Lntroductory. 3 
as to its method. In other words, not until I shall 
have fully considered the evidence of organic evolu- 
tion 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 a/7 the natural causes 
which it may suppose to have been at work. The 
radical distinction between the two theories consists 
in the one assuming an immediate action of some 
supernatural or inscrutable cause, while the other 
assumes the immediate action of natural—and there- 
fore of possibly discoverable—causes. But in order 
to sustain this latter assumption, the theory of descent 
is under no logical necessity to furnish a full proof of 
all the natural causes which may have been concerned 
in working out the observed results. We do not 
