170 'DESCENT OF MAN' — EXPRESSION. [1872. 



anything more original and interesting than your treatment 

 of the causes which favour the development of scientific men. 

 The whole was quite new to me, and most curious. When 

 I began your essay I was afraid that you were going to attack 

 the principle of inheritance in relation to mind, but I soon 

 found myself fully content to follow you and accept your 

 limitations. I have felt, of course, special interest in the 

 latter part of your work, but there was here less novelty to 

 me. In many parts you do me much honour, and every- 

 where more than justice. Authors generally like to hear what 

 points most strike different readers, so I will mention that of 

 your shorter essays, that on the future prevalence of lan- 

 guages, and on vaccination interested me the most, as, indeed, 

 did that on statistics, and free will. Great liability to certain 

 diseases, being probably liable to atavism, is quite a new idea 

 to me. At p. 322 you suggest that a young swallow ought to 

 be separated, and then let loose in order to test the power 

 of instinct ; but nature annually performs this experiment, 

 as old cuckoos migrate in England some weeks before the 

 young birds of the same year. By the way, I have just used 

 the forbidden word " nature," which, after reading your 

 essay, I almost determined never to use again. There 

 are very few remarks in your book to which I demur, but 

 when you back up Asa Gray in saying that all instincts are 

 congenital habits, I must protest. 



Finally, will you permit me to ask you a question : have 

 you yourself, or [has] some one who can be quite trusted, 

 observed (p. 322) that the butterflies on the Alps are tamer 

 than those on the lowlands ? Do they belong to the same 

 species ? Has this fact been observed with more than one 

 species ? Are they brightly coloured kinds ? I am especially 

 curious about their alighting on the brightly coloured parts 

 of ladies' dresses, more especially because I have been more 

 than once assured that butterflies like bright colours, for 

 instance, in India the scarlet leaves of Pointsettia. 



