ideas which, in the last quarter of the nineteenth century, grew out of
Darwin's theories, in the endeavour to penetrate more deeply into the
problem of the evolution of the organic world. Within the narrow limits to
which this paper is restricted, I cannot attempt to discuss any of these.

V. ARGUMENTS FOR THE REALITY OF THE PROCESSES OF SELECTION.

(a) SEXUAL SELECTION.

Sexual selection goes hand in hand with natural selection. From the very
first I have regarded sexual selection as affording an extremely important
and interesting corroboration of natural selection, but, singularly enough,
it is precisely against this theory that an adverse judgment has been
pronounced in so many quarters, and it is only quite recently, and probably
in proportion as the wealth of facts in proof of it penetrates into a wider
circle, that we seem to be approaching a more general recognition of this
side of the problem of adaptation. Thus Darwin's words in his preface to
the second edition (1874) of his book, "The Descent of Man and Sexual
Selection", are being justified: "My conviction as to the operation of
natural selection remains unshaken," and further, "If naturalists were to
become more familiar with the idea of sexual selection, it would, I think,
be accepted to a much greater extent, and already it is fully and
favourably accepted by many competent judges." Darwin was able to speak
thus because he was already acquainted with an immense mass of facts,
which, taken together, yield overwhelming evidence of the validity of the
principle of sexual selection.

NATURAL SELECTION chooses out for reproduction the individuals that are
best equipped for the struggle for existence, and it does so at every stage
of development; it thus improves the species in all its stages and forms.