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Show 412 DARWINISM CHAP. improved races of pigs-the two latter ex:1m1~les being quoted from Mr. DanYin, - and other cases o_f hke. nature. As examples of the latter, Mr. Darwin IS .agam quot.ed as admitting that there n,re many cases in which the actwn. of similar conditions appears to have produced correspondmg changes in different species; and we h~ve ~ very. el~borate di. cussion of the direct action of the medmm m mochfymg the protopla.. m of simple organisms, so n.s to b~ing about the difference bet·ween the outer surface and the Ill ncr part that characterises the cells or other units of which they are formed. Now althouo-h this essay did little more than bring together facts which had been already adduced by Mr. Darwin or hy Mr. Spencer himself, and laY: stress upon th~ir impo_rtance, its publication in a popular reVIew was I:nmed1~tely seized npon as "an avowed and definite declarat10n aga.mst some of the leading ideas on which the Mechanical Philosophy clepenc!:-;," and as beino· "fa,tal to the adequacy of the Mechamcal Philosophy abs any expla~at. wn o f orgam.c ev_o 1u t'w n, "I -an expression of opinion whiCh would ?e repudu~ted b~ every Darwinian. For, even admitting the mterpretatwn whiCh Mr. Spencer puts on the facts he adduces, the;y are all in?lnded in the causes which Darwin himself recogmsed as havmg acted in brino-ino- about the infinitude of forms in the organic world. In the eco~cludino· chapter of the 01·igin of 1 11ecies he says : "I have now rec:pitulated the facts and considerations which haYe thoroughly convinced me that species have been modified dnrino- a lono- course of descent. This bas been effected b b • chiefly through the natural selection of nu:nerous successive, slight, favourable variations; aided in a~ Important manner hy the inherited effects of the use .an~ d1sus~ of parts; a_ml in an unimportant manner-that 1s, m relat1~n to ad~pLIY~ structures whether past or present, by the d1rect action of external conditions, and by variations which seem to us, in our io-nomnce, to arise spontaneously." This passage, .·nmmarisi'ng Darwin's whole inquiry, and explaining his final point of view, shows how very inaccurate may be the popular notion, as expressed by the Duke of Argyll,. of any supp~scd additions to the causes of change of species as r ecogmsccl by Darwin. 1 See the Duke of Argyll's letter in Natm·e, vol. xxxiv. p. 336. XIV FUNDAMENTAL PROBLEMS 413 But, as we shall see presently, there is now much reason t? believe t~at the supposed inheritance of acquired modificatiOns- that IS, of the effects of usc and disuse or of the direct influenc? of ~be environment-is not a fact; a~d if so, the very foundation Is taken away from the whole class of objections on which so much stress is now laid. It therefore becomes important to inquire whether the facts adduced by Darwin, Spencer, and others, do really necessitate such inheritance or whether any other interpretation of them is possible.' I belie.ve there is such an interpretation; and we will first consider the cases of disuse on which Mr. Spencer lays most stress. The cases Mr. Spencer adduces as demonstrating the effects of disuse in diminishing the size and strength of oro-an are the diminished size of the jaws in the races of civjli~ed men' and the diminution of the muscles used in closing the jaws i1~ the case of pet-dogs fed for generations on soft food. He argues that the minute reduction in any one generation could not possibly have been useful, and, therefore, not the subject of natural selection ; and against the theory of correlation of the diminished jaw with increased brain in man, be urges that there are cases of large brain development, accompanied by jaws above the average size. Against the theory of economy of nutrition in the case of the pet-dogs, he places the abundant food of these animals which would render such economy needless. But neither he nor Mr. Darwin bas considered tho effects of the withdrawal of tho action of natural selection in keeping up the parts in question to their full dimensions, which, of itself, seems to me quite adequate to produce the results observed. Recurring to the evidence, adduced in Chapter III, of the constant variation occurring in all parts of the organism, while selection is constantly acting on these variations in eliminating all that fall below the best working standard, a~:d preserving only those that are fully up to it; and, remembering further, that, of the whole number of the increase produced annually, only a small percentage of the best adapted can be preserved, we shall see that every useful organ will be kept up nearly to its higher limit of size and efficiency. Now Mr. Galton bas proved experimentally that, when any part bas |