VARIATION AND HEREDITY 123 



rence of a well-substantiated double-humped 

 curve not the result of modificational 

 effects may vividly bring home the fact that 

 the species is dividing into two sub-species. 

 Thus, by a statistical path, we are brought 

 face to face with the most vital of all facts 

 Involution cre"atrice. 



The rapidly growing body of facts in regard 

 to variation is also confirming what Darwin 

 called the " correlation of variations." He 

 pointed out that the whole organization is so 

 tied together during its growth and develop- 

 ment that, when slight variations in any part 

 occur, and are transmitted, and are accumu- 

 lated by natural selection, other parts of the 

 structure may also undergo change, apparently 

 irrespective of any advantage. The whole 

 framework is so knit together that if one 

 member suffer change others suffer with it. 



The idea of correlation suggests that the 

 organism often changes as a unity in many 

 parts at once, and not like a machine that is 

 perfected piecemeal by the accumulation of 

 many little patents independent of each other. 

 Thus a variation important in the present may 

 bring in its train one that is destined to be 

 important in the future, and a variation too 

 small in itself to be of value may be carried 

 over the dead point into effectiveness because 



