ASA GRAY. 117 



use to which the fragments may be put, their shape may be 

 strictly said to be accidental. . . ." 



In his article in the Nation (March 19th, 1868), 

 Asa Gray criticised the metaphor as follows : 



" But in Mr. Darwin's parallel, to meet the case of nature 

 according to his own view of it, not only the fragments of 

 rock (answering to variation) should fall, but the edifice 

 (answering to natural selection) should rise, irrespective of will 

 or choice ! " 



This passage is quoted in the " Life and Letters " 

 (Vol. III., p. 84), and Francis Darwin makes the 

 convincing reply : 



" But my father's parallel demands that natural selection 

 shall be the architect, not the edificethe question of design 

 only comes in with regard to the form of the building 

 materials." 



Darwin's reply was contained in his letter to 

 Asa Gray dated May 8th, 1868 : 



"You give a good slap at my concluding metaphor": un- 

 doubtedly I ought to have brought in and contrasted natural 

 and artificial selection ; but it seemed so obvious to me that 

 natural selection depended on contingences even more complex 

 than those which must have determined the shape of each frag- 

 ment at the base of my precipice. What I wanted to show was 

 that, in reference to pre-ordainment, whatever holds good in 

 the formation of an English pouter-pigeon holds good in the 

 formation of a natural species of pigeon. I cannot see that 

 this is false. If the right variations occurred, and no others, 

 natural selection would be superfluous." 



To this, Asa Gray replied in his letter of May 

 25th : 



