492 THE DESCENT OP MAN. 



turity, or they assume it only during tlie breeding-season, or 

 the tints then become more vivid. Certain ornamental appen- 

 dages become enlarged, turgid, and brightly colored during the 

 act of courtship. The males display their charms with elaborate 

 care and to the best effect; and this is done in the presence of 

 the females. The courtship is sometimes a prolonged affair, and 

 many males and females congregate at an appointed place. To 

 suppose that the females do not appreciate th« beauty of the 

 males, Is to admit that their splendid decorations, all their pomp 

 and display, are useless; and this is incredible. Birds have fine 

 powers of discrimination, and in some few instances it can be 

 shown that they have a taste for the beautiful. The females, 

 moreover, are known occasionally to exhibit a marked preference 

 or antipathy for certain individual males. 



If it be admitted that the females prefer, or are unconsciously 

 excited by the more beautiful males, then the males would slowly 

 but surely be rendered more and more attractive through sexual 

 selection. That it is this sex which has been chiefly modified, 

 we may infer from the fact that, in almost every genus where 

 the sexes differ, the males differ much more from one another 

 than do the females; this is well shown in certain closely- allied 

 representative species, in which the females can hardly be distin- 

 guished, whilst the males are quite distinct. Birds in a state of na- 

 ture offer individual differences which would amply suffice for the 

 work of sexual selection; but we have seen that they occasionally 

 present more strongly-marked variations which recur so frequent- 

 ly that they would immediately be fixed, if they served to allure 

 the female. The laws of variation must determine the nature of the 

 initial changes, and will have largely influenced the final result. 

 The gradations, which may be observed between the )nales of 

 allied species, Indicate the nature of the steps through which 

 they have passed. They explain also in the most interesting man- 

 ner how certain characters have originated, such as the Indented 

 ocelli on the tail-feathers of the peacock, and the ball and socket 

 ocelli on the wing-feathers of the Argus pheasant. It is evident 

 that the brilliant colors, top-knots, fine plumes, &c., of. many 

 male birds cannot have been acquired as a protection; Indeed, 

 they sometimes lead to danger. That they are not due to the 

 direct and definite action of the conditions of life, we may feel 

 assured, because the females have been exposed to the same con- 

 ditions, and yet often differ from the males to an extreme degree. 

 Although it is probable that changed conditions acting during a 

 lengthened period have in some cases produced a definite effect 

 on both sexes, or sometimes on one sex alone, the more important 

 result will have been an increased tendency to vary or to present 

 more strongly marked individual differences; and such diflier- 



