432 THE GERM-PLASM 



with a single one. The process of a/np/ti)nLvis alone rendered 

 it possible for such manifold combinations of characters to be 

 offered to selection, so that the proper choice could be made. If 

 the view which I have long held is correct, a single character 

 is never alone acted upon by natural selection, but the whole 

 aggregate of specific characters is incessantly exposed to this 

 process. The constancy as well as the transformation of the 

 existing specific characters, the removal of superfluous ones, 

 and the development of new characters, is due to the incessant 

 and uninterrupted control of selection. This is only rendered 

 possible by the continual intermingling of all the existing 

 varieties of characters, which can only be effected by amphi- 

 mixis. Hence, although the latter process is not the primary 

 cause of individual variation, it is nevertheless an indispensable 

 factor in selection, for by its means alone can the material from 

 which variations arise be so arranged that selection can operate. 



The theory of variation here propounded also affords a more 

 satisfactory explanation of a further difficulty than can be 

 obtained by any other. In considering the unlimited number of 

 adaptations of organisms to the conditions of existence, we 

 must be surprised at the wonderful plasticity of the species. It 

 gives us the inpression that every variation, however unexpected, 

 might be produced by a species as soon as the species has 

 use for it. On reflecting how certain animals and plants, or 

 parts of plants, are imitated in colour, form, and marking by 

 other animals, we might be inclined to suppose that every part 

 of an animal may assume any required form, colour, or marking, 

 according to requirement. 



This must not, however, be taken literally ; an organism 

 cannot assume every form, though it may become adapted in so 

 many ways that we cannot possibly attribute its immense 

 number of adaptations to rare, fortuitous variations, occurring 

 only once. The necessary variations from which transformations 

 arise by means of selection, must in all cases be 'exhibited over 

 and over again by many individuals. 



The presence of such an ever active material for primary varia- 

 tions is a direct consequence of the theory here propounded, 

 according to which every part or 'determinate' of a species must 

 present every possible variant in different individuals in the course 

 of generations, and will sometimes be represented in a larger, 

 and sometimes in a smaller majority of modified ids. Since an 



