Stability with Change 373 



advantage except after many accumulations of small steps. 

 Of course Darwin insisted upon the small, almost imper- 

 ceptible steps, because this seemed to avoid the metaphysical 

 difficulty. If the steps are small enough, they come within 

 our everyday experience and do not need to be accounted 

 for as something distinct from the facts of life in general. 



The first definite criticism of Darwin's theory from this 

 point of view seems to have been made, in 1864, by the 

 zoologist Albrecht von Kolliker, who gave to the process of 

 variable heredity the name heterogenesis — that is, the crea- 

 tion or birth of something that differed from the parents. 

 This process, in theory, was compared to the formation of 

 different molecules of chemical substances by the change of 

 one or more atoms. It was assumed that each species was as 

 distinct from others as is one chemical substance from an- 

 other. Sodium sulfate differs from sodium bisulfate, for 

 example, in that one atom of sodium in a molecule of the 

 former has been replaced by an atom of hydrogen. There 

 are no intermediate substances. In the same way there are 

 no strictly intermediate forms between one species and the 

 next, but there is a distinct jump from one to the next. It 

 was necessary, according to this idea, to redefine species so 

 that forms which are alike in most characters but differ 

 in only one or two minor points are to be considered true 

 species, or, as they were sometimes called, " elementary spe- 

 cies." Kolliker conceived evolution to come about, then, by 

 heterogenesis, or the appearance of forms that were at the 

 same time distinct from their parents and yet capable of 

 passing on their own distinct traits to their offspring. 



Stability with Change 



The word stability suggests something anchored firmly 

 in the rock bottom of the universe, or at least of the world. 

 But that conception is relative, in the sense that there may be 

 many degrees of stability. And it is compatible with change 

 or movement. The earth, for example, is stable. We do 



