154 NATURAL SELECTION vn 

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also in the forms given to living organisms " (Reign of Law, 

 p. 248). 



Here the statement that " no connection can be conceived 

 between the splendour of the humming birds and any function 

 essential to their life," is met by the fact that Mr. Darwin 

 has not only conceived but has shown, both by observation 

 and reasoning, how beauty of colour and form may have a 

 direct influence on the most important of all the functions of 

 life, that of reproduction. In the variations to which birds 

 are subject, any more brilliant colour than usual is believed 

 to be attractive to the females, and would therefore lead to 

 the individuals so adorned leaving more than the average 

 number of offspring. There are some indications that this kind 

 of sexual selection does actually take place, and the laws of 

 inheritance would necessarily lead to the further development 

 of any individual peculiarity that was attractive, and thus the 

 splendour of the humming birds is directly connected with 

 their very existence. It is true that "a crest of topaz may 

 be no better than a crest of sapphire," but either of these may 

 be much better than no crest at all ; and the different condi- 

 tions under which the parent form must have existed in 

 different parts of its range will have determined different 

 variations of tint, either of which were advantageous. 1 The 

 reason why female birds are not adorned with equally brilliant 

 plumes is sufficiently clear ; they would be injurious by ren- 

 dering their possessors too conspicuous during incubation. 

 Survival of the fittest has therefore favoured the development 

 of those dark green tints on the upper surface of so many 

 female humming birds, which are most conducive to their 

 protection while the important functions of hatching and 

 rearing the young are being carried on. Keeping in mind 

 the laws of multiplication, variation, and survival of the 

 fittest, which are for ever in action, these varied develop- 



1 Since writing this essay I have come to the conclusion that mere 

 diversity of colouring between species is an important factor in their differ- 

 entiation, serving as a means of recognition, and thus preventing cross- 

 unions. See Damnnism, p. 217. I have also been led to doubt the reality 

 of the fact of female selection of slight differences of colour on which Mr. 

 Darwin relied, but it has not been thought advisable to alter the passages 

 which seem to admit it, as they represent my belief at the time they were 



