276 WORK ON ' MAN.' [1867 



C. Darwin to A. R. Wallace. 



Down, February 26 [1867]. 



MY DEAR WALLACE, Bates was quite right ; you are the 

 man to apply to in a difficulty. I never heard anything more 

 ingenious than your suggestion,* and I hope you may be able 

 to prove it true. That is a splendid fact about the white 

 moths ; it warms one's very blood to see a theory thus almost 

 proved to be true.f With respect to the beauty of male but- 

 terflies, I must as yet think that it is due to sexual selection. 

 There is some evidence that dragon-flies are attracted by 

 bright colours ; but what leads me to the above belief is, so 

 many male Orthoptera and Cicadas having musical instru- 

 ments. This being the case, the analogy of birds makes me 

 believe in sexual selection with respect to colour in insects. 

 I wish I had strength and time to make some of the experi- 

 ments suggested by you, but I thought butterflies would not 

 pair in confinement. I am sure I have heard of some such 

 difficulty. Many years ago I had a dragon-fly painted with 

 gorgeous colours, but I never had an opportunity of fairly 

 trying it. 



The reason of my being so much interested just at present 

 about sexual selection is, that I have almost resolved to 

 publish a little essay on the origin of Mankind, and I still 

 strongly think (though I failed to convince you, and this, to 

 me, is the heaviest blow possible) that sexual selection has 

 been the main agent in forming the races of man. 



By the way, there is another subject which I shall intro- 

 duce in my essay, namely, expression of countenance. Now, 



* The suggestion that conspicuous caterpillars or perfect insects (e. g. 

 white butterflies), which are distasteful to birds, are protected by being 

 easily recognised and avoided. See Mr. Wallace's ' Natural Selection,' 

 2nd edit., p. 117. 



f Mr. Jenner Weir's observations published in the Transactions of the 

 Entomolog. Soc. (1869 and 1870) give strong support to the theory in 

 question. 



