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Show 142 DARWINISM CllAP. of adaptations which are usually co~~on to many species, or, more Commonly to o-cnera and families; but, I urge further, it has not eve'n bebe n proved that an~ tru1 y . " spe01' fi ~ " characters-those which either singly or. m combma~wn <hstinguish each species from .its nearest .alhcs-,are entirely .1m~ adaptive, useless, and mcanmgle~s ; while a gr cat body of fa.ctfi on the one hand, and some wmghty arguments on the other, alike prove that specific characters have been, a~d could onl} have been, developed and fixed by natural selectwn because of their utility. W c may admit, that among the great num bcr of variations and sportswhichcontinuallyarise many ~rc altogether useless without being hurtful; but no cause or mfiucncc ha::; been adduced adequate to render such characters fixed :Lll(l constant throughout the vast number of individuals which collstitute any of the more dominant species.! The Swamping Effects of Interc1·ossing. This supposed insuperable difficulty was first advanced in an article in the North British Review in 1867, and mn<'h attention has been attracted to it by the acknowledgment of Mr. Darwin that it proved to him that "single vn,riationR," or what are usually termed "sports," could very rarely, if eYer, be perpetuated in a state of nature, as he had at first t~onght might occasionally be the case. But he had always con s1d c~·ed that the chief part, and latterly the whole, of the matcrmls with which natural selection works, was afforded by individ ual variations, or that amoul}t of ever fluctuating variability which exists in all organisms and in all their parts. Other ·wrii rr::> have urged the same objection, even as against indiviclnal variability, apparently in total ignorance of its amount anrl range; and quite recently Professor G. J. Romanes has adduced 1 Darwin's latest expression of opinion on thi. question is interesting, sitH'l' it shows that he was incli11ed to rctum to !tis earlier view of the gt ll l'ral , or universal, utility of specific characters. In a letter to ' cmpcr (80th ?-io1. 1878) he writes: "As our knowledge advances, very slight difl"crcll ccs, l'Ollsidered by systematists as of no importmlCe in structure, are continu ally found to be functionally important; and I have been especially struck 11illt this fact in the case of plants, to which my ol,servations have, of late )"l':trs, been confined. 'l'herefore it Reerns to me rath er rash to co m:i!l er slight differences between representative species, for instance, those inltal,il ing tltB different islands of the same archipelago, as of no fun ctional intporl.!tll l'l', awl as not in any way due to natural selection" (Life of Dcmcin, vol. iii. p. llil). VI DIFFICULTIES AND 0BJEC1'IONS 143 it as one of the difficulties which can n.lone be overcome by his theory of physiological selection. He urcres, that tho umc variation docs not occur simultaneously bin a number of individuals inhabiting the same area, and that it is mere assumption to say it docs; while he admits that "if the a~surnption wm:e grante~ there would be an end of the present difficulty; for 1f a sufficJCnt number of individuals were thus simultaneously and similarly modified, there need be no lono-er any dn,ngcr. of the variety becoming swamped by intcrcrossin~. " I must agam refer my readers to my third chapter for the proof that such simultaneous variability is not an assumption but a fact; but, even admitting this to be proved, the problem is not altogether solved, and there i. so much misconception regarding variation, and the actual process of the ori o-in of . . b new spccJCs IS so obscure, that some further discussion n,nd elucidation of the subject arc desirable. In one of the preliminary chapters of Mr. Seebohm's recent work on the Chamd1·'iidce, he discusses the differentiation of species; and he expresses a rather widespread view amonO' naturalists when, speaking of the swamping effects of inte~ crossing, he adds : "This is unquestionably a very grave difficulty, to my mind an absolutely fatal one, to the theory of a~cidental variation." And in another passage he says: "The simultaneous appearance, and its repetition in successive o-encrations, of a beneficial variation, in a hrge number of individ~w.ls in the same locality, cannot possibly be ascribed to chance." These remarks appear to me to exhibit an entire misconception of the facts of variation as they actually occur, and as they have been utilised by na.tural selection in the modification of species. I hav~ already shown that every part of the organism, in common spec10s, does vary to a very considerable amount, in a large number of individuals, and in the same locality ; the only point that remains to be discussed is, whether any or most of these variations are "beneficial." But every one of these variation. consists either in increase or diminution of size or power of the organ or faculty that varies ; they can all be divided into a ~ore effective and a less effective group-that is, into one that IS more beneficial or less beneficial. If less size of body would be beneficial, then, as half the variations in size arc above and half below the mean or existing standard of the species, there |