1026 The American Naturalist. (November, 
venience of those ornamental appendages during the period of 
reproduction? 
Added to these necessary results of sexual selection we should 
note the fact that, in proportion to the higher coloration or other 
masculine superiority of ornament over that of the female of the 
same species, all birds are more pugnacious and destructive to 
their rivals, and this tendency among those of polygamous habits. 
finds further vent in their destruction of the eggs and newly- 
hatched young. 
From what has been said we may reasonably assume that 
strongly-marked, sexually limited, secondary characters, and a 
combative, irritable disposition, being ever associated with the 
habit of polygamy, they therefore must be in some way interde- 
pendent, and the one naturally resultant from the other. Nor do 
the results of inquiry in this direction refute such assumption, 
however they may seem to fail to establish its verity or give a 
Satisfactory solution of the problematic causes of polygamy as 
practiced by birds. Shall we consider, then, that the polygamous 
habit is a cause of the tendency to perfection of secondary 
sexual characters, or that it is a dunes of that tendency? I in- 
cline to the latter opinion. 
As we descend in the scale of being the lower orders become 
more strictly monogamous, till finally, among the lowest, androgy- 
nous forms appear, multiplying ad infinitum among the least 
specialized; whereas, if we ascend from these it is noticeable how 
the disposition to polygamous unions is confined to the highest — 
type of a genus or the higher genera of the sub-order. 
The genesis of to-day is an epitome of the genesis of those p. 
myriad yesterdays we call the past. If this be true we have no E 
alternative but in the belief that birds originally practiced monog- d 
amy only, that ancestral forms presented no sexual disparity in 
size, coloration, or ornamentation, and that, in the case of the 
Gallinze, its representatives may have originated from an obscure- 
ly-tinted, plain-haunting, monogamous ancestor. 
Given, then, such a starting point, we advance on the suppo- 
sition that sexual selection by the female, according to the stand- 
* For full discussion on these points see “Descent of Man," Chaps. XV. and XVI. 
