200 TROPICAL NATURE, AND OTHER ESSAYS. 



evidence collected by Mr. Darwin himself proves that 

 each bird finds a mate under any circumstances. He 

 gives a number of cases of one of a pair of birds being 

 shot, and the survivor being always found paired again 

 almost immediately. This is sufficiently explained on 

 the assumption that the destruction of birds by various 

 causes is continually leaving widows and widowers in 

 nearly equal proportions, and thus each one finds a fresh 

 mate ; and it leads to the conclusion that permanently 

 unpaired birds are very scarce ; so that, speaking broadly, 

 every bird finds a mate and breeds. But this would 

 almost or quite neutralize any effect of sexual selection 

 of colour or ornament, since the less highly-coloured birds 

 would be at no disadvantage as regards leaving healthy 

 offspring. If, however, heightened colour is correlated 

 with health and vigour ; and if these healthy and vigorous 

 birds provide best for their young, and leave offspring 

 which, being equally healthy and vigorous, can best 

 provide for themselves which cannot be denied ; then 

 natural selection becomes a preserver and intensifier 

 of colour. 



Another most important consideration is, that male 

 butterflies rival or even excel the most gorgeous male 

 birds in bright colours and elegant patterns ; and among 

 these there is literally not one particle of evidence that 

 the female is influenced by colour, or even that she has 

 any power of choice; while there is much direct evidence 

 to the contrary (Descent of Man, p. 318). The weak- 

 ness of the evidence for conscious sexual selection among 

 these insects is so palpable, that Mr. Darwin is obliged 

 to supplement it by the singularly inconclusive argument 

 that, " Unless the female prefer one male to another, the 



