My dear Sir

I began reading yr new book sooner than I intended, & when I once began, I c^d not stop; & now you must allow me to thank you for the very great pleasure which it has given me.¹ I have hardly ever read any thing more original & interesting than your treatment of the causes which favour the development of scientific men.² The whole was quite new to me, & most curious. When I began yr 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 & accept your limitations.³ 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, & every where more than justice.⁴ 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 languages & on vaccination interested me the most, as indeed did that on statistics & free-will. Great liability to certain diseases being probably liable to atavism is quite a new idea to me.⁵ At p. 322 you suggest that a young swallow ought to be separated & then let loose in order to test the power of instinct; but nature annually performs this experiment, as old cuckoos migrate in England, & I presume elswhere, 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.⁶ There are very few remarks in yr book to which I demur; but when you back up Asa Gray in saying that all instincts are congenital habits, I must protest.⁷ Finally, will you permit me to ask you a question: have you yourself, or 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 scarlett leaves of Pointsettia.⁸

Once again allow me thank you for having sent me your work, & for the very unusual amount of pleasure which I have received in reading it.

With much respect I remain, my dear Sir | yours very sincerely | Charles Darwin