112 THE 'ORIGIN OF SPECIES.' [1860. 



structures. I have stated in my volume that it is hardly 

 possible to know which, /*. e. whether instinct or structure, 

 change first by insensible steps. Probably sometimes in- 

 stinct, sometimes structure. When a British insect feeds on 

 an exotic plant, instinct has changed by very small steps, and 

 their structures might change so as to fully profit by the new 

 food. Or structure might change first, as the direction of 

 tusks in one variety of Indian elephants, which leads it to 

 attack the tiger in a different manner from other kinds of 

 elephants. Thanks for your letter of the 2nd, chiefly about 

 Murray. (N.B. Harvey of Dublin gives me, in a letter, the 

 argument of tall men marrying short women, as one of great 

 weight ! *) 



I do not quite understand what you mean by saying, " that 

 the more they prove that you underrate physical conditions, 

 the better for you, as Geology comes in to your aid." 



... I see in Murray and many others one incessant fal- 

 lacy, when alluding to slight differences of physical conditions 

 as being very important ; namely, oblivion of the fact that all 

 species, except very local ones, range over a considerable 

 area, and though exposed to what the world calls considerable 

 diversities, yet keep constant. I have just alluded to this in 

 the ' Origin ' in comparing the productions of the Old and 

 the New Worlds. Farewell, shall you be at Oxford ? If H. 

 gets quite well, perhaps I shall go there. 



Yours affectionately, 



C. DARWIN. 



C. Darwin to C. LyclL 



Down [June I4th, 1860]. 



. . . Lowell's review \ is pleasantly written, but it is clear 

 that he is not a naturalist. He quite overlooks the impor- 

 tance of the accumulation of mere individual differences, and 

 which, I think I can show, is the great agency of change 



* See footnote, ante, p. 56. 



f J. A. Lowell in the ' Christian Examiner/ May 1860. 



