Statement of Weismann s System (1886). 13 



the limits of fertility, and, therefore, that can ever 

 become actual in living organisms. In point of fact, 

 Weismann believes — or, at any rate, provisionally 

 maintains — that this is the sole and only cause of 

 variations that are congenital, and therefore (according 

 to his views) transmissible by heredity. Now, whether 

 or not he is right as regards these latter points, I 

 think there can be no question that sexual propagation 

 is, at all events, one of the main causes of congenital 

 variation ; and seeing of what enormous importance 

 congenital variation must always have been in 

 supplying material for the operation of natural se- 

 lection, we appear to have found a most satisfactory 

 answer to our question, — Why has sexual propagation 

 become so universal among all the higher plants and 

 animals ? It has become so because it is thus shown 

 to have been the condition to producing congenital 

 variations, which in turn constitute one of the primary 

 conditions to the working of natural selection. 



Having got thus far, I should like to make two or 

 three subsidiary remarks. In the first place, it ought 

 to be observed that this theory touching the causes of 

 congenital variations was not originally propounded 

 by Professor Weismann, but occurs in the writings of 

 several previous authors, and is expressly alluded to 

 by Darwin 1 . Nevertheless, it occupies so prominent 

 a place in Weismann's system of theories, and has by 

 him been wrought up so much more elaborately than 

 by any of his predecessors, that we are entitled to 

 regard it as, par excellence, the Weismannian theory of 

 variation. In the next place, it ought to be observed 

 that Weismann is careful to guard against the 

 1 E.g., Variation, &c, vol. i. pp. 197, 398; vol. ii. pp. 237, 252. 



