Two Types of Variation 71 
In his criticism of miscellaneous objections brought forward 
against the theory of natural selection after the publication of the 
first edition of The Origin of Species, Darwin stated his view on 
this point very clearly:—“The doctrine of natural selection or the 
survival of the fittest, which implies that when variations or individual 
differences of a beneficial nature happen to arise, these will be 
preserved’.” In this sentence the words “happen to arise” appear 
to me of prominent significance. They are evidently due to the 
same general conception which prevailed in Darwin’s Pangenesis 
hypothesis”. 
A distinction is indicated between ordinary fluctuations which are 
always present, and such variations as “happen to arise” from time 
to time®. The latter afford the material for natural selection to act 
upon on the broad lines of organic development, but the first do 
not. Fortuitous variations are the species-producing kind, which the 
theory requires; continuous fluctuations constitute, in this respect, 
a useless type. 
Of late, the study of variability has returned to the recognition 
of this distinction. Darwin’s variations, which from time to time 
happen to arise, are mutations, the opposite type being commonly 
designed fluctuations. A large mass of facts, collected during the 
last few decades, has confirmed this view, which in Darwin’s 
time could only be expressed with much reserve, and everyone 
1 Origin of Species (6th edit.), p. 169, 1882. 
2 Cf. de Vries, Intracellulare Pangenesis, p. 73, Jena, 1889, and Die Mutationstheorie, 
1. p. 68. Leipzig, 1901. 
3 [I think it right to point out that the interpretation of this passage from the Origin 
by Professor de Vries is not accepted as correct either by Mr Francis Darwin or by myself. 
We do not believe that Darwin intended to draw any distinction between two types of 
variation; the words ‘‘when variations or individual differences of a beneficial nature 
happen to arise” are not in our opinion meant to imply a distinction between ordinary 
fluctuations and variations which “happen to arise,” but we believe that “or” is here 
used in the sense of alias. With the permission of Professor de Vries, the following 
extract is quoted from a letter in which he replied to the objection raised to his reading 
of the passage in question: 
‘As to your remarks on the passage on page 6, I agree that it is now impossible to 
see clearly how far Darwin went in his distinction of the different kinds of variability. 
Distinctions were only dimly guessed at by him. But in our endeavour to arrive at a true 
conception of his view I think that the chapter on Pangenesis should be our leading guide, 
and that we should try to interpret the more difficult passages by that chapter. A careful 
and often repeated study of the Pangenesis hypothesis has convinced me that Darwin, 
when he wrote that chapter, was well aware that ordinary variability has nothing to do 
with evolution, but that other kinds of variation were necessary. In some chapters he 
comes nearer to a clear distinction than in others. To my mind the expression ‘happen to 
arise’ is the sharpest indication of his inclining in this direction. I am quite convinced 
that numerous expressions in his book become much clearer when looked at in this way.” 
The statement in this passage that ‘Darwin was well aware that ordinary variability 
has nothing to do with evolution, but that other kinds of variation were necessary ” is 
contradicted by many passages in the Origin. A. C. 8.] 
