VARIATION 517 
attempt to explain it, his arguments for evolution were much 
more convincing than those of his predecessors, and his explana- 
tion was so well based upon facts and so well organized that it 
was widely accepted. His book, the Origin of Species, published 
in 1859, in which he set forth his argument for evolution and its 
explanation, was based 
upon 20 years of careful 
observat.on, experiments, 
and thought, and is one 
of the greatest books ever 
published. To this book 
is largely due the accept- 
ance of the doctrine of 
evolution as based upon 
natural selection, and 
modern biology is said to ~ 
date from this book. The 
two fundamental concep- 
tions of this book are: 
(1) that the process of 
creation is evolution; and 
(2) that the process of 
evolution is based upon 
natural selection. Fic. 464.— Charles Darwin, the noted 
scientist, to whose work the establishment 
of the theory of evolution by natural selec- 
tion is chiefly due. 
Natural Selection. — 
According to Darwin’s 
theory of matural selec- 
tion, the individuals of the plant and animal world are in- 
volved in continuous competition in nature, and only those 
best adapted to their surroundings survive. Thus through 
the destruction of those individuals not able to survive in the 
struggle for existence, a selective process, which permits only 
certain individuals out of a large number to live and propa- 
gate, is thereby established. Darwin’s theory of natural selec- 
tion involves five fundamental conceptions, — variation, inheri- 
tance, fitness for environment, struggle for existence, and survival 
of the fittest. 
Variation. — Variation is the fundamental fact in Darwin’s 
theory of natural selection. By variations is meant the devia- 
tions of organisms from a type chosen as a standard of compari- 
