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Show 418 DARWINISM CHAP. not have been effected by "simultaneous fortunate spont:meous variations." But this difficulty is fully disposed of by the facts of simultaneous variation adduced in our third chapter, and has al. o been specially considered in Chapter VI, p. 127. The best answer to this objection may, perhaps, be found in the fa.ct that the very thing said to be impossible by variation and natural selection has been again and again effected by variation a,nd artificial selection. During the process of form ation of such breeds as the greyhound or the bull-dog, of the race-horse ~tnd cart-horse, of the fantail pigeon or the ottersheep, many co-ordina,te a.djustments have been produced; and no difficulty has occurred, whether the change has been effected by a single variation- as in the last case named- or by low steps, as in all the others. It seems to he forgotten tha,t mo. t animals have such a surplus of vitality and strength for a,ll tho ordinary occasions of life that any slight superiority in one p:ut can be at once utilised; while tho moment any want of balance occurs, variations in the insufficiently developed p:trts will be selected to bring back the harmony of the whole organisation. The fact that, in all domestic animals, variations do occur, rendering them swifter or stronger, ln.rger or smaller, stouter or slenderer, a,nd that such variations can be sepamtoly selected and accumulated for man's purpose , i snffi ci 'nt to render it certain that similar or even greater changes m:1y llo effected by natural selection, which, as Darwin well remarks, "acts on every internal organ, on every shade of constitntutional difference, on the whole machinery of lifo." Tho difficulty as to co-adaptation of part. by variation and n;ttmal selection appears to me, therefore, to be a wholly imaginary difficulty which has no place whatever in the operations of nature. Direct Action of the Envi1·onrnent. Mr. Spencer's last objection to the wide scope given hy Darwinians to the agency of natural selection is, that organ ism. are acted upon by the environment, which produces in them definite changes, and that these changes in the individnal arc transmitted by inheritance, and thus become increased in successive generations. That such changes are producctl in the individual th~re is ample evidence, hut that they arc in- XIV FUNDAMENTAL PROBLEMS 419 herited independ.ently of any form of selection or of reversion is exceedingly doubtful, and Darwin nowh~re expresses himself as satif>fie~ with the evidence. The two very strongest cases he mentwns are the twenty-nine species of American trees which all differed in a corresponding way from their nearest European allies ; and the American maize which became changed after three generations in Europe. But in the case of. the t:ees the ~ifl'erences alleged may be partly due to. correlatw:r: with constitutional peculiarities dependent on chma,te, especmlly as regards the deeper tint of the fadinO' leaves and the smaller size of the buds and seeds in America ~han in Europe ; while the less deeply toothed or serrated leaves in the American species are, in our present complete ignorance of the cau es and uses of serration, quite as likely to be due to some form of adaptation as to any direct action of the climate. Agair~, we ~re not. told how many of the allied species do not vary m th1s particular manner, and this is certainly an important factor in any conclusion we may form on the question. In the case of the maize it appears that one of the more remarkable and highly selected American varieties was cultivated in Germany, and in three years nearly all resem? lance to the original parent was lost; and in the sixth year 1t closely resembled a common European variety, but was of somewhat more vigorous growth. In this case no selection appears to have been practised, and the effects may have been due to that "reversion to mediocrity" which invariably occurs, and is more especially marked in the case of varieties which have been rapidly produced by artificial selection. It may be considered as a partial reversion to the wild or unimproved stock; and the same thing would probably have occurred, though perhaps less rapidly, in America itself. As this is stated by Darwin to be the most remarkable case known to him "of the direct and prompt action of climate on a plant," we must conclude that such direct effects have not been proved to be accumulated by inheritance, independently of reversion or selection. The remaining part of Mr. Spencer's essay is devoted to a consideration of the hypothetical action of the environment on the lower organisms which consist of simple cells or formless masses of protoplasm ; and he shows with great |