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.S.)) 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