VARIATION AND HEREDITY 119 



racial importance of modifications, it is of 

 interest to notice Darwin's view of the 

 relative importance of "single variations'* 

 and "individual variations." The former 

 correspond in a general way to what we 

 now call "discontinuous variations," "muta- 

 tions," "saltatory variations"; the latter to 

 " continuous variations" or "fluctuations." 

 Darwin was much interested in the former 

 class, "sports" as he sometimes called them; 

 but true to the influence of Lyell he came 

 deliberately to the conclusion that the minute 

 ubiquitous fluctuations were by far the more 

 important. The criticism of Fleeming Jen- 

 kin, Professor of Engineering in Edinburgh, 

 that single large peculiarities would be likely 

 to be swamped by inter-crossing, had so 

 much weight with Darwin that he ceased to 

 attach importance to the larger divergences, 

 and found his raw material in the smaller 

 fluctuations. "The more I work," he said, 

 "the more I feel convinced it is by the ac- 

 cumulation of such extremely slight varia- 

 tions that new species arise." We shall 

 return to this question, but we may note in 

 passing (1) that there is no reason to believe 

 that "single variations" necessarily occur 

 singly, the fact being that numerous sports 

 in the same direction sometimes occur simul- 

 taneously; (2) that some of the discontinuous 



