l.'iO THE i;\x>u rioN thkokv 



yonniual ttuduatiiMi.s of imtrition. this is tnuismitteil to tho 

 dosccTulants just as woll as tho normally dovolopt-d or^an, and in 

 the course ot" o-enerations will be inherited hy a greater and greater 

 mnuher of individuals, and must ultimately be inherited by nil in 

 some degree or other. The object ion has been urged from many 

 sides that variations upwards would be tjuite as likely (o arise as 

 those downwards, but this is an i>rror. Even if, at the lu'ginning. 

 the minus-variations were rarer than the plus- variations, in Ihe 

 eourse of geneT'abions the minus ones would preponderate because 

 ascending xariatious of disused organs are not inditt'erent for I lie 

 organism but injurious to it. Perliaps an increase in the size ol' tlu> 

 organ itself would do no harm, but in that ol" its determinant 

 it certainly would, because an ascending determinant rei|uires more 

 nourishment than pre\io\isly, and withdraws it from its surroundings, 

 and thus from the determinants ii\ its in\mediate neiglibourhood ; 

 but these are tluise of functioning and indispensable parts. Individuals 

 in whose germ-plasm tlie determinants of disused organs ase(>iid, and 

 thereby depress the determinants of organs which twv still acti\(\ 

 are subject to personal selection, and are eiimiuatt'd. There thus 

 ren\ain only those with descending determinants; in other words, 

 the chance of variants in the direction of weaknt'ss in useless deter- 

 minants far outweiglis that of variants in the dii'ei'tion of inci-eased 

 strength : the latter will soon cease to occur at all, for as soon 

 as a determinant has fallen a little .Ih'Iow its nortnal level, it linds 

 itsc'lf upon an inclined pljuie, along which it glides very slowly 

 Imt steadily downwards. This might be disputed if it could be 

 maintained that, at e\cry stage of the descent, a. change of dii'ection was 

 possible. But this probably takes plac(> rarely and only in the case 

 of individual ids, and will therefoi-e not be permanent because 

 iu giMieral the stronger neighbour determinants will possess them- 

 selves of the supertluous nourishment, and a lasting asci-nt will thus 

 be impossible to the wi'akened determinant. This is precisely wliat 

 I have called (iern\inal Selection. The deti'rminant whose assimilat- 

 ing ])ower is weaki'ued by ever so little is continually lu'ing robbed 

 b}' its neighbours of a part of tlu' noui'ishnient- which Hows towards 

 it, and uuist consecpiently become fui'tliei' weakened. As no mori- 

 help will be given to it by natural selection, .since the organ is no 

 longer of any \alue to the species, the belter among the weakened 

 determinants of N ai'e u(^ver seU>ct'iHl out, and they must, gradually gi\'(^ 

 way iu the struggi(^ with the neighbouring (lelerniiuanls which ai'i^ 

 necessary to tho species, boconnng gra,(hially wea,ki>i' and ultimately 

 disappoai'ing. 



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