Chap. XVI.] THE YOUNG LIKE THE ADULT FEMALES. 183 



how the progenitor of the genus was colored. 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, while the 

 winter and immature plumages have been left unchanged. 

 The question naturally arises. How is it that in these 

 latter cases the winter plumage of both sexes, and ia 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 dis- 

 tinct countries will almost always have been exposed to 

 somewhat different conditions, but we can hardly attrib- 

 ute 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 shows 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 be- 

 tween the sexes of many birds ; for both sexes must have 

 consumed 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 sub- 

 ordinate in importance to the accumulated results of se- 

 lection. When, however, a species migrates into a new 

 country, and this must precede the formation of represent- 

 ative species, the changed conditions to which they will 

 almost always have been exposed will cause them to 

 undergo, judging from a widely-spread analogy, a certain 

 amount of flixctuating variability. In this case sexual 

 selection, which depends on an element eminently liable 

 to change — namely, the taste or admiration of the female 

 — will have had new shades of color or other differences 



