262 THE HISTORY OF CREATION. 
organic self-preservation of which Schiller, the idealist (not 
Goethe, the realist !) says: 
** Meanwhile, until philosophy 
Sustains the structure of the world, 
Her workings will be carried on 
By hunger and by love.” * 
It is these two powerful fundamental instincts which, by 
their varying activity, produce such extraordinary differ- 
ences in species through the struggle for life. They are 
the foundations of the phenomena of Inheritance and 
Adaptation. We have, in fact, traced all phenomena of 
Inheritance to propagation, all phenomena of Adaptation to 
nutrition, as the two wider classes of material phenomena 
to which they belong. 
The struggle for life in natural selection acts with as 
much selective power as does the will of man in artificial 
selection. The latter, however, acts according to a plan and 
consciously, the former without a plan and unconsciously. 
This important difference between artificial and natural 
selection deserves especial consideration. For we learn by 
it to understand how arrangements serving a purpose 
can be produced by mechanical causes acting without an 
object, as well as by causes acting for an object. The 
products of natural selection are arranged even more for a 
purpose than the artificial products of man, and yet they 
owe their existence not to a creative power acting for a 
definite purpose, but to a mechanical relation acting uncon- 
* “ Hinstweilen bis den Bau der Welt 
Philosophie zusammenhilt, 
Erhalt sich ihr Getriebe 
Durch Hunger und durch Liebe. 
