232 
SEXUAL SELECTION: BIRDS. 
PAB' r 1 
covered with snow. On the other hand we have rea® 0 ** 
to believe that whiteness has been gained by many bM s 
as a sexual ornament. We may therefore conclude th 1 ^ 
an early progenitor of the Ardea asha and the 
acquired a white plumage for nuptial purposes, i1,u 
transmitted this colour to t heir young; so that d 11 
young and the old became white "like certain exist' 11 " 
egiets , the whiteness having afterwards been retai* lt>l 
by the young whilst exchanged by the adults for 
strongly pronounced tints. But if we could look s u) 
further backwards in time to the still earlier progenitor 
of these two species, we should probably see the ad« lts 
dark-coloured. I infer that this would be the case, 
the analogy of many other birds, which are dark wk i,st 
young, and when adult are white ; and more especial 1 ’ 
from the case of the Ardea gularis, the colours of wlik* 1 
are the reverse of those of A. asha, for the young f 6 
dark-coloured and the adults white, the young having 
retained a former state of plumage. It appears there* 
fore that the progenitors in their adult condition of 
Ardea asha, the Biiphus, and of some allies, have n ncb ?r ' 
gone, during a long line of descent, the following ckang eS 
of colour ; firstly a dark shade, secondly pure wbk 6 ’ 
and thirdly, owing to another change of fashion (# 
may so express myself), their present slatv, reddish, ° r 
golden-buff tints. These successive changes are 
telligible only on the principle of novelty having h eelJ 
admired by birds for the sake of novelty. 
. Summary of the Four Chapters on Birds.— Mo st « lilIe 
birds are highly pugnacious during the breeding-sea® 0 * 1 ’ 
and some possess weapons especially adapted for fig 11 *' 
ing with their rivals. But the most pugnacious and th* 
best-armed males rarely or never depend for succ eSS 
solely on their power to drive away or kill their riv» ls > 
