CHAPTER III 
VARIATION 
The assumption of Darwin and Wallace that variations are 
haphazard in origin and indefinite in direction—If these 
assumptions be not correct Natural Selection ceases to be the 
fundamental factor in evolution—Darwin’s views regarding 
variation underwent modification—He eventually recognised 
the distinction between definite and indefinite variations, and 
between continuous and discontinuous variations—Darwin 
attached but little importance to either definite or discon- 
tinuous variations—Darwin’s views on the causes of variations 
—Criticism of Darwin’s views—Variations appear to occur 
along certain definite lines—There seems to be a limit to the 
extent to which fluctuating variations can be accumulated— 
De Vries’ experiments—Bateson on “discontinuous varia- 
tion ”—Views held by De Vries—Distinction between con- 
tinuous and discontinuous variations—The work of De Vries— 
Advantages enjoyed by the botanist in experimenting on the 
making of species—Difficulties encountered by the animal 
breeder— Mutations among animals—The distinction between 
germinal and somatic variations—The latter, though not 
transmitted to offspring, are often of considerable value to 
their possessor in the struggle for existence. 
S we have already seen, the Darwinian 
theory, unlike that of Lamarck, does 
not attempt to explain the origin of 
variations. It is content with the 
fact that variations do occur. 
Although Darwin did not try to explain how 
it is that variation occurs, and was very guarded 
52 
