probable that female birds prefer the more attractive males, no one who
admits the agency of sexual selection in any case will deny that a
simple dark spot with some fulvous shading might be converted, through
the approximation and modification of two adjoining spots, together
with some slight increase of colour, into one of the so-called elliptic
ornaments. These latter ornaments have been shewn to many persons, and
all have admitted that they are beautiful, some thinking them even more
so than the ball-and-socket ocelli. As the secondary plumes became
lengthened through sexual selection, and as the elliptic ornaments
increased in diameter, their colours apparently became less bright; and
then the ornamentation of the plumes had to be gained by an improvement
in the pattern and shading; and this process was carried on until the
wonderful ball-and-socket ocelli were finally developed. Thus we can
understand and in no other way as it seems to me the present condition
and origin of the ornaments on the wing-feathers of the Argus pheasant.
From the light afforded by the principle of gradation from what we know
of the laws of variation from the changes which have taken place in
many of our domesticated birds and, lastly, from the character (as we
shall hereafter see more clearly) of the immature plumage of young
birds we can sometimes indicate, with a certain amount of confidence,
the probable steps by which the males have acquired their brilliant
plumage and various ornaments; yet in many cases we are involved in
complete darkness. Mr. Gould several years ago pointed out to me a
humming-bird, the Urosticte benjamini, remarkable for the curious
differences between the sexes. The male, besides a splendid gorget, has
greenish-black tail-feathers, with the four CENTRAL ones tipped with
white; in the female, as with most of the allied species, the three
OUTER tail-feathers on each side are tipped with white, so that the
male has the four central, whilst the female has the six exterior
feathers ornamented with white tips. What makes the case more curious
is that, although the colouring of the tail differs remarkably in both
sexes of many kinds of humming-birds, Mr. Gould does not know a single
species, besides the Urosticte, in which the male has the four central
feathers tipped with white.
The Duke of Argyll, in commenting on this case (53. The Reign of Law,
1867, p. 247.), passes over sexual selection, and asks, What
explanation does the law of natural selection give of such specific
varieties as these? He answers none whatever ; and I quite agree with
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