CHAr. 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- 
ing-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 through 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 are 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 
