The Fruitful Facets of Galton's Polyhedron 447
other creature, bears so many distinct features ("a number far higher than
comparative and systematic science can by any means accumulate in its
descriptions"—1909a, volume 2, p. 665), geological time becomes positively
bounteous for requirements of the mutation theory. De Vries epitomized his view
in an "equation" (not really a mathematical formula, but a set of concepts
epitomized by letters): M x L = BT, or number of mutations times length of
intervals between mutations equals "biological time." So long as biological time
doesn't exceed available geological time, Kelvin's paradox may be resolved.
But de Vries' main contribution to macroevolution does not lie in this explicit
geological aid (soon made irrelevant by radioactive extension of the earth's age in
any case). Rather, de Vries formulated a fully articulated macroevolutionary theory
based on the application of Darwinian logic to the higher level of species and
trends—a true theory of "species selection" (even so named by de Vries!). I do not
think that de Vries ever recognized the full import of what he had done—for he
never grants the theme real prominence, and pieces of the argument lie scattered
throughout his writing. But de Vries developed all the parts, and they do cohere.
His acute understanding of Darwinian logic (a grasp that also led him to reject
selection where he felt that such a mechanism couldn't apply) drove him on and
informed all the disparate elements of his thinking.
De Vries developed his macroevolutionary concepts as a set of logical
implications from the Mutation Theory. He recognized, first of all, that an origin of
new species by recurrent and effectively identical saltation provides no variation
for the working of any Darwinian process of selection: " [Perhaps] the mutants of
one type ... would not be pure ... but would exhibit different degrees of deviation
from the parent. The best would then have to be chosen in order to get the new
type in its pure condition. Nothing of the kind, however, was observed. All the
oblonga mutants were pure oblongas. The pedigree shows hundreds of them in the
succeeding years, but no difference was seen and no material for selection was
afforded" (1905, pp. 559-560).
All effective evolutionary variation exists only among the "elementary
species" formed by mutation from a parental stock, not among individual
organisms within these species. In principle, therefore, if selection works as an
evolutionary force at all, Darwin's process can only sort elementary species, not
organisms within populations. De Vries clearly recognizes the difference between
the conventional Darwinian form of organismal selection and his proposal for
selection among elementary species: "The struggle for existence, that is to say the
competition for the means of subsistence, may refer to two entirely different
things. On the one hand, the struggle takes place between the individuals of one
and the same elementary species, on the other between the various species
themselves. The former is a struggle between fluctuations, the latter between
mutations" (1909a, volume 1, pp. 211-212).
Horticulturists, de Vries noted, recognize the two modes with different names
(1905, pp. 604-605)—"race-breeding" for the limited and relatively ineffective
Darwinian sorting based on fluctuating variation among organisms