428 THE STRUCTURE OF EVOLUTIONARY THEORY
origin of species. Taking the traditional anti-Darwinian line, and employing a
striking metaphor, de Vries claims that selection cannot construct anything new,
but can only operate as a sieve to preserve favorable forms produced by some other
process: "Natural selection is a sieve. It creates nothing, as is so often assumed; it
only sifts. It retains only what variability puts into the sieve. Whence the material
comes that is put into it should be kept separate from the theory of its selection.
How the struggle for existence sifts is one question; how that which is sifted arose
is another" (1909a, volume 2, p. 609).
- If new species originate in single leaps, then their origin must be non-
adaptive, however much their future survival may require a fortuitous match with
local environments: "It explains in a very simple way the existence of the vast
number of specific characters which are quite useless or as to the use of which we
have no idea at all... According to the commonly accepted theory of selection only
characters advantageous to their possessors should arise; according
5 - 9A. Oenothera Lamarckiana contrasted with two of De Vries' mutations. From Volume 2 of
De Vries' Mutation Theory.