30 THE HISTORY OF CREATION. 
properties have not as yet been observed by the experience 
of the senses. But Darwin’s theory does not assume such 
unknown conditions; it is based upon general properties 
of organisms that have long been recognized, and—as has 
been remarked—it is the exceedingly ingenious and com- 
prehensive combination of a number of phenomena which 
had hitherto stood isolated, which gives the theory its 
extraordinarily great and intrinsic value. By it we are 
for the first time in a position to demonstrate an active 
cause for all the known morphological phenomena in the 
animal and vegetable kingdoms; and, in fact, this cause is 
always one and the same, viz. the alternate action of Adap- 
tation and Inheritance, therefore a physiological, that is, a 
physico-chemical or mechanical, relationship. For these 
reasons the acceptance of the Doctrine of Filiation, as 
mechanically established by Darwin, is a binding and un- 
avoidable necessity’ for the whole domain of zoology and 
botany. 
As, therefore, in my opinion the immense importance of 
Darwin’s theory lies in the fact that it has mechanically 
explained those organic phenomena of forms which had 
hitherto been unexplained, it is perhaps necessary that I 
should here say a few words about the different ideas con- 
nected with the word “ explanation.” It is very frequently 
said, in opposition to Darwin’s theory, that it does indeed 
explain those phenomena by Inheritance and Adaptation, 
but that it does not at the same time explain those pro-_ 
perties of organic matter, and that therefore we do not 
arrive at first causes. This objection is quite correct, but it 
applies equally to all explanations of phenomena. We no- 
where arrive at a knowledge of first causes. The origin of 
