different segments of a common pathway, but all supposedly living in an identical
environment—where others had reconstructed typical Darwinian monophyletic
trees of phylogeny from the same stratigraphic section of freshwater planorbids.
Hyatt, who engaged in a long and ultimately frustrating correspondence with
Darwin on this subject, believed that lineages followed a preordained "ontogeny"
of phyletic youth, maturity and old age, thus attributing the different internal
responses of lineages living in the same environment to their residence in different
stages of an ontogenetically fixed and shared phyletic pathway (a preset internal
channel with a vengeance).
- Charles Otis Whitman, a great early 20th century American naturalist,
developed the most congenial auxiliary theory (to Darwinism) of orthogenesis in
his extensive work on the evolution of color patterns in Darwin's own favorite
organism, the domestic pigeon. Whitman argued that domestic pigeons in
particular, and dove-like birds in general, followed a strong channel of internal
predisposition leading in one direction from checkers to bars, and eventually to the
obliteration of all color. (Darwin, by interesting contrast, argued for a reverse
tendency from bars to checkers, but also held, as his basic theory obviously
implies, that selection largely determines any particular event and that no internal
predisposition can trump the dictates of immediate function.) - In his 1894 book on Materials for the Study of Variation (where he coined
the term homeosis), William Bateson presented an extensive catalog of cases in
discontinuous variation among individuals in a population and between
populations of closely related organisms. He used these examples to develop a
formalist theory of saltational evolution, strongly opposed to the adaptationist
assumptions of Darwinian accounts. (Bateson's acerbic criticisms of adaptationist
scenario-building and story-telling in the speculative mode emphasize a common
linkage between structuralist preferences for mechanical explanation, and distaste
for the adaptationist assumption that functional necessity leads and the evolution of
form follows.) Although Bateson coined the term genetics, his personal
commitment to a "vibratory" theory of heredity, based on physical laws of classical
mechanics—an intuition that he could never "cash out" as a testable theory—
prevented his allegiance to the growing influence of Mendelian principles. - Hugo de Vries, the brilliant Dutch botanist who understood the logic of
selectionism so thoroughly and acutely (but largely in contrast with the only other
biologists, Weismann and Darwin himself, who also grasped all the richness and
range of implications, but with favor), developed a saltational theory of evolution,
but explicitly denied any predisposition of lineages to follow internal channels of
constraint. (He thus showed the potential independence of the frequently linked
formalist themes of channeling and saltation, a conjunction espoused by Bateson
and Goldschmidt for example, but denied in the other direction by Whitman, who
favored channeling but denied saltation by supporting a gradualist theory of
orthogenetic change.) This fascinating scholar regarded Darwin as his intellectual
hero and never forgot the kindness and encouragement conveyed by his mentor
and guru during
68 THE STRUCTURE OF EVOLUTIONARY THEORY