556 THE DESCENT OF MAN'. 



We have now seen in all six classes that an intimate rela- 

 tion exists between the plumage of the young and the 

 adults, either- of one sex or both. These relations are 

 fairly well explained on the principle that one sex thie 

 being in the great majority of cases the male first acquired 

 through variation and sexual selection bright colors or 

 other ornaments and transmitted them in various ways in 

 accordance with the recognized laws of inheritance. Why 

 variations have occurred at different periods of life, even 

 sometimes with species of the same group, we do not know, 

 but with respect to the form of transmission one important 

 determining cause seems to be the age at which the varia- 

 tions first appear. 



From the principle of inheritance at corresponding ages 

 and from any variations in color which occurred in the 

 males at an early age not being then selected on the con- 

 trary being often eliminated as dangerous w-hile similar 

 variations occurring at or near the period of reproduction 

 have been preserved, it follows that the plumage of the 

 young will often have been left unmodified, or but little 

 modified. We thus get some insight into the coloring of 

 the progenitors of our existing species. In a vast number 

 of species in five out of our six classes of cases the adults of 

 one sex or of both are bright colored, at least during the 

 breeding-season, while the young are invariably less brightly 

 colored than the adults, or are quite dull colored; for no 

 instance is known, as far as I can discover, of the young of 

 dull-colored species displaying bright colors, or of the young 

 of bright-colored species* being more brilliant than their 

 parents. In the fourth class, however, in which the young 

 and the old resemble each other, there are many species 

 (though by no means all), of which the young are bright 

 colored, and, as these form old groups, we may infer that 

 their early progenitors were likewise bright. With this 

 exception, if we look to the birds of the world, it appears 

 that their beauty has been much increased since that 

 period, of which their immature plumage gives us a partial 

 record. 



On the Color of the Plum age in Relation to Protection. 

 It will have been seen that I cannot follow Mr. Wallace in 

 the belief that dull colors, when confined to the females, 

 have been in most cases specially gained for the sake of 



