32 THE HISTORY OF CREATION. 
posteriori cannot rightly be placed in opposition, as is 
usually done. On the contrary, sensuous experience is 
the original source of all knowledge. For this reason alone, 
all our knowledge is limited, and we can never apprehend 
the first causes of any phenomena. The force of crystal- 
lization, the force of gravitation, and chemical affinity 
remain in themselves just as incomprehensible as do 
Adaptation and Inheritance. 
Seeing that Darwin’s theory explains from a single point 
of view the totality of all those phenomena of which we 
have given a brief survey, that it demonstrates one and 
the same quality of the organism as the active cause in all 
cases, we must allow that it gives us for the present all 
that we can desire. Moreover, we have good reason to hope 
that at some future time we shall learn to explain the first 
causes at which Darwin has arrived, namely, the properties 
of Adaptation and Inheritance ; and that we shall succeed in 
discovering in the composition of albuminous matter certain 
molecular relations as the remoter, simpler causes of these 
phenomena. There is indeed no prospect of this in the 
immediate future, and we content ourselves for the present 
with the tracing back of organic phenomena to two 
mysterious properties, just as in the case of Newton’s 
theory we are satisfied with tracing the planetary motions 
to the force of gravitation, which itself is likewise a mys- 
tery to us and not cognizable in itself. 
Before commencing our principal task, which is the care- 
ful discussion of the Doctrine of Descent, and the conse- 
quences that arise out of it, let us take an historical retro- 
spect of the most important and most widely spread of those 
views, which before Darwin men had elaborated concerning 
