future I shall not pay attention to
unsupported expressions of opinion from any quarter: I shall consider
only such as are accompanied with some statement of the grounds upon
which the opinion is held. And, even as thus limited, I do not think it
will be found that the following exposition devotes any disproportional
amount of attention to the contemporary movements of Darwinian thought,
seeing, as we shall see, how active scientific speculation has been in
the field of Darwinism since the death of Mr. Darwin.

* * * * *

Leaving, then, these post-Darwinian questions to be dealt with
subsequently, I shall now begin a systematic _resume_ of the evidences
in favour of the Darwinian theory, as this was left to the world by
Darwin himself.

There is a great distinction to be drawn between the fact of evolution
and the manner of it, or between the evidence of evolution as having
taken place somehow, and the evidence of the causes which have been
concerned in the process. This most important distinction is frequently
disregarded by popular writers on Darwinism; and, therefore, in order to
mark it as strongly as possible, I will effect a complete separation
between the evidence which we have of evolution as a fact, and the
evidence which we have as to its method. In other words, not until I
shall have fully considered the evidence of organic evolution as a
process which somehow or another _has_ taken place, will I proceed to
consider _how_ it has taken place, or the causes which Darwin and others
have suggested as having probably been concerned in this process.

Confining, then, our attention in the first instance to a proof of
evolution considered as a fact, without any reference at all to its
method, let us begin by considering the antecedent standing of the
matter.

* * * * *

First of all we must clearly recognise that there are only two
hypotheses in the field whereby it is possible so much as to suggest an
explanation of the origin of species. Either all the species of plants
and animals must have been supernaturally created, or else they must
have been naturally evolved. There is no third hypothesis possible; for
no one can rationally suggest that species have been eternal.

Next, be it observed, that the theory of a continuous transmutation of
species is not logically bound to furnish a full explanation of _all_
the natural causes which it may suppo