1867.] SEXUAL SELECTION. 93 



paradise, humming-birds, the Rupicola, or any other such 

 cases? Many gallinaceous birds certainly are polygamous. 

 I suppose that birds may be known not to be polygamous 

 if they are seen during the whole breeding season to asso- 

 ciate in pairs, or if the male incubates or aids in feeding 

 the young. Will you have the kindness to turn this in your 

 mind ? But it is a shame to trouble you now that, as I am 

 heartily glad to hear, you are at work on your Malayan 

 travels. I am fearfully puzzled how far to extend your 

 protective views with respect to the females in various 

 classes. The more I work, the more important sexual 

 selection apparently comes out. 



Can butterflies be polygamous ? i.e. will one male impreg- 

 nate more than one female ? Forgive me troubling you, and 

 I dare say I shall have to ask forgiveness again. . . . 



C. Darwin to A. R. Wallace. 



Down, 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 cater- 

 pillars 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 caterpillar he ever 

 saw in Amazonia (of a sphinx) was conspicuous at the 

 distance of yards, from its black and red colours, whilst 

 feeding on large green leaves. If any one objected to male 

 butterflies having been made beautiful by sexual selection, 

 and asked why should they not have been made beautiful as 



