334 THE COLOURS OF ANIMALS 



the front, while they become invisible from the side 

 or from behind, for the colour is produced in such a 

 way as to give the female the best chance of seeing it, 

 a fact which is unexplained by any other theory of 

 origin except that of Sexual Selection. At the same 

 time this observation needs testing by further and 

 exact observation of the habits of many iridescent 

 species during courtship. 



The evidence for the gradual development of pattern 

 suggests selective breeding 



The steps by which some of the most elaborate and 

 wonderful appearances have arisen, are traced by Mr. 

 Darwin in the most complete and convincing manner. 

 When we look at the marvellous eyes upon the train of a 

 Peacock, or the more beautiful markings on the feathers 

 of the male Argus Pheasant, it seems impossible that so 

 wonderful and complete a result can have been produced 

 by the aesthetic preferences of female birds. And yet Mr. 

 Darwin shows the relation between these characters and 

 much simpler markings on other parts of the surface. 

 He proves that the one has been derived from the other 

 by gradual modification, and he points to traces of 

 the original marking which persist in the complex 

 appearance to which it has given rise. Such facts, 

 while eminently suggestive of the progressive develop- 

 ment of simple into complex markings by some 

 selective agency, seem to be unexplained by any other 



