Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/97

VARIATION 81 ally even contemptuous attitude towards Lamarck, and of his substantial rejection of the comparative importance of function or environment in determining variations, these views are unquestionably modified in the well-known pero ration to the Origin of Species. The further diminishing importance of natural selection is admitted in subsequent editions, as Spencer has pointed out, in the preface to the Descent of Man, and indeed elsewhere ; while a recent pungent criticism l cites evidence of a certain measure of ap parently contradictory and indefinite fluctuation of opinion between increased insistence upon use and disuse on the one hand and upon spontaneous variability on the other. leas for Since, however, Darwin never developed the grounds of this diminishing reliance upon natural selection, which still 11 ! :e ,. remains the central theme of his works, and that upon which their originality, as well as their importance to the theory of evolution, essentially depends (of course as dis tinguished from their services in summing up the concrete evidence for the fact of evolution and their vast utility in diffusing it), too much weight must not be attached to such isolated expressions of opinion as those referred to above, the more so as these are nowhere borne out by any general change in the tenor of his works. In the absence of any theory of definite and progressive change, and in the presence of multitudinous variations under domestication and in nature which we can neither analyse, rationalize, nor hardly even classify, we are not only justified bxit logically compelled to regard variation as spontaneous or indefinite, i.e., practically indeterminate in direction, and "therefore Unimportant, except as the groundwork for selection to act on." Conversely, variation must be in definite, else the paramount importance of natural selec tion must be proportionally impaired as this becomes de finite (rf. EVOLUTION, vol. viii. p. 751); for we cannot speak of selecting a course from one line of variation, nor even for that matter in the old sense of "variation" at all. Thus, "if it should hereafter be shown that variability is definite and determined in certain directions rather than others" (in short "fated" rather than "spontaneous"), "the importance of natural selection would not be im paired," since it would still have to be regarded as a vera causa in the history of species, yet the function ascribed to it would be practically reversed. It would exchange its former supremacy as the supposed determinant among the indefinite possibilities of structure and function for that of simply accelerating, retarding, or terminating the process of otherwise determined change. It would furnish the brake rather than the steam or rails upon the journey of life ; or, in other words, instead of guiding the ramifica tions of the tree of life, it would, in Mivart s phrase, do little more than apply the pruning knife to them. 2 In fact, its functions would be restricted to those of the third Fate, and would no longer, as at present, be supposed to in clude those of the second. Under these circumstances it is unnecessary to appeal at length to the unanimity with which the later generation of Darwin s exponents (e.g., Lankester, Romanes, Allen, <tc.) concur with all preceding ones in the necessary proposition, that " natural selection trusts to the chapter of accidents in the matter of variation." The thesis thus summarized by Lankester thoroughly permeates the Variation of Animals and Plants vnder Domestication, as may be seen from the brief sum mary of it given below (p. 82). 3 Special reference must, however, be made to the important researches of Weis- mann, 4 since these were devised with the deliberate inten- 1 Butler, Luck or Cunning, London, 1887, chap. xii. ; see also his Evolution, Old and New, London, ] 879. - "On the Theory of Individuality," in Proc. Roy. Soc., 1886. 3 See, however, chapter xxi. of Variation, &c., conclusion. 4 Studies in the Tlieory of Descent, Eug. ed., London, 1882. tion of testing " whether, besides natural selection and the direct action of external conditions, together with the correlative results of these two factors, there might not lie concealed in the organism some other transforming power," such as the " perfecting principle " of Nageli or the like. The results of these investigations have tended entirely to confirm the theory of natural selection in its classic form ; moreover, the same naturalist has since ad duced weighty arguments against the transmissibility of individual variations, 5 whether acquired by habit or im pressed by environment, and thus proportionally weakened the arguments of Spencer and others in favour of the revival of the Lamarckian factors of change. Variation seems therefore to be driven in more and more upon the reproductive function, and thus an ultra-Darwinian in sistence upon the obscure and as yet wholly indefinite factor of variation is strongly forced upon us, and natural selection seems more than ever to be our only possible clue. Armed, however, with this, we have a consistent means Darwin s of re-investigation of the whole organic world, in the course ^io- of which, not only our existing accumulations, as of tax- logi ^ onomy and of comparative anatomy, acquire a new interest, ^ and all existing lines of research receive a potent stimulus, but the marvellous variety of adaptation comes into in telligibility and order, a new teleology thus replacing the old. Of this profound change in the standpoint and interest of modern biology we can form an idea most simply, yet most representatively, by glancing at Darwin s own biological works. Before the Origin of Species we have the slow and laborious production of the substantial, yet conventional and comparatively arid, Zoology of the Beagle and Manual of the Cirripedia, while afterwards the well-known and fascinating new series of zoological and botanical discoveries and generalizations were poured out with remarkable rapidity. The many bold and ingenious applications of the theory of natural selection which we owe to Darwin and his school should here be reviewed seriatim ; but it is impossible to do more than mention some of them, e.g., the renascence and development of SprengePs discovery of the relations of flowers to insects, the elaborate studies on Fertilization in Orchids, the Forms of Flowers, Insectivorous Plants, Climbing Plants, Movement in Plants, &c. Again, the interpretation of the problems presented by bee and ant society led him to grapple with the problems of mind and language, in the Descent of Man and the Expression of the Emotions ; and the systematic application of the conceptions of biological science to those of psychology, sociology, and ethics, which had been com menced by Comte and continued by Spencer, rapidly passed from its comparative philosophic isolation into wide diffu sion through the movement of literature and science. 6 This passage from the inductive verification of the Applica- theory of natural selection to its deductive application as tion of an engine of research is conspicuously associated with the gotten labours of Haeckel, whose Generelle Morphologic (1866) to Lio- and other minor works have a central historic place amid logical the first fruit and seed of the new movement in German sc i ence ; biology, which was henceforward almost completely Dar winian ; and they have equally strong claims, to be con sidered as the starting-point of those logical and unflinch ing attempts to view all problems in the light of natural selection which have since become more common. By transcending the limits of ordinary biological specialism independently of Darwin, and dispensing with his initial 5 The reservations with respect to niiud and language made by evolutionists so contrasted in many respects as Wallace and Mivart should here be mentioned ; see Mivart s Lessons from Nature, also his "Limit to Evolution," in Nineteenth Century, 1884. 6 Die Continuitat d. Keimplasmas, Jena, 1885, and Die Bedeutuny d. sexudlen Fortpflanzung, Jena, 1S&6.

XXIV. ii