WHA T IS EVOLl 'ED IX E \ 'OL U TION ? 2/3 



tion. Both are at work at the same time, and every organism 

 has its specific, its generic, and family characters, and those 

 of higher order. Varietal characters in the process of ex- 

 trinsic evolution may become invariable, and be ranked as 

 specific accordingly; but when a character becomes fixed it is 

 no longer variable, and because one species differs from an- 

 other, and one genus from another, it does not follow that a 

 specific character has by degrees become of family or ordinal 

 rank. On the contrary, the cessation of plasticity which 

 results when the varietal character becomes transmitted with- 

 out change, and thus characterizes the species, makes it logi- 

 cally impossible to account for the difference in rank of the 

 characters of an organism by any evolutional process. Rank 

 of characters of the organism, as expressed in their place in the 

 classification, is inherent in their use; and the same laws which 

 are engaged in the origin of specific characters must also 

 account for the origin of ordinal characters. The specific 

 character does not become of ordinal rank, but whenever an 

 ordinal character arose it must have first appeared as a variety. 

 Herein consists the great importance of the facts of variation. 



The accumulation of varietal modifications of parts or 

 their intensification, their growing larger or smaller, stronger 

 or weaker, is a matter fundamentally of addition or subtrac- 

 tion in the component units of lower order. Given a tissue 

 made up of cells and performing a given function, and the 

 modification of its form is but an expression of increased 

 growth at one place or diminished growth somewhere else. It 

 is easy to imagine conditions of environment, use, and dis- 

 use, adaptation to existing conditions or the opposite, as 

 resulting in the modification of the form of the organ. 



It is not difficult to imagine the same kind of phenomena 

 working a selective discrimination among the variable degrees 

 of such adaptation, and resulting in the preservation of cer- 

 tain variations and the elimination of others in the stru<icrle 

 for existence. The theory of origination of species by natu- 

 ral selection applies to cases of extrinsic evolution ; but it is 

 difficult to imagine how natural selection can operate in the 

 production of the differences in structure which must be 

 alreadv differentiated before their relative fitness or unfitness 



