200 
SEXUAL SELECTION: BIRDS. 
Part' 
tions in brightness which occurred in the females or "j 
the young would have been of no service to them, a® 
would not have been selected ; moreover, if danger 0 ' 1 ’ 
would have been eliminated. Thus the females and ^ 
young will either have been left unmodified, or, il11 
this has much more commonly occurred, will have 

partially modified by receiving through transference 
the males some of the successive variations. Both 
have perhaps been directly acted on by the eondit' fl|P 
..... . J - ■ 
tiH 
all 
r uu uy tut? 
of life to which they have long been exposed; but t® 
females from not being otherwise much modified , 
best exhibit any such effects. These changes and flJ 
- • &r 
.W 
others will have been kept uniform by the free in , 
crossing of many individuals. In some cases, esped"' ' 
w ith ground birds, the females and the young may P° S 
sibly have been modified, independents of the va^ e "' 
for the sake of protection, so as to have acquired 
•no * 11 
same dull-coloured plumage. 
Class II. When the adult female is more conspi^'f ^ 
than the adult male, the young of hotli sexes in their 
plumage resemble the adult male. — This class is eX& ct ' 
the reverse of the last, for the females are here _ 
brightly coloured or more conspicuous than the va^- ’ 
and the young, as far as they are known, reset® 
the adult males instead of the adult females. But t ^ 
difference between the sexes is never nearly so 
as occurs with many birds in the first class, and t ^ 
cases are comparatively rare. Mr. Wallace who f j';“ 
called attention to the singular relation which eS>S y 
between the less bright colours of the males and tl 1 ® 
performing the duties of incubation, lays great stress 
this point , 13 as a crucial test that obscure colours l" lVt 
13 ‘Westminster Review,’ July, 1867, and A. Murray, ‘ J ° urDa 
Travel,’ 1868, p. 83. 
