192 
SEXUAL selection: birds. 
Pact i 
,0 
they will almost always have been exposed will c£,u 
them to undergo, judging from a widely-spread analog 
a certain amount of fluctuating variability. la 
0 
case sexual selection, which depends on an elei» eI : 
eminently liable to change — namely the taste or 
ration of the female— will liave had new shades of col l)l 
° d < 
sexual selection is always at work, it would (jndg^ 
from what we know of the results on domestic ani® 3 ^ 
of man’s unintentional selection), be a surprising f ft(jt f 
tiy 
or other differences to act on and accumulate ; a 11 *' , 
- 'W 
ills 
animals inhabiting separate districts, which can 
cross and thus blend their newly-acquired charac 
were not, after a sufficient lapse of time, differ 611 . ) 
modified. These remarks likewise apply to the n n P fl ‘ ir 
or summer plumage, whether confined to the tua! eS 
common to botli sexes. 
JJi* 
4 
‘vat 013 
Although the females of the above closely 
species, together with their young, differ hardly . 
from each other, so that the males alone can be di g 
guished, yet in most cases the females of the sp et>3 ^ 
within the same genus obviously differ from each ot |11 ^ 
The differences, however, are rarely as great as bet" ^ 
the males. We see this clearly in the whole fain''- 3 , 
the Gallinaceie : the females, for instance, of the c ° 
uupiu jjucaotiiiL, ami trsjjtjuijuxy ui tilt* 
Amherst pheasant — of the silver pheasant and the 
fowl — resemble each other very closely in colour 
id 
ylfi'f 
mon and J apan pheasant, and especially of the gold 00 , 
u_, . 
the males differ to an extraordinary degree. So ** 
with the females of most of the Cotingidm, FringH 113 ^ 
and many other families. There can indeed be no do* 
DC 1 
that, as a general rule, the females have been 
fled to a less extent than the males. Some fe' v 
IllO 
bP . 
,tio p ' 
however, offer a singular and inexplicable except 1 " 
thus the females of Paradisea, apoda and P. P a f l ‘\-e 
differ from each other more than do their resp eC 
