The Descent of Man

feathers of humming-birds differ, why should
not the four central feathers have varied in this
one species alone, so as to have acquired white
tips? The variations may have been gradual, or
somewhat abrupt as in the case recently given
of the humming-birds near Bogota, in which
certain individuals alone have the "central tailfeathers
tipped with beautiful green." In the
female of the Urosticte I noticed extremely minute
or rudimental white tips to the two outer
of the four central black tail- feathers; so that
here we have an indication of change of some
kind in the plumage of this species. If we grant
the possibility of the central tail- feathers of the
male varying in whiteness, there is nothing
strange in such variations having been sexually
selected. The white tips, together with the small
white ear-tufts, certainly add, as the Duke of
Argyll admits, to the beauty of the male; and
whiteness is apparently appreciated by other
birds, as may be inferred from such cases as the
snow-white male of the Bell-bird. The state-