156 THE COURTSHIP OF ANIMALS 



or later seek a mate elsewhere, deserting the phlegmatic 

 bird as if under the impression that she had made the 

 mistake of settling down with one of her own sex. There 

 is no need that the female should have to " select " the 

 best performer of a number of males displaying at the 

 same time and place as a number of rivals. " 



Finally, the ornamental crests and frills, and the vivid 

 hues which so many birds display have not arisen, as 

 is generally supposed, as a direct result of the selection, 

 by the females, of themost vividly coloured, or ornamented, 

 from among a number of suitors presenting varying degrees 

 of intensity in ornamentation. Such "frills and fur- 

 belows " are to be regarded as " expression points " of 

 internal variations in the germ-plasm, which have been 

 free to develop along their own lines because they have 

 not proved in disharmony with the conditions of the birds' 

 environment. Their development is to be traced to the 

 stimulating action of the " hormones " which control both 

 pigmentation and structure, as is shown by the fact that 

 both are modified by any interference with the glands 

 in question. Such ornamental features then are the 

 concomitants not the results of Sexual selection. 



The development of ornament, whether of colour oi 

 structure, may be taken then as an index of specialization, 

 and as one of the many manifestations of that variation 

 which is going on in every part of every living organism. 



So long as the continued increments in the development 

 of these characters do not hamper their possessors in 

 the struggle for existence, they are free to go on develop- 

 ing. Sexual selection, other things being equal, operates 

 by according the greatest number of descendants to the 

 most amorous, and not necessarily to those of the 

 brightest hues. 



