XXV] 



DARWIN 



19 



certain extent^ be useful to the male seems to me quite un- 

 sound, and directly opposed to your own doctrine so con- 

 vincingly urged in the ' Origin/ that natural selection never 

 improves an animal beyond its needs. Admitting, therefore, 

 abundant variation of colour in both sexes, it is impossible 

 that the male can be brought by natural selection to 

 resemble the female (unless such variations are always 

 transmitted), because the difference in their colours is for 

 the purpose of making up for their different organization 

 and habits, and natural selection cannot give to the male 

 more protection than he requires, which is less than in the 

 female. 



" 5. The striking fact that in all protected groups the females 

 usually resemble the males (or are equally brightly coloured) 

 shows that the usual tendency is to transmit colour to both 

 sexes when it is not injurious to either. 



" Now for the special argument. 



*'6. In the very weak-flying Leptalis both sexes mimic 

 Heliconidae. But in the much stronger-flying Papilio, Pieris, 

 and Diadema, it is the female only that mimics the protected 

 group, and in these cases the females often acquire brighter 

 and more conspicuous colours than the male. 



" 7. No case is known of a male Papilio, Pieris, or Diadema, 

 alone, mimicking a protected species ; yet colour is more 

 frequent in males, and variations are always ready for the 

 purpose of sexual or other forms of selection. 



" 8. The fair inference seems to be that each species^ and 

 also each sex^ can only be modified by selection just as far 

 as is absolutely necessary — not a step further. A male, 

 being by structure and habits less exposed to danger, and 

 therefore requiring less protection than the female, cannot 

 have an equal amount of protection given to it by natural 

 selection ; but the female must have some extra protection to 

 balance her greater exposure to danger, and she rapidly 

 acquires it in one way or another. 



" 9. The objection as to male fish, which seem to require 

 protection, yet have sometimes bright colours, seems to me 

 of no more weight than is the existence of some unprotected 



