Introductory. 15 
operating immediately in numberless acts of special 
creation, and the theory of natural causes as a whole, 
whether these happen, or do not happen, to have been 
hitherto discovered. . 
This much by way of preliminaries being under- 
stood, we have next to notice that whichever of the 
two rival theories we choose to entertain, we are not 
here concerned with any question touching the origin 
of life. We are concerned only with the origin of 
particular forms of life—that is to say, with the origin 
of species. The theory of descent starts from life as 
a datum already granted. How life itself came to be, 
the theory of descent, as such, is not concerned to 
show. Therefore, in the present discussion, I will take 
the existence of life as a fact which does not fall 
within the range of our present discussion. No doubt 
the question as to the origin of life is in itself a deeply 
interesting question, and although in the opinion of 
most biologists it is a question which we may well 
hope will some day fall within the range of science to 
answer, at present, it must be confessed, science is not 
in a position to furnish so much as any suggestion upon 
the subject; and therefore our wisdom as men of 
science is frankly to acknowledge that such is the case. 
We are now in a position to observe that the theory 
of organic evolution is strongly recommended to our 
acceptance on merely antecedent grounds, by the fact 
that it is in full accordance with what is known as the 
principle of continuity. By the principle of continuity 
is meant the uniformity of nature, in virtue of which 
the many and varied processes going on in nature are 
due to the same kind of method, i.e. the method of 
