276 
DARWINISM 
CHAP. 
than half of the known species. It is this class, therefore, that 
will afford us the best materials for a discussion of the problem, 
and that may perhaps lead us to a satisfactory explanation of 
the causes to which sexual colour is due. 
The most fundamental characteristic of birds, from our 
present point of view, is a greater intensity of colour in the 
male. This is the case in hawks and falcons; in many 
thrushes, warblers, and finches ; in pigeons, partridges, rails, 
plovers, and many others. When the plumage is highly 
protective or of dull uniform tints, as in many of the 
thrushes and warblers, the sexes are almost or quite identical 
in colour; but when any rich markings or bright tints are 
acquired, they are almost always wanting or much fainter in 
the female, as we see in the black-cap among warblers, and 
the chaffinch among finches. 
It is in tropical regions, where from a variety of causes 
colour has been developed to its fullest extent, that we find 
the most remarkable examples of sexual divergence of colour. 
The most gorgeously coloured birds known are the birds 
of paradise, the chatterers, the tanagers, the humming-birds, 
and the pheasant-tribe, including the peacocks. In all these 
the females are much less brilliant, and, in the great majority 
of cases, exceptionally plain and didl coloured birds. Not 
only are the remarkable plumes, crests, and gorgets of the 
birds of paradise entirely wanting in the females, but these 
latter are usually without any bright colour at all, and rank no 
higher than our thrushes in ornamental plumage. Of the 
humming-birds the same may be said, except that the females 
are often green, and sometimes slightly metallic, but from 
their small size and uniform tints are never conspicuous. 
The glorious blues and purples, the pure whites and intense 
crimsons of the male chatterers are represented in the females 
by olive-greens or dull browns, as are the infinitely varied 
tints of the male tanagers. And in pheasants, the splendour 
of plumage which characterises the males is entirely absent 
in the females, which, though often ornamental, have always 
comparatively sober and protective tints. The same thing 
occurs with many other groups. In the Eastern tropics 
are many brilliant birds belonging to the families of the 
warblers, flycatchers, shrikes, etc., but the female is always 
