CHAP, xvn METAPHYSICS OF NATURAL SELECTION 197 



Force and Force. Symmetry with what has gone 

 before would lead us to head our next paragraph with 

 these words. But it is questionable whether we can 

 fairly charge Darwin with treating the different bio- 

 logical forces involved in natural selection life, 

 variability, heredity as mutually independent and 

 merely coincident things. Scientific logic may in- 

 cline students of science to do this, but a wholesome 

 sense of biological realities will keep them in check. 

 Where Darwin is open to question in this re- 

 gion is in his doctrine of variability. Is variation 

 related in any intelligible fashion to heredity ? Or is 

 it purely " casual " ? Perhaps we shall find that Dar- 

 win emphasises the mechanical blending of distinct 

 heredities that "heredity and heredity" are pitted 

 against each other in his thinking, quite in the spirit 

 of the logic of chance. 



The question is so important, and at the same time 

 so complex and obscure, that we had better make a 

 fresh heading for it. 



II 



We have to ask then whether there is a special 

 appeal to chance by Darwin in his doctrine of 

 variations ? 



Darwin largely treated these as casual, almost as 

 if uncaused. But it was not, for the moment, his 

 affair to say how variations arose ; he was to show 

 how they worked out. He never thought of assert- 

 ing deliberately that variations are uncaused; his 

 followers explicitly deny and repudiate any such 

 view. 



