:J36 THE evolution theory 



sexual .selection, and that in the production of a protective colouring 

 it is a ([uestion of deceiving the e3'e of a sharp-sighted enemy, while 

 thf nini of sexual selection is to secure the approval of others of the 

 same species. As long as the enemy on the search for prey perceives 

 the diftorence between the markings of its victim and tlio.se of the 

 surroundings, .so long will the gradual and steady improvement of the 

 protective coloration continue, so long will new shades and new lines 

 be added. We can thus understand how there would be gradually 

 reached a complexity of marking to which sexual selection can never 

 attain, or at least only in regard to a few specially favourable points. 

 'Vhv eye-spots on the train feathers of the Argus pheasant and the 

 peacock are such points, and these occur among polygamous birds 

 in which sexual selection must be very intense ; they are placed, too, 

 on a part of the body, the wheel-shaped train, which is peculiarly 

 suited for communicating the excitement of the male to the female, 

 and must therefore be especially influenced by the latter. In general, 

 however, we may say on a priori grounds that the intensity of 

 species-selection is greater than that of sexual selection, because the 

 former ceaselessly and pitilessly eliminates the less perfect, while the 

 claims of the latter are in any case less imperative, and are also 

 often mollified by a variety of chance circumstances. 



But in the case of insects, in particular, we have to add that the 

 protective colours and the decorative colours have been, .so to speak, 

 painted by different artists — the former by birds, lizards, and other 

 persecutors endowed with well - developed eyes, the latter by the 

 insects themselves, whose eyes can hardly possess, for objects not 

 quite near, that acuteness of vision which the bird's eye has. Thus 

 we find that the protective coloration of butterflies has often a very 

 complex marking, while the same butterfly may exhibit onl}^ a rather 

 crude though brilliant pattern on its upper surface, where the 

 coloration is due to sexual selection. Thus the famous KaU'tina has 

 on its under surface the likeness of a dry or decayed leaf composed of 

 a number of colour-tones — quite a complex painting. But if we look 

 at the upper surface we see a deep brown with a shimmer of steel 

 blue as the ground-colour of the wings, and on it a broad yellow band 

 and a white spot : that is the whole pattern. We find a similar state 

 of things among many of the forest buttei-flies of Brazil, and also 

 among our indigenous butterflies. The pattern of our gayest diurnal 

 butterflies, the red Admiral and the tortoiseshell butterfly [Vanessa 

 atalanta and Vanessa cardui), is somewhat crude on the upper surface, 

 and ver}^ simple compared with the protective colouring of the under 

 surface, which is made up of hundreds of points, spots, strokes, and 



