999 
SEXUAL SELECTION: BIRDS. 
PAB 1 
will not pretend to say ; but the case is too remar 
to be passed over without notice. 
We have now seen in numerous instances under 
,l^ le 
# 
six classes, that an intimate relation exists between 
plumage of the young and that of the adults, eith ef ^ 
one sex or both sexes. These relations are fairly "h 
explained on the principle that one sex — this being j 
the great majority of cases the male— Hist aeq 113 '^, 
through variation and sexual selection bright col° 1 ^ 
or other ornaments, and transmitted them in va r,a 
ways, in accordance with the recognised laws of ] ' n ' , 
ritance. \\ 1 ) y variations have occurred at differ; 
periods of life, even sometimes with the species of 
same group, we do not know; but with resp 6 ^.^ 
the form of transmission, one important detertfi u ‘, “ 
cause seems to have lu cn the age at which the 
tions first appeared. 
Ire 
ooiw 
m 
rom the principle of inheritance at correspo 
ages, and from any variations in colour which ocO'j 
in the males at an early age not being then selects 1 
the contrary being often eliminated as dangerous, " 3 
similar variations occurring at or near the P er3 '° 
reproduction have been preserved, it follows 
n \iS 
ti’ 1 ? 
plumage of the young will often have been left 
difie 3 , or but little modified. We thus get some if * 
into the colouring of the progenitors of our e* 3 * gl] j 
species. In a vast number of species iu five out o ^ 
six classes ol eases, the adults of one sex or hot 1 
brightly coloured, at least during the breeding- 8 ^! 
whilst the young are invariably less brightly ooh ,u 
than the adults, or are quite dull-coloured; for 
stance is known, as far as I can discover, of the ) 3 g j 
of dull-coloured species displaying bright colon 1 *' 
