37 2 Evolution and Adaptation 



ments seem to demand. The exact symmetry of many forms 

 appears in some cases to be unnecessarily perfect. The per- 

 fection of the hand of man, the development of his vocal 

 organs, and certain qualities of his brain, as his musical and 

 mathematical powers, seem to go beyond the required limits. 

 It is not, of course, that these things may not be of some use, 

 but that their development appears to have gone beyond what 

 selection requires of these parts. 



Closely related to this group of phenomena are those cases 

 in which certain organs are well developed, but which can 

 scarcely be of use to the animal in proportion to their elabo- 

 ration. The electric organs of several fishes and skates are 

 excellent examples of this sort of structures. The phospho- 

 rescent organs do not appear, in some forms at least, to be 

 useful in proportion to their development. The selection 

 theory fails completely to explain the building up of organs 

 of this kind, but on the mutation theory there is no difficulty 

 at all in accounting for the presence of even highly developed 

 organs that are of little or of no use to the individual. If the 

 organs appeared in the first place as mutations, and their 

 presence was not injurious to the extent of interfering seri- 

 ously with the existence and propagation of the new form, 

 this new form may remain in existence, and if the mutations 

 continued in the same direction, the organs might become 

 more perfect, and highly developed. The whole class of sec- 

 ondary sexual organs may belong to this category, but a discus- 

 sion of these organs will be deferred to the following section. 



Secondary Sexual Organs as Adaptations 



In the sixth chapter we have examined at some length Dar- 

 win's interpretation of the secondary sexual characters. 

 His explanation has been found insufficient in many cases to 

 account for the conditions. That these organs do play in 

 some cases a role in the relation of the sexes to each other 

 may be freely admitted. In other words, in some animals the 



