16 AN OUTLINE OF THE THEORY. 
tion) was set forth by Kant in a work which he published 
anonymously in 1775. 
In its relations to animal life a development theory 
was first clearly set forth by Karl Ernst von Baer (died 
1876). In his “Entwickelungsgeschichte der Tiere” 
(1828), the author explains “Entwickelung” as a progress 
from simple to complex forms. He believes that in evo- 
lution there is a fundamental idea that “goes through all 
the forms of cosmic and animal development.’”’ A 
predecessor of von Baer had _ been the Frenchman, 
Lamarck. From von Baer, Herbert Spencer, about 1850, 
adopted the definition of evolution. 
The hypothesis entered a new phase through Charles 
Darwin’s epochmaking work: “The Origin of Species.” 
The keynote of Darwin’s theory is Natural Selection, by 
which term the development of all living forms is referred 
to the working of certain laws which in the reproduction 
of plants and animals preserved those individuals which 
were best fitted to survive the struggle for existence. The 
Darwinian theory may be summarized thus: 
The Darwinian Hypothesis. 
1. Every kind of animal and plant tends to increase 
in numbers in a geometrical progression. 
2. Every kind of animal and plant transmits a gen- 
eral likeness, with individual differences, to its offspring. 
3. Past time has been practically infinite. 
4. Every individual has to endure a very severe 
struggle for existence, owing to the tendency to geome- 
trical increase of all kinds of animals and plants, while 
the total animal and vegetable population (man and his 
agency excepted) remains almost stationary. 
5. Thus, every variation of a kind tending to save 
the life of the individual possessing it, or to enable it 
more surely to propagate its kind, will in the long run be 
