Chap. XV. SEXUALLY LIMITED INHERITANCE. 161 



young, such variations would be of no service until tlie 

 age for reproduction had arrived, and there was compe- 

 tition between rival males. But in the case of birds 

 which live on the ground and which commonly need 

 the protection of dull colours, bright tints would be far 

 more dangerous to the young and inexperienced than 

 to the adult males. Consequently the males which 

 varied in brightness whilst young would suffer much 

 destruction and be eliminated through natural selec- 

 tion ; on the other hand the males which varied in 

 this manner when nearly mature, notwithstanding that 

 they were exposed to some additional danger, might sur- 

 vive, and from being favoured through sexual selection, 

 would procreate their kind. The brightly-coloured young 

 males being destroyed and the mature ones being suc- 

 cessful in their courtship, may account, on the principle 

 of a relation existing between the period of variation 

 and the form of transmission, for the males alone of 

 many birds, having acquired and transmitted brilliant 

 colours to their male offspring alone. But I by no 

 means wish to maintain that the influence of age on 

 the form of transmission is indirectly the sole cause of 

 the great difference in brilliancy between the sexes 

 of many birds. 



As with all birds in which the sexes differ in colour, it 

 is an interesting question whether the males alone have 

 been modified through sexual selection, the females 

 being left, as far as this agency is concerned, unchanged 

 or only partially changed ; or wdiether the females have 

 been specially modified through natural selection for the 

 sake of protection, I will discuss this question at con- 

 siderable length, even at greater length than its intrinsic 

 importance deserves ; for various curious collateral points 

 may thus be conveniently considered. 



VOL. II. M 



