450 THE STRUCTURE OF EVOLUTIONARY THEORY
the final combination of the two contending ideas. Reducing the
changeability of the species to distinct and probably short periods, it at once
explains how the stability of species perfectly agrees with the principle of
descent through modification (1905, p. 694).
In his earlier writings (1905, 1909a), de Vries strongly supported adaptation
as the primary result of trends forged by species selection. But he altered this
conviction in later articles, and thereby came to espouse the full range of internalist
critiques against Darwin (in questioning both gradualism and functionalism). In
1922, de Vries contributed a short, but highly revealing chapter to J. C. Willis'
famous critique of adaptation based on the correlation of geographic distribution
and geological longevity: Age and Area (Willis, 1922).
Of course, de Vries had always opposed adaptationism for the origin of
species (1922, p. 224) because selection cannot craft good design if species arise in
single steps: "Specific characters have evolved without any relation to their
possible significance in the struggle for life. The facts are contrary to the main
principle of the selection theory of Darwin" (1922, p. 226). De Vries interpreted
Willis' argument as a final proof for this linchpin of his theory—and he expressed
delight: "The general belief in adaptation as one of the chief causes of the
evolution of specific characters is best directly contradicted by the statistical
studies of Willis... This result must be considered as the one great proof, which
the mutation theory still wanted for its acceptance in the field of systematic
zoology and botany" (1922, p. 227).
But differentia of higher taxa arises by cumulation during species selection,
and may therefore be adaptive. "It is a curious fact that most of the striking
instances of beautiful adaptation to special forms of life are characters of genera
and sub-genera, or even of whole families, but not of single species. Climbing
plants and tendrils, insectivorous plants, desert types—submerged water plants,
and numerous other instances could be adduced" (1922, p. 22). (De Vries regarded
the distinction between nonadaptation in most defining traits of species, and
adaptation for the differentia of higher taxa, as virtual proof for the nonselectionist
origin of species by saltation and the functional origin of higher taxa by species
selection.)
Still later, however, and further inspired by Willis, de Vries reasserted even
this restricted role for adaptation—as he recognized that an a posteriori functional
correlation of form and environment (especially for broad characters of higher
taxa) need not indicate adaptive fashioning under current circumstances. Using an
argument of exaptation (Gould and Vrba, 1982, and Chapter 11), de Vries
recognized and embraced the alternative view that such characters arise for an
immediate reason (often nonadaptive), then radiate out randomly by Willis'
argument, and finally survive in environments that, by good fortune for the species,
favor a set of characters originally evolved for reasons unrelated to current
function:
Everywhere in nature, in geological periods as well as at present, the
morphological characters of newly originated types have no special
significance