Chap. XVI. THE YOUNG LIKE THE ADULT FEMALES. 191 



age as that possessed by the three first species during 

 the winter and in their immature state ; and this plum- 

 age, which is common to several distinct species at 

 different ages and seasons, probably shews us how the 

 progenitor of the genus was coloured. In all these 

 cases, the nuptial plumage which we may assume was 

 originally acquired by the adult males during the breed- 

 insf-season, and transmitted to the adults of both sexes 

 at the corresponding season, has been modified, whilst 

 the winter and immature plumages have been left un- 

 changed. 



The question naturally arises, how is it that in these 

 latter cases the winter plumage of both sexes, and in 

 the former cases the plumage of the adult females, as 

 well as the immature plumage of the young, have not 

 been at all affected ? The species which represent each 

 other in distinct countries will almost always have 

 been exposed to somewhat different conditions, but we 

 can hardly attribute the modification of the plumage 

 in the males alone to this action, seeing that the 

 females and the young, though similarly exposed, have 

 not been affected. Hardly any fact in nature shews 

 us more clearly how subordinate in importance is the 

 direct action of the conditions of life, in comparison 

 with the accumulation throuoh selection of indefinite 

 variations, than the surprising difference between the 

 sexes of many birds ; for both sexes must have con- 

 sumed the same food and have been exposed to the 

 same climate. Nevertheless we ar« not precluded from 

 believing that in the course of time new conditions 

 may produce some direct effect ; we see only that this 

 is subordinate in importance to the accumulated results 

 of selection. When, however, a species migrates into 

 a new country, and this must precede the formation of 

 representative species, the changed conditions to which 



