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In order to show that any process of Organic Evolution, 
by which an advance in the complexity of organisation 
has been brought about, has been influenced by Natural 
Selection, one of two methods might be adopted. It might 
be proved that Natural Selection has been at work in all 
cases, or in some cases, to produce a transmutation of 
species ; and from thence it might be inferred that the 
principle, active in the transmutation of species, must have 
been active in the process of Organic Evolution at large. 
Or, on the other hand, it might be assumed that the 
successive stages of development which the theory pre 
supposes are represented by organisms existing at the 
present day ; or, at the least, that such organisms enable 
us to conjecture what the primordial forms actually were ; 
and then, by observation of, or experiment upon, existing 
forms, it might be possible for us to conjecture what took 
place from the very first stages of Organic Evolution up 
to the present time. Now, both of these arguments have 
been employed by Mr. Herbert Spencer in his Essay on 
The Factors of Organic Evolution, in which he endeavours 
incidentally to show that Natural Selection has played its 
part in bringing about the first steps of the evolution of 
organic life out of a primordial protoplasm. I say he 
incidentally shows this, because the main contention of 
the Essay is to prove that there are three factors of 
Organic Evolution, viz.: the inherited effect of use and 
disuse, Natural Selection, and the “direct action of en 
vironing matters and forces.” But if this Essay is read 
from the point of view from which we have now to con 
sider it, it may be regarded as an attempt to show how 
Natural Selection is manifested in the earliest stages of 
Organic Evolution. 
In the first place, let us take note of the method of 
argument by which Mr. Spencer endeavours to show that