re fertile
with one another, that link will be wanting. For, so long, selective
breeding will not be proved to be competent to do all that is required
of it to produce natural species.

I have put this conclusion as strongly as possible before the reader,
because the last position in which I wish to find myself is that of
an advocate for Mr. Darwin's, or any other views--if by an advocate is
meant one whose business it is to smooth over real difficulties, and to
persuade where he cannot convince.

In justice to Mr. Darwin, however, it must be admitted that the
conditions of fertility and sterility are very ill understood, and that
every day's advance in knowledge leads us to regard the hiatus in his
evidence as of less and less importance, when set against the multitude
of facts which harmonize with, or receive an explanation from, his
doctrines.

I adopt Mr. Darwin's hypothesis, therefore, subject to the production of
proof that physiological species may be produced by selective breeding;
just as a physical philosopher may accept the undulatory theory of
light, subject to the proof of the existence of the hypothetical ether;
or as the chemist adopts the atomic theory, subject to the proof of the
existence of atoms; and for exactly the same reasons, namely, that it
has an immense amount of prima facie probability: that it is the only
means at present within reach of reducing the chaos of observed facts
to order; and lastly, that it is the most powerful instrument of
investigation which has been presented to naturalists since the
invention of the natural system of classification, and the commencement
of the systematic study of embryology.

But even leaving Mr. Darwin's views aside, the whole analogy of natural
operations furnishes so complete and crushing an argument against
the intervention of any but what are termed secondary causes, in the
production of all the phenomena of the universe; that, in view of the
intimate relations between Man and the rest of the living world, and
between the forces exerted by the latter and all other forces, I can see
no excuse for doubting that all are co-ordinated terms of Nature's great
progression, from the formless to the formed--from the inorganic to the
organic--from blind force to conscious intellect and will.

Science has fulfilled her function when she has ascertained and
enunciated truth; and were these pages addressed to men of science only,
I should now close this essay