Chap. XVI.] SUMMARY. . 227 



unaffected, and therefore like each other. With species 

 having a distinct summer and winter plumage, the males 

 of which either resemble or differ from the females during 

 both seasons or during the summer alone, the degrees and 

 kinds of resemblance between the young and the old are 

 exceedingly complex ; and this complexity apparently 

 depends on characters, first acquired by the males, being 

 transmitted in various ways and degrees, as limited by 

 age, sex, and season. 



As the young of so many species have been but little 

 modified in color and in other ornaments, we are enabled 

 to form some judgment with respect to the plumage of 

 their early progenitors ; and we may infer that the beauty 

 of our existing species, if we look to the whole class, has 

 been largely increased since that period of which the im- 

 mature plumage gives us an indirect record. Many birds, 

 especially those which live much on the ground, have un- 

 doubtedly been obscurely colored for the sake of protec- 

 tion. In some instances the upper exposed surface of the 

 plumage has been thus colored in both sexes, while the 

 lower surface in the males alone has been variously orna- 

 mented through sexual selection. Finally, from the facts 

 given in these four chapters, we may conclude that weap- 

 ons for battle, organs for producing sound, ornaments of 

 many kinds, bright and conspicuous colors, have gener- 

 ally been acquired by the males through variation and 

 sexual selection, and have been transmitted in various 

 ways according to the several laws of inheritance — the fe- 

 males and the young being left comparatively but little 

 modified. 59 



69 1 am greatly indebted to the kindness of Mr. Sclater for having 

 looked over these four chapters on birds, and the two following ones on 

 mammals. By this means I have been saved from making mistakes about 

 the names of the species, and from giving any facts which are actually 

 known to this distinguished naturalist to be erroneous. But of course 

 he is not at all answerable for the accuracy of the statements quoted by 

 me from various authorities. 



