GENEUAL SUMMARY AND CONCLUSION. 703 



which they shall be developed. It appears that variations 

 arising late in life are commonly transmitted to one and 

 the same sex. Variability is the necessary basis for the 

 action of selection and is wholly independent of it. It fol- 

 lows from this, that variations of the same general nature 

 have often been taken advantage of and accumulated 

 through sexual selection in relation to the propagation of 

 the species, as well as through natural selection in relation 

 to the general purposes of life. Hence secondary sexual 

 characters, when equally transmitted to both sexes, can be 

 distinguished from ordinary specific characters only by the 

 light of analogy. The modifications acquired through 

 sexual selection are often so strongly pronounced that the 

 two sexes have frequently been ranked as distinct species, 

 or even as distinct genera. Such strongly marked differ- 

 ences must be in some manner highly important; and we 

 know that they have been acquired in some instances at 

 the cost not only of inconvenience, but of exposure to 

 actual danger. 



The belief in the power of sexual selection rests chiefly 

 on the following considerations. Certain characters are 

 confined to one sex; and this alone renders it probable that 

 in most cases they are connected with the act of reproduc- 

 tion. In innumerable instances these characters are fully 

 developed only at maturity, and often during only a part of 

 the year, which is always the breeding- season. The males 

 (passing over a few exceptional cases) are the more active 

 in courtship; they are the better armed, and are rendered 

 the more attractive in various ways. It is to be especially 

 observed that the males display their attractions with 

 elaborate care in the presence of the females; and that 

 they rarely or never display them excepting during the 

 season of love. It is incredible that all this should be pur- 

 poseless. Lastly, we have distinct evidence with some 

 quadrupeds and birds that the individuals of one sex are 

 capable of feeling a strong antipathy or preference for 

 certain individuals of the other sex. 



Bearing in mind these facts and the marked results of 

 man's unconscious selection when applied to domesticated 

 animals and cultivated plants it seems to me almost cer- 

 tain that if the individuals of one sex were during a long 

 series of generations to prefer pairing with certain indi- 

 viduals pi the other sex^ characterized in some peculiar 



