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.” 
