^22 The Descent of Man. Pabt II. 



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 

 tlie female, are under ordinary circumstances accepted. If this 

 be admitted, there is not much difficulty in understanding how 

 male birds have gradually acquired their ornamental characters. 

 AU animals present individual diflferenoes, and as man cia 

 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 

 greatly, 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 spon- 

 taneously, 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 kind have 

 recently been observed with care by Mr. J. A. Allen,'* who shews 



'^ Accoi-ding toDr. Blasius ('Ibis,' difficult to account for the dull or 



vol. ii. 1860, p. 297), tliere are 425 darlt tints of almost all tlie species 



indubitable species of birds which inhabiting certain countries, for 



breed in Europe, besides sixty forms, instance, the Galapagos Islands under 



which are frequently regarded as the equator, the wide temperate 



distinct species. Of the latter, plains of Patagonia, and, as it ap- 



Blasius thinks that only ten are pears, Egypt (see Mr. Hartshorne 



really doubtful, and that the other in the 'American Naturalist,* 1873, 



fifty ought to be united with their p. 747). These countries are open, 



nearest allies ; but this shews that .ind afford little shelter to birds; 



there must be a considerable amount but it seems doubtful whether the 



of variation with some of our Euro- absence of brightly coloured species 



pean birds. It is also an uni;ettied can be explained on the principle o^ 



point with naturalists, whether protection, for on the Pampas, which 



several North American birds ought are equally open, though covered 



to be ranked as specifically distinct by green grass, and where the birds 



from the corresponding European would be equally exposed to danger, 



Rpecies. So again many North Ame- many brilliaut and conspicuously 



rican forms which until lately were coloured species are common. I 



iian:sd as distinct species, are now have sometimes speculated whether 



considered to be local races. the prevailing dull tints of tJe 



'* ' JIammals and Birds of East scenery in the above named conntrie: 



Florida,' also an ' Ornithological Re- may not have affected the apprecia- 



connaissauce of Kansas, &;c. Not- t'on of bright colours by tht birdi 



ft'itht^tanding the influence of cU- mliabiting them. 

 luRte on the i;olours of birds, it is 



