NATURAL SELECTION; SEXUAL SELECTION 77 



many males sing, or dance, or otherwise draw to themselves 

 the attention of the females. Seventh, the secondary sexual 

 characters are especially variable. Darwin believed that he 

 had observed certain other conditions to exist which helped 

 make the sexual selection theory probable, but the conditions 

 noted are sufficient if they are real. 



Exposed to careful scrutiny and criticism, the theory of 

 sexual selection has been relieved of all necessity of explaining 

 any but two categories of secondary sexual characters; namely, 

 the special weapons borne by males, and special ornaments and 

 excitatory organs of the males and females. For examination 

 has disclosed the fact that males are not alone in the possession 

 of special characters of attraction or excitation. Regarding 

 these two categories Plate in his able recent defense of Darwinism, 

 says "the first part of this theory, the origin of the special 

 defensive and offensive weapons of males through sexual selec- 

 tion, is nearly universally accepted. The second part of the 

 theory, the origin of exciting organs, has given rise to much 

 controversy. Undoubtedly the presumption that the females 

 compare the males and then choose only those which have the 

 most attractive colors, the finest song, or the most agreeable 

 odor, presents great difficulties, but it is doubtful if it is possible 

 to replace this explanation by a better." Some of these diffi- 

 culties may be briefly enumerated. 



The theory can be applied only to species in which the 

 males are markedly more numerous than the females, or in which 

 the males are polygamous. In other cases there will be a female 

 for each male whether he be ornamented or not; and the unor- 

 namented males can leave as many progeny as the ornamented 

 ones, which would prevent any accumulation of ornamental 

 variations by selection. As a matter of fact, in a majority of 

 animal species, especially of the higher vertebrates, males and 

 females exist in approximately equal numbers. 



Observation shows that in most species the female is wholly 

 passive in the matter of pairing, accepting the first male that 

 offers. Note the cock and hens in the barnyard, or the fur seal 

 in the rookeries. 



Ornamental colors are as often a characteristic of males of 

 kinds of animals in which there is no real pairing, as among 

 those which pair. How explain by sexual selection the remark- 

 able colors in the breeding season of many fishes, in which the 



