OKKMINAI, SF.l.KCTrON 1:J7 



of oquili\u-ium that ha.s oiuv Invn attnined liy thoilotorminant system 

 \vhono\ or it is disturWd ? 



It is ditttoiilt to orivo any oontidtMit answor to this question. Wo 

 cannot ivaeh i'loan>ossoi\ this point thnwgh o\ir pivsont knowUHloc of 

 tho >;vvni-plasin, Ivoauso wo possess no insij^lit into its stniotnre ; wo 

 can only draw eonchisions as to tlio ]irooossos in tlio o;cvm-pla.sni from 

 the oKsorxod phonomona of \ariation and inhoi-itrtiu-o. But two facts 

 stAnd in diroot antithesis to one anotliov, fii-st. the l\ii;li powor of 

 adapt<\tion ^xissossoii hy all spot'ios. and tho nndonhtod occurronco of 

 nnivstriotod poi-sistonoo in a pfivon direction of variation, as soon in 

 art.itioial selection, and in the dissippoaranco of parts which haxe 

 coasod to function ; and, secondly, tho oreat const.-nicy of oUi-estab- 

 lishtnl species -wlnoh do indeed always exhibit a certain doo-roe of 

 individ\ia.l variability, but without showing- marked deviations as 

 a frequent oixninvnoe or in aJl possible diivctions. as they certainly 

 would if every detentiinaivt favouivd by a chance increase in the 

 nutritive snvant necessarily and irresistibly wont on varying- further 

 in the s;une diivetion. C^r cai\ the ivnstanoy of such species be main- 

 t.ainei.1 solely by means of personal selection, which is continually 

 settino; aside {\11 the detorntinaiits which rise alxne the selection-value 

 hy eJiminatinjj their possessors ? 1 was for lonjj satisfied that this 

 wa.s the true solution of the ditfic\ilty. and even now I do not dinibt 

 that jxu-sonal seUM?tion does, in |x>iut of fact, maintain the constancy of 

 the species at a ivrtaitt level, Init I do not Mieve that this is snthcient, 

 bin rather that it is mvess;ny to rect^gni/.e an equalizing inriuence 

 due to ijerminal selection, and to attribute to this a share in maintain- 

 ine- the Ciinstancy of a species which has lono; been \vell adapted. 

 I am lixi to tl\is assumption chiefly by the phenomena of n ariation in 

 Man. for we tind in hi»n a tluitisjvnd kinds of minute herinlitary 

 individual vaiiations. of which not one is likely to att^\in to selection 

 value. t~)f ct>ui-se the const.ant recurrei\ce of riHlucin<x divisioi\s 

 pivvents any pxrtieular id which contains a varying determinant fivni 

 \h ine- inherittxi throusjh inauy gcMiettxtions : for so many ids are being 

 Cv>ntiintal]y nMuovini fixnn the g«.>noalogical trt^ by the constant 

 n^jeetion of the half of jUI ids of every germ-plasni. that only a snuill 

 ]Virt of the ancestral id tvnuvins in the grandchild, great-grandchild, 

 and so iw. Certainly some of the ids of the ancestors compose the 

 g\M-m-plasn\ of the descendants, aud if all the determinants of one 

 of these ids had begun to vary jx>i-si stent ly upw.aixls or downwaixis in an 

 anct\stor, tlveivall the determinants of the ivlative id in the descendants 

 would possess the variation in an intettsitieil degree ; and however 

 slowlv the N ariation advaitivd it would attain selection-value in some 



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