Alfred Russel Wallace 



DowUy Bromley, Kent, 8.E. February 23, 1867. 



Dear Wallace, — I much regretted that I was unable to 

 call on you, but after Monday I was unable even to leave 

 the house. On Monday evening I called on Bates and put 

 a difficulty before him, which he could not answer, and, 

 as on some former similar occasion, his first suggestion 

 was, ^^ You had better ask Wallace." My difficulty is, why 

 are caterpillars sometimes so beautifully and artistically 

 coloured ? Seeing that many are coloured to escape danger, 

 I can hardly attribute their bright colour in other cases to 

 mere physical conditions. Bates says the most gaudy cater- 

 pillar he ever saw in Amazonia (of a Sphinx) was con- 

 spicuous at the distance of yards from its black and red 

 colouring whilst feeding on large green leaves. If anyone 

 objected to male butterflies having been made beautiful by 

 sexual selection, and asked why should they not have been 

 made beautiful as well as their caterpillars, what would 

 you answer ? I could not answer, but should maintain 

 my ground. Will you think over this, and some time, 

 either by letter or when we meet, tell me what you think ? 

 Also, I want to know whether your female mimetic butter- 

 fly is more beautiful and brighter than the male ? 



When next in London I must get you to show me your 

 Kingfishers. 



My health is a dreadful evil ; I failed in half my engage- 

 ments during this last visit to London. — Believe me, yours 

 very sincerely, C. Darwin. 



The answer to this letter is missing, but in Vol. II. of 

 '' My Life," p. 3, Wallace writes : 



^' On reading this letter I almost at once saw Vrhat 

 seemed to be a very easy and probable explanation of the 

 facts. I had then just been preparing for publication (in 

 the Westminster Review) my rather elaborate paper on 



178 



