57% 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 réle in the relation of the sexes to each other 
may be freely admitted. In other words, in some animals the 
