SEXUAL SELECTION 63 



In the first place, we have to notice the presence of 

 special weapons, such as horns or tusks, developed 

 exclusively or to a special extent in the males of 

 those species in which it is the habit of the members 

 of this sex to strive together for the possession of the 

 females. In such cases the stronger and better-armed 

 males are supposed to survive, and to leave a greater 

 number of offspring than their weaker rivals ^ so that 

 this form of competition is regarded as acting in 

 quite a similar way to natural selection. 



In a second set of cases, of which many remarkable 

 instances are to be seen among birds, the males are 

 found to exhibit brilliant and varied colours, or to 

 possess special decorations in the form of plumes or 

 other appendages, or to be gifted with the power of 

 song. It is to cases such as these that the term sexual 

 selection more properly applies* since the females are 

 supposed to bestow their favours upon the most 

 beautiful males, and to reject the advances of those 

 among their suitors which are less lavishly provided 

 with ornament. 



In these cases, where the development of brilliant 

 colours or other ornamental arrangements is believed 

 to have taken place owing to the choice of the females 

 particularly in such a case as is represented by the 

 peacock's tail or the wings of the Argus pheasant- 

 the supposed change must have come about in direct 

 opposition to the action of natural selection, since the 

 latter would favour a production of colours resembling 

 those of the natural environment for the sake of con- 

 cealment, and would hinder the formation of such 



