her to be beautiful. Under these circumstances, however, it
is more necessary to her welfare that her consort be vigorous rather
than that he be handsome. Hence in the human species beauty has become
the prerogative of the woman, and this is increasingly the case the
higher the civilization. Whether woman suffrage and self-support will
reverse this process remains to be seen. There are indications that
point that way.

There are many biologists who are at present expressing serious doubt
as to the validity of sexual selection. As in the previous cases of
protective coloration, I believe it will be wise for us to retain,
even though with an interrogation point behind it, the idea of sexual
selection until such time as those who object to it have furnished us
with another theory which will more nearly account for the observed
facts. While entirely conscious of the possibility that there is a
weak spot in the theory, we will still tentatively hold to sexual
selection. The fact that beauty in women is so intensely attractive
to man, and that vigor and manliness in man are so attractive to
women, leads us to infer that among the lower animals, although of
course in a vastly less degree, vigor and beauty are also attractive.
The weakest point of the position lies in the fact that it probably
presupposes a higher degree of capacity for appreciation on the part
of lower animals than they possess. Those who deny the truth of the
theory laugh at the idea that a butterfly can see clearly enough and
care enough for what it sees to notice whether its mate has wings of
one type or of another. The size, number and position of the spots on
the wings of many butterflies are so nearly constant that they cannot
of themselves have been entirely determined by the choice of the
insect. Yet this may not preclude the possibility of the fact that,
while the spots were produced through some other agency, certain types
of them were selected by sexual preference.

If attractive coloration is effective anywhere in the animal world, it
will possibly be found among the insects, but it is especially likely
to be found among the birds. Very many field workers in these groups
feel quite sure of the value of attractiveness. When butterflies chase
each other up and down, circling and doubling, following each other
for long distances, it would certainly seem as if they were pleased
with each other's appearance. Some naturalists, especially those who
have