190 Evolution and Adaptation 



Darwin is inclined to adopt this view, that those males that 

 make the most noise will be more likely to be heard, and 

 possibly approached. They will, therefore, be more likely to 

 leave descendants. We have already considered this question 

 when dealing with the theory of natural selection in the pre- 

 ceding chapter and need not go over the ground again. This 

 much may, however, be said again, that even if it is probable 

 that these organs are of use to the animals in finding each 

 other, and this seems not improbable, it does not follow that 

 the organs have been acquired through selection for this 

 purpose. 



Darwin finds his best examples of secondary sexual charac- 

 ters in the group of vertebrates, and since in this group the 

 intelligence is of a higher order than in the other groups, the 

 argument that the female chooses the more pleasing suitor is 

 made to appear more plausible. 



The elongation of the lower jaw that occurs in a few fishes 

 at the breeding season is regarded as a secondary sexual 

 character. On the other hand, Darwin recognizes the follow- 

 ing difficulty in regard to the size of the males : — 



" In regard to size, M. Carbonnier maintains that the 

 female of almost all fishes is larger than the male ; and Dr. 

 Giinther does not know of a single instance in which the 

 male is actually larger than the female. With some cyprino- 

 donts the male is not even half as large. As in many kinds 

 of fishes the males habitually fight together, it is surprising 

 that they have not generally become larger and stronger than 

 the females through the effects of sexual selection. The 

 males suffer from their small size, for, according to M. Car- 

 bonnier, they are liable to be devoured by the females of 

 their own species when carnivorous, and no doubt by other 

 species. Increased size must be in some manner of more 

 importance to the females, than strength and size are to the 

 males for fighting with other males ; and this perhaps is to 

 allow of the production of a vast number of ova." 



