212 SEXUAL SELECTION: BIRDS. [Part II. 



could have been effected at the same time with the two 

 sexes of the same species. Mr. Salvin states, as we have 

 seen in the eighth chapter, that with certain humming- 

 birds the males greatly exceed in number the females, 

 while with other species inhabiting the same country the 

 females greatly exceed the males. If, then, we might as- 

 sume that during some former lengthened period the males 

 of the Juan Fernandez species had greatly exceeded the 

 females in number, but that during another lengthened 

 period the females had greatly exceeded the males, we 

 could understand how the males at pne time, and the 

 females at another time, might have been rendered beauti- 

 ful by the selection of the brighter-colored individuals of 

 either sex; both sexes transmitting their characters to 

 their young at a rather earlier age than usual. Whether 

 this is the true explanation I will not pretend to say ; but 

 the case is too remarkable to be passed over without 

 notice. 



We have now seen in numerous instances, under all 

 six classes, that an intimate relation exists between the 

 plumage of the young and that of the adults, either of one 

 sex or both sexes. These relations are fairly well ex- 

 plained on the principle that one ,sex — this being in the 

 great majority of cases the male — first acquired through 

 variation and sexual selection bright colors or other orna- 

 ments, and transmitted them in various wavs, in ac- 

 cordance with the recognized laws of inheritance. Why 

 variations have occurred at different periods of life, even 

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

 know; but with respect to the form of transmission, one 

 important determining cause seems to have been the age 

 at which the variations first appeared. 



From the principle of inheritance at corresponding 

 ages, and from any variations in color which occurred in the 



