455 
to the set of natural causes which formed the motive power and 
guiding principle by which the change from one species to another 
was brought about.”—(Nineteenth Century, vol. vii., ftp. Q3-4.) 
Moreover, the assertion that there is only one physical 
method of bringing about the phenomenon of Organic 
Evolution, assumes that all other theories of the sub 
ject have been proved to be false. If such a definition 
is made the starting point, it is obvious that all discussion 
is impossible. But however that may be, it is obvious that 
the believer in Mixed Darwinism should be careful in his 
use of terms; making a distinction between the idea of 
Organic Evolution in the abstract and Organic Evolution 
regarded as the result of different methods, of selective 
agency alone, of transforming agency alone, or of a 
combination of both. 
The process of Organic Evolution, considered in the 
abstract and apart from the laws by which it is brought 
about, may be defined as a theory of descent with modi 
fication. In other words, it asserts the principle of heredity 
by virtue of which like produces like—the principle of 
variation by virtue of which modifications of structure 
take place ; and it implies that these variations may also 
be inherited. Pure Darwinism defines Organic Evolution 
as a theory of descent, with modification, by means of 
Natural Selection. Specific likeness is accompanied with 
individual differences, and the favourable variations among 
them survive through the action of Natural Selection. The 
theory of transformation asserts that Organic Evolution 
is brought about by descent with modification—the modi 
fications being due to the laws of variation generally, and 
especially to the law whereby an organism is adapted by 
the circumstances to the circumstances ; and these modifi 
cations are inherited, apart from the principle of selection. 
Mixed Darwinism asserts that there is in nature a selection