The Making of Species 
act of pairing seems to tell against the theory of 
sexual selection, or at any rate to indicate the 
purely mechanical nature of the performance. 
Finn has witnessed this post-nuptial display 
at the Zoological Gardens (London) in the 
pied wagtail, the peacock, the Andaman Teal 
(NMetiium albigulare), the Avocet, the Egyptian 
Goose (Chenatopex egyptiaca), and the Maned 
Goose (Chenonetta jubata). 
Another objection to the theory that the bright 
colours of cock birds are due to feminine selection 
is presented by those birds which breed in im- 
mature plumage. Darwin admits that this objec- 
tion would be a valid one “if the younger and 
less ornamental males were as successful in 
winning females and propagating their kind as 
the older and more beautiful males. But,” he 
continues, ““we have no reason to suppose that 
this is the case.” 
Unfortunately for the theory of sexual selection, 
there is evidence to show that the cock Paradise 
Fly-catcher (Zerpsiphone paradzsz) in immature 
plumage is quite as successful in obtaining a 
mate as is the cock in his final plumage. The 
cock of this beautiful species has a chestnut 
plumage in his second year, and a white one 
in the third and subsequent years of his life. 
Nevertheless, a considerable proportion of the 
nests found belong to chestnut cocks. 
Darwin was of opinion that any novelty in 
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