all cases necessary to reproduction--that this heightened male
attractiveness is a progressive force in the service of the race? If
so, examples will surely point in the direction of finding that among
those species where the sexual characters of the male, whether of
strength or of beauty, are most different from the female, sexual love
will find its most perfect expression; and further, that the males in
such case will be the most highly developed--the best parents and the
most social in their habits. The whole question, I think it must be
evident, turns upon this being proved.

But in the face of the facts before us this is just what we do not
find. Among birds (who in erotic development far excel all other
animals, not, indeed, excepting the human species, and thus must be
accepted as affording the most perfect examples of sexual development)
we have seen that the cases are not few in which the female equals, or
even exceeds the male in size and in strength. This is so with the
curlew, the merlin, the dunlin, the black-tailed goodwit, which is
considerably larger than the male, and the osprey, where the female is
also more spotted on the breast: these examples must be added to those
I have already given (page 58).

If we turn now to the beauty-test of brilliancy of plumage, we may
observe an even larger number of examples of almost identical likeness
between the sexes. Among British birds alone there are no fewer than
382 species, or sub-species,[83] in which the female closely resembles
the male. In some few of these examples, it is true, the colours of
the female are slightly duller, and in others the female is rather
smaller than the male, but the difference in each case is very slight.
It is specially significant to note that this similarity of plumage
occurs in some of the most beautiful of our birds, as, for instance,
the kingfisher and the jay, where the brilliant dresses of the sexes
are practically alike; the female robin shares the beauty of the male;
in all the families of the charming tits the sexes are alike; this is
also the case with the roller-bird with its gaily-coloured plumage;
and there is no difference between the white elegance of the female
and the male swan.

In the presence of such examples it seems to me impossible to refrain
from thinking that there is a mistake somewhere, and that less
importance is to be attached to the secondary sexual characters of the
male than is generally imagin