236 THE DESCENT OF MAN. 



sively in this line, ttiey would be extremely liable to be lost. If, 

 however, the females varied and submitted their newly acquired 

 characters to their offsprings of both sexes, the characters which 

 were advantageous to the males would be preserved by them 

 through sexual selection, and the two sexes would in consequence 

 be modified in the same manner, although such characters were 

 of no use to the females; but I shall hereafter have to recur to 

 these more intricate contingencies. Lastly, the females may ac- 

 quire, and apparently have often acquired by transference, char- 

 acters from the male sex. 



As variations occurring late in life, and transmitted to one sex 

 alone, have incessantly been taken advantage of and accumulated 

 through sexual selection in relation to the reproduction of the 

 species; therefore it appears, at first sight, an unaccountable fact 

 that similar variations have not frequently been accumulated 

 through natural selection, in relation to the ordinary habits of life. 

 If this had occurred, the two sexes would often have been differ- 

 ently modified, for the sake, for instance, of capturing prey or of 

 escaping from danger. Differences of this kind between the two 

 sexes do occasionally occur, especially in the lower classes. But 

 this implies that the two sexes follow different habits in their 

 struggles for existence, which is a rare circumstance with the 

 higher animals. The case, however, is widely different with the 

 reproductive functions, in which respect the sexes necessarily dif- 

 fer. For variations in structure which are related to these func- 

 tions, have often proved of value to one sex, and from having 

 arisen at a late period of life, have been transmitted to one sex 

 alone; and such variations, thus preserved and transmitted, 

 have given rise to secondary sexual characters. 



In the following chapters, I shall treat of the secondary sexual 

 characters in animals of all classes, and shall endeavor in each 

 case to apply the principles explained in the present chapter. The 

 lowest classes will detain us for a very short time, but the higher 

 animals, especially birds, must be treated at considerable length. 

 It should be borne in mind that for reasons already assigned, I 

 intend to give only a few illustrative instances of the innumerable 

 structures by the aid of which the male finds the female, or when 

 found, holds her. On the other hand, all structures and instincts 

 by the aid of which the male conquers other males, and by whicn 

 he allures or excites the female, will be fully discussed, as these 

 are in many ways the most interesting. 



Supplement on the proportional numbers of the two sexes vn an- 

 imals belonging to various classes 



As no one, as far as I can discover, has paid attention to the 

 relative numbers of the two sexes throughout the animal king- 



