41G THE DESCENT OF MAN. 



effect. Nevertheless, after hearing how carefully the male Argus 

 pheasant displays his elegant primary wing-feathers, and erects 

 his ocellated plumes in the right position for their full effect; or 

 again, how the male goldfinch alternately displays his gold-be- 

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

 not attend to each detail of beauty. We can judge, as already re- 

 marked, of choice being exerted, only from analogy; and the men- 

 tal powers of birds do not differ fundamentally from ours. From 

 these various considerations we may conclude that the pairing of 

 birds is not left to chance; but that those males, which 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 diflBculty in understanding how male birds have grad- 

 ually acquired their ornamental characters. All animals present 

 individual differences, and as man can modify his domesticated 

 birds by selecting the individuals which appear to him the most 

 beautiful, so the habitual or even occasional 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 especially of their Secondary Sexual 

 Characters. — Variability and inheritance are the foundations for 

 the work of selection. That domesticated birds have varied great- 

 ly, their variations being inherited, is certain. That birds in a 

 state of nature have been modified into distinct races is now 

 universally admitted.'^ Variations may be divided into two 

 classes; those which appear to our ignorance to arise spontane- 

 ously, and those which are directly related to the surrounding 

 conditions, so that all or nearly all the individuals of the same 

 species are similarly modified. Cases of the latter Mnd have 

 recently been observed with care by Mr. J. A. Allen," who shows 



*> According; to Dr. Blasius ('Ibis,' vol. ii. 1860, p. 297), tliere are 425 

 indubitable species of birds which breed in Europe, besides sixty forms, 

 which are frequently regarded as distinct species. Of the latter, 

 Blasius thinks that only ten are really doubtful, and that the other fifty 

 ought to be united with their nearest allies; but this shows that there 

 must be a considerable amount of variation with some of our Euro- 

 pean birds. It is also an unsettled point with naturalists, whether 

 several North American birds ought to be ranked as specifically dis- 

 tinct from the corresponding European species. So again many North 

 American forms which until lately were named as distinct species, 

 are now considered to be local races. 



** 'Mammals and Birds of East Florida,' also an 'Ornithological 

 Keconnoissance of Kansas,' &c. Notwithstanding the inlluenee of 

 climate on the colors of birds, it is difiicult to account for the dull 

 or dark tints of almost all the species inhabiting certain countries. 



