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Show 82 DARWINISM onAP. HI the last edition of Jl/11' Origin of Specif's was prepared; :.mel it i~ clear that Mr. Da,rwin himself did not fully recognise lhc enormous amount of variability that actually cxi ts. This is indicated by his frequent reference to the extreme slowness of the changes for which variation furnishes the material s, and also by his usc of such expressions as the following : " A va,ricty when once formed must again, pe1'haps after l£ long inlm·val of tirne, va,ry or present individual differences of th • same favourable nature as before" (Origin, p. 66). And agn,in, after speaking of changed conditions "affording a better ch:tncc of the occurrence of favourable variations," he adds: "lJnless such occw· nat'uml selection can do nothing" (Origi11, p. 64). These expressions arc hardly consistent with the bet of the constant a,nd large amount of variation, of every part, in all directions, which evidently occurs in each gencrn,tion of all the more abundant species, and which must afford an ample supply of favonra.ble variations whenever required ; and they have heen Roizccl upon and exaggerated by , omc writers as proofs of the extreme difficulties in the way of tl1e theory. It is to show that such difficulties do not exist, and in the full conviction that an adequate knowledge of tll <' facts of variation affords the only sure foundation for the Darwinian theory of the origin of species, that this chapter has been written. CHAPTER IV VARIATION OF DOMESTI ATED ANIMALS AND CULTIVATED PLANTS The fac~s ?f variati.on. and artificial selection- Proof: of the generality of val'l~ti?u-V anatwns of apples and melons- Variations of flower.·Var~ atwns of domestic animals - Domm;tic pigcous- Acclimati atiou -Circumstances favourable to selection by man- Couditions favourable to variation-Concluding remarks. HAVING so fully discussed variation under nature it will be unnecessary to devote so much spn.ce to dome ticatcd animals and cultivated plants, especially as Mr. Darwin has published tw~ r~markable v_olumes on the subject where those who desire It m~y obtam ample information. A general sketch of the more 1mport_ant facts will, however, be given, for the purp~se o~ showmg h?w closely they correspond with those described I~ t~e preced!ng chapter, and also to point out the general prme1plcs whiCh they illustrate. It will al. o be necessary to explain how these variations have been incrca.. c<l and accumulated by artificial selection, since we are ther ·by better enabled to understand the action of natural selection to be discussed in the succeeding chapter. ' The facts of Variation and A1·tificial Selection. Every one knows that in each litter of kittens or of puppies no two are alike. Even in the case in which several are ex~ctly alike in colours, other differences are always P?rce~tibl~ t~ those who observe them closely. They will differ m size, m the proportions of their bodies and limbs in ~he le~gth. or ~e.xture of their hairy covering, and not;bly m their dispositiOn. They each possess, too, an individual |