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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