The Fruitful Facets of Galton's Polyhedron 395
devised and supported by such brilliant men as Darwin and de Vries, must in-
evitably hold at least partial value—and he sought a fruitful union of these systems
with his own favored theory of orthogenesis. "Natural selection, orthogenesis, and
mutation appear to present fundamental contradictions, but I believe that each
stands for truth, and that reconciliation is not distant" (1919, p. 10).
We all know that the theories of de Vries and Darwin eventually reached
peace through a recognition that micromutations could act as the source of
isotropic Darwinian variation. We regard this fusion as the basis for the Modern
Synthesis. A similar and vital task has only begun in our time, but we now live in
an age struggling for further union—to join the success of this Modern Synthesis
with neglected structuralist and formalist themes of developmental constraint and
channeled variation (see Chapters 10 and 11 for my effort in this direction).
Whitman surely erred in interpreting a channel of variation— a pathway of
potential evolution in either direction—as a one-way street of inevitable change.
(The reinterpretation of orthogenetic "one way streets" as "channels" of preferred
variability establishes a key "translation" for updating this older and valuable
literature into relevance for our modern debates. I also strongly suspect, in
opposition to both Darwin and Whitman, that ancestral pigeons were neither two-
barred nor checkered, but both. After all, ancestors exist as populations, not
archetypes. Both states persist in continuous gradation within many modern
populations of pigeons—and this entire channel may well have been expressed
among variable adults in ancestral populations.)
However, Whitman's notion that selection does not encounter a full range of
isotropic variation, but must work instead with material strongly biased by internal
constraint, may supply a key theme for an even higher synthesis of external and
internal forces—a theory that will preserve a Darwinian core, but finally and
properly incorporate the formalist themes, advocated as central to evolutionary
understanding by many of the finest biologists from the very beginning of our
profession. Whitman succinctly stated the basis of this synthesis, but we are only
now beginning to learn enough about genetics and development to vindicate his
hunches: "Natural selection waits for opportunities to be supplied, not by
multifarious variation or orderless mutation, but by continuous evolutional
processes advancing in definite directions" (1919, p. 13). *
*We should give the last word, if only in a footnote, to the ever-perceptive T. H.
Huxley, Darwin's stoutest supporter, but an incisive critic for several aspects of natural
selection in its strict form. Whitman cited this passage from Huxley (Darwiniana) as an
epigraphic quotation to one of his articles on orthogenesis (1919, p. 64): "But the causes
and conditions of variation have yet to be thoroughly explored, and the importance of
natural selection will not be impaired even if further inquiries should prove that
variability is definite and is determined in certain directions rather than in others, by
conditions inherent in that which varies. It is quite conceivable that every species tends to
produce varieties of a limited number and kind and that the effect of natural selection is
to favor the development of some of these, while it opposes the development of others
along their predetermined lines of modification."