124 SEXUAL SELECTION : BIRDS. Part U. 



wing-featliers, and erects his ocellated plumes in the 

 right position for their full effect ; or again, how the 

 male goldfinch alternately displays his gold-bespangled 

 wings, we ought not to feel too sure that the female 

 does not attend to each detail of beauty. We can 

 judge, as already remarked, of choice being exerted, 

 only from the analogy of our own minds ; and the 

 mental powers of birds, if reason be excluded, do not 

 fundamentally differ from ours. From these various 

 considerations we may conclude that the pairing of 

 birds is not left to chance ; but that those males, ^^•hich 

 are best able by their various charms to please or excite 

 the female, are under ordinary circumstances accepted. 

 If this be admitted, there is not much difticulty in 

 understanding how male birds have gradually acquired 

 their ornamental characters, i^ll animals present indi- 

 vidual differences, and as man can modify his domesti- 

 cated birds by selecting the individuals which appear 

 to him the most beautiful, so the habitual or even occa- 

 sional preference by the female of the more attractive 

 males would almost certainly lead to their modification ; 

 and such modifications might in the course of time be 

 augmented to almost any extent, compatible with the 

 existence of the species. 



Variability of Birds, and es^ecialhj of their secondary 

 Sexual Characters. — Variability and inlieritance are the 

 foundations for the work of selection. That domesti- 

 cated birds have varied greatly, their variations being 

 inherited, is certain. That birds in a state of nature 

 present individual differences is admitted by every 

 one ; and that they have sometimes been modified into 

 distinct races, is generally admitted. ^^ Variations are 



31 According to Dr. Blasius ('Ibis,' vol. ii. 186D, p. 297), tlicre are 

 425 indubitable species of birds wliieh breed in Europe, besides 60 



