SEXUAL SELECTION 353 



due to the unchecked growth of such characters, as they appear, 

 apparently fortuitously, in the germ plasm. They are a by- 

 product of sexual selection, in the sense that they of necessity 

 take part in the sexual demonstrations of the desire to mate. 

 Sexual selection is answerable for the display, inasmuch as the 

 most demonstrative birds have the best, and possibly the only, 

 chance of securing a mate. But neither the brilliant colours 

 nor the excessive development of feathers in this or that area, 

 e.g., the wing feathers of the Argus Pheasant, the long streamers 

 of certain Birds of Paradise, can be attributed to this cause. 

 These are germinal variations which have survived, and may 

 have attained exaggerated proportions, because they formed no 

 obstacle to the struggle for existence, and in this they re- 

 semble all other fortuitous variations. They are no more 

 the result of sexual selection than are the characteristic antics 

 of say the Kagu, Sun-bird, Great Bustard, which appear to be 

 unique. This contention seems to be borne out by the fact 

 that birds of the most sober hues affect displays of a character 

 precisely similar in kind to those of birds in which this display 

 appears to be made for the sole purpose of exhibiting to the 

 best advantage some specially modified or beautifully coloured 

 feathers. 



There can be no tradition among birds in the matter of 

 display; no means by which each new generation can compare 

 the standard of perfection of that which preceded it. And this 

 being so, the slow increments made by each generation cannot 

 be appreciated. These secondary sexual characters, like other 

 physical characters, pursue their development in spite of and 

 not because of sexual selection. Their only controlling factor 

 is natural selection. All that sexual selection does is to insist 

 on a display of some sort, accompanied or not, as the case may 

 be, by " embroidery ". Undemonstrative birds die without 

 offspring. Generally, of course, a non-demonstrating bird is so 

 because of a lack of virility, and their failure to mate preserves 

 the vigour of the race. 



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