1872.] ISOLATION. 157 



very few naturalists believe in this. I may have erred on 

 many points, and extended the doctrine too far, but I feel a 

 strong; conviction that sexual selection will hereafter be 

 admitted to be a powerful agency. I cannot agree with what 

 you say about the taste for beauty in animals not easily vary- 

 ing. It may be suspected that even the habit of viewing 

 differently coloured surrounding objects would influence their 

 taste, and Fritz Miiller even goes so far as to believe that the 

 sight of gaudy butterflies might influence the taste of distinct 

 species. There are many remarks and statements in your 

 essay which have interested me greatly, and I thank you for 

 the pleasure which I have received from reading it. 

 With sincere respect, I remain, 



My dear Sir, yours very faithfully, 



Charles Darwin. 



P.S. — If you should ever be induced to consider the whole 

 doctrine of sexual selection, I think that you will be led to 

 the conclusion, that characters thus gained by one sex are 

 very commonly transferred in a greater or less degree to the 

 other sex. 



[With regard to Moritz Wagner's first Essay, my father 

 wrote to that naturalist, apparently in 1868 :] 



Dear and respected Sir, — I thank you sincerely for 

 sending me your ' Migrationsgesetz, &c.,' and for the very 

 kind and most honourable notice which you have taken of my 

 works. That a naturalist who has travelled into so many and 

 such distant regions, and who has studied animals of so many 

 classes, should, to a considerable extent, agree with me, is, I 

 can assure you, the highest gratification of which I am 

 capable. . . . Although I saw the effects of isolation in the 

 case of islands and mountain-ranges, and knew of a few 

 instances of rivers, yet the greater number of your facts were 

 quite unknown to me. I now see that from the want of 



