I believed that this process
might be simply explained as due to the cessation of the conservative
effect of natural selection. I said to myself that, from the moment in
which a part ceases to be of use, natural selection withdraws its
hand from it, and then it must inevitably fall from the height of its
adaptiveness, because inferior variants would have as good a chance of
persisting as better ones, since all grades of fitness of the part in
question would be mingled with one another indiscriminately. This is
undoubtedly true, as Romanes pointed out ten years before I did, and
this mingling of the bad with the good probably does bring about a
deterioration of the part concerned. But it cannot account for the
steady diminution, which always occurs when a part is in process of
becoming rudimentary, and which goes on until it ultimately disappears
altogether. The process of dwindling cannot therefore be explained as
due to panmixia alone; we can only find a sufficient explanation in
germinal selection.

IV. DERIVATIVES OF THE THEORY OF SELECTION.

The impetus in all directions given by Darwin through his theory of
selection has been an immeasurable one, and its influence is still felt.
It falls within the province of the historian of science to enumerate
all the 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