352 THE STRUCTURE OF EVOLUTIONARY THEORY
mechanical rules of embryological development on the other. The word literally
means "straight (line) generation," but the term never bore a merely descriptive
meaning, and all evolutionists understood the wider import. Orthogenesis denotes
the claim that evolution proceeds along defined and restricted pathways because
internal factors limit and bias variation into specified channels. In this key sense,
orthogenesis must be regarded as a formalist theory, standing against the central
Darwinian principle that natural selection imparts direction by shaping isotropic
variation (and doesn't only act in a negative and subsidiary way to eliminate the
unfit while some other process creates the fit). (Evolutionists recognized, of
course, that natural selection could also produce a directional anagenesis—first
called "orthoselection" by Ludwig Plate—and that claims for orthogenesis must
therefore demonstrate a causal basis for internal channeling beyond the power of
natural selection to shape, and not only record the simple pattern of monotonic
change itself).
Later on, after the Modern Synthesis congealed, and a latter day Darwinian
consensus needed to recruit some whipping boys from the past, orthogenesis
became a convenient foil for illustrating the bad old days of failure to grasp
selection's power. Ever since, most textbook one-liners have dismissed
orthogenesis as a theistic remnant operating as a mild pollutant within science, an
almost mystical theory of arcane and inexorable direction. I shall present the
arguments of three prominent supporters—G. H. T. Eimer, A. Hyatt, and C. O.
Whitman—to explicate orthogenesis as a viable and well-wrought formalist
alternative (or supplement) to Darwinism at a time when natural selection could
muster no compelling defense. But in hopes of encouraging a more sympathetic
hearing, I begin with three points raised to allay our conventional misconceptions
in a more general way.
- Some prominent non-Darwinians may justly be designated as "theistic
evolutionists"—St. George Mivart and Pierre Teilhard de Chardin, for example.
But orthogenesis does not fall into this category. Rather, and entirely to the
contrary, all leading orthogeneticists insisted vociferously that their arguments for
internal directionality included no teleological or theistic component. Most leading
orthogeneticists held strictly mechanistic views in the mainstream of the highly
deterministic late 19th century scientific consensus. They argued that internal
channels arose as products of conventional, physical causes, based upon properties
of hereditary and developmental systems. (These properties may have been
unknown, hence "mysterious" in the vernacular sense, but certainly not spiritual or
teleological.) In stating claims for predictability of phyletic directions, and for
parallelism of numerous independent lineages constrained by the same internal
mechanics, most orthogeneticists considered themselves in better tune with the
physical and deterministic spirit of the age, whereas Darwinians fell into
disharmony by committing themselves to undirected variation and unpredictable
contingency of change. Moreover, the orthogeneticists argued, how could a charge
of theistic progressionism be leveled when orthogenetic channels drove lineages to
extinction as often as to complexity? - If the concept of internally constrained channels only represented a