The Fruitful Facets of Galton's Polyhedron 353
vague theoretical notion invented to oppose Darwin's principle of undirected
variation, then the usual charge of vacuousness might apply. But all leading
orthogeneticists, as my three case studies will demonstrate, identified a primary
channel fully consistent with a late 19th century biological consensus. Haeckel's
biogenetic law had become widely accepted as the preeminent principle for tracing
phylogeny (Gould, 1977b). This law of recapitulation required that new
evolutionary features be added to the ends of previous ontogenies, and that early
stages of development be continually speeded up (law of acceleration) to provide
room for these additions; adult stages of ancestors therefore migrated "backwards"
in ontogeny to become juvenile features of descendants. This principle validated a
primary ontogenetic channel as the major determinant of highly constrained
evolutionary variability. Features consistent with established ontogenetic
trajectories—as additions (by hypermorphosis) or regressions (by secondary
slowing of developmental rate)— might easily arise as new evolutionary variants.
Other configurations, even if potentially useful to organisms, might never arise in
such a constrained system. In short, ontogeny itself served as the primary channel
of constrained variation in orthogenetic theory.
- The "hard version" of orthogenesis (held by some proponents, including
Hyatt in my case studies) of inexorable one-way streets leading straight to
extinction by degeneration of form compels little attention today (and enjoyed little
support even in its own time). But the "softer" version of two-way channels—
furrows of constrained variation that provided biased material to natural selection,
but could not drive a trend to extinction all by itself and against Darwinian
forces—expresses a primary and enduring theme of a formalist and structuralist
biology that should still engage our close attention.
To explicate orthogenesis, I turn once again to Vernon Kellogg (1907), author
of the finest book on varieties of evolutionary theories and their distinctions (in a
time of maximum disaffection with Darwinism and general agnosticism about
alternatives). As discussed on pages 163-169, my framework for this book owes
much to Kellogg's argument that Darwinism should be defined by a meaningful
essence of minimal commitments—and that other notions can therefore be
classified as basically helpful ("auxiliary" in his terminology) or contrary
("alternative").
Kellogg identified three major "alternatives" to natural selection—one as
functionalist as Darwinism, but offering a different explanation of adaptation
(Lamarckism), and the other two as structuralist denials that adaptation must guide
the origin of new species (orthogenesis, and heterogenesis or saltationism in de
Vries's macromutational style). But Kellogg showed particular sensitivity to the
nuances, shadings and subtleties that arguments about relative frequency always
impart to natural history. He clearly stated that the logic of all three alternatives
stands squarely against natural selection if we argue for prevailing strength of
effect and relative frequency: "All of these theories offer distinctly substitutional
methods of species forming" (1907, p. 262).
However, Kellogg also recognized that "milder" versions might be seen