily for vast periods of time, to effect enormous results, the apparent difficulty of adding up varietal differences to specific ones, these to generic, and these again to still larger distinctions, becomes only the inevitable continuation of that summation of individual into varietal differences which no one can deny to be happening around us. Thus the onusprolandi that species have not arisen in this way comes fairly to be thrown by the advocates of natural selection upon its adversaries. And, as these come individually to realize, through those concrete studies which necessarily underlie all active con viction on one side or the other, the importance of the masses of concrete evidence which have been steadily accumulating, it is little wonder that their majority should not only have so rapidly dwindled, but actually have changed sides so generally as has been the case. Thus, to cite only a single case, (1) we are now in actual possession of an unbroken and geologically successive series of fossil horses, perfectly gradated through some forty -five "species" back to a five-toed ancestor ; (2) Ave can trace the con tinued evolution of the existing species in the bones, teeth, and finest peculiarities of the specimens around us, as well as the increasing differentiation of well-marked varieties through artificial selection ; (3) we can see that such con tinuous improvement of skeleton, teeth, etc., as is now and has all along been in progress, must have been profitable to the animals possessing them in the wild state, just as they now are in the tame (since implying better locomo tion, digestion, etc.). Hence we soon come to feel a real difficulty in understanding (1) how the continuous sum mation of small individual advantages through varietal characters into specific, and even generic ones, can be doubted, much less denied, and consequently (2) how the general applicability of the theory of natural selection to interpret the gradual process of historic change can any longer be called in question. At this point it is right to notice that several evolu- Varia- tionists have suggested or argued for the progress of tion variation along definite lines ; but this return upon pre- & , ! ^ Darwinian standpoints has been energetically and, it must ]j ues _ be admitted, on the whole as yet successfully combated. Thus Asa Gray (1861-76) has argued for variation along definite and useful lines. Niigeli (1865) regarded the ac quisition of certain characters which appear to be of no service to plants as offering a difficulty to natural selection, and as affording a proof of some innate tendency in plants towards perfection, corresponding to what Kolliker entitles the "law of creation." Mivart (1871) has maintained that variations are definite, and frequently sudden and considerable. With such positions must also be noticed the continuous and increasing insistence of Spencer (1852-86) upon environmental action and functional change, although spontaneous variation is not excluded nor considerable importance to natural selection denied. Butler in Eng land, and Cope, Hyatt, and other " Neo-Lamarckians " in America, have more fully developed this reaction, for which experimental evidence has been especially sought in Germany by Semper. And, while Darwin himself long continued an uncompromising opponent of all such heresies, a distinct, though partial, change of opinion was admitted by himself in later years, and has been fully insisted upon both by Mivart and Spencer. While in the Origin of Species up to 1869 variations are spoken of as "accidental" (no doubt only in that sense in which a scientific man may fairly
use the word), and there is ample proof of Darwin s origin-