INTERNAL CAUSES OF VARIATION 



215 



Weismann reminds us that " by far the largest part of 

 qualitative modifications . . . rest on quantitative changes. 

 A determinant," says he, " must be composed of hetero- 

 geneous biophors, and on their numerical proportion reposes, 

 according to our hypothesis, their specific nature. If this pro- 

 portion is altered, so also is the character of the determinant ; " 

 and further : " for fluctuations of nutriment and the struggle 

 for nutriment, with its sequent preference of the strongest, 

 must take place between the various species of biophors as 

 well as between the species of determinants. But changes in 

 the quantitative ratios of the biophors appear to us qualitative 

 changes in the corresponding determinants." 1 And again : "By 

 a selection of the kind referred to the germ is progressively modi- 

 fied in a manner corresponding with the prodttction of a definitely 

 directed progressive variation of the part ! ." 2 In this way Weis- 

 mann would " explain " Eimer's orthogenesis ; but it is note- 

 worthy that none of the theories yet proposed will account for the 

 original introduction of a new character in the race, whether 

 represented and transmitted by a physiological unit or not. 

 Germinal selection would provide for changes in relative pro- 

 portions of characters, and even for their utter extinction, but 

 not for their introduction, unless, indeed, characters may origi- 

 nate by new combinations of old elements. 



One is almost forced to the conclusion that in nature loss 

 or modification of characters is far more common than their 

 origin and introduction. It looks as though most of the changes 

 arise in this way, yet it is conceivable that an entirely new 

 quality might arise through a relatively slight modification of 

 the chemical or physiological make-up of the vital units. It is 

 seen and recognized that in the non-living world a slight change 

 in the radical is followed by a profound alteration in physical 

 and chemical properties, and that this sweeping change may be 

 induced by comparatively slight and even external causes. 

 May not the same be true of vital radicals or units, and may 

 not new characters arise more readily than we suppose, all per- 

 haps out of elements fewer, and transformations simpler, than 

 we have hitherto imagined ? 



1 Weissman, On Germinal Selection (second edition), pp. 46-47. 2 Ibid. p. 35. 



