1863.] MR. BENTHAM. 25 



benefit, is it so very wonderful that some forms should change 

 much slower and much less, and some few should have 

 changed not at all under conditions which to us (who really 

 know nothing what are the important conditions) seem very 

 different. Certainly a priori we might have anticipated that 

 all the plants anciently introduced into Australia would have 

 undergone some modification ; but the fact that they have 

 not been modified does not seem to me a difficulty of weight 

 enough to shake a belief grounded on other arguments. I 

 have expressed myself miserably, but I am far from well 

 to-day. 



I am very glad that you are going to allude to Pasteur ; I 

 was struck with infinite admiration at his work. With cordial 

 thanks, believe me, dear Bentham, 



Yours very sincerely, 



Ch. Darwin. 



P.S. — In fact the belief in Natural Selection must at present 

 be grounded entirely on general considerations. (1) On its 

 being a vera causa, from the struggle for existence ; and the 

 certain geological fact that species do somehow change. (2) 

 From the analogy of change under domestication by man's 

 selection. (3) And chiefly from this view connecting under 

 an intelligible point of view a host of facts. When we descend 

 to details, we can prove that no one species has changed 

 [i.e. we cannot prove that a single species has changed] ; 

 nor can we prove that the supposed changes are beneficial, 

 which is the groundwork of the theory. Nor can we 

 explain why some species have changed and others have 

 not. The latter case seems to me hardly more difficult to 

 understand precisely and in detail than the former case of 

 supposed change. Bronn may ask in vain, the old creationist 

 school and the new school, why one mouse has longer ears 

 than another mouse, and one plant more pointed leaves than 

 another plant. 



