adaptationist optimality for individualized features of anatomy—a theme that he
epitomized as "correlations of growth." But he developed an explicit framework
and rationale, most thoroughly discussed not in the Origin but in his longest 1868
book on The Variation of Animals and Plants Under Domestication, that relegated
such formalist effects to a clearly subservient and secondary status, compared with
natural selection and adaptation, in evolutionary causality.
Chapter 5: Channels and saltations in post-Darwinian formalism- Galton's Polyhedron, the metaphor and model devised by Darwin's brilliant
and eccentric cousin Francis Galton, and then fruitfully used by many evolutionary
critics of Darwinism, including St. George Mivart, W. K. Brooks, Hugo de Vries,
and Richard Goldschmidt, clearly expresses the two great, and both logically and
historically conjoined, themes of formalist (or structuralist, or internalist, in other
terminologies) challenges to functionalist (or adaptationist, or externalist) theories
in the Darwinian tradition. This model of evolution by facet-flipping to limited
possibilities of adjacent planes in inherited structure stresses the two themes—
channels set by internal constraint, and evolutionary transition by discontinuous
saltation—that structuralist alternatives tend to embrace and that pure Darwinism
must combat as challenges to basic components of its essential logic (for channels
direct the pathways of evolutionary change from the inside, albeit in potentially
positive and adaptive ways, even though some external force, like natural
selection, may be required as an initiating impulse; whereas saltational change
violates the Darwinian requirement for selection's creativity by vesting the scope
and direction of change in the nature and magnitude of internal jumps, and not in
sequences of adaptive accumulations mediated by natural selection at each step). - Orthogenesis, as a general term for evolutionary directionality along
channels of internal constraint, rather than external pathways of natural selection,
existed in several versions, ranging from helpful auxiliaries to Darwinism, to
outright alternatives that denied any creative potency to selection. Theodor Eimer,
who coined the term orthogenesis, presented a middle version that tried to integrate
internal channels of orthogenesis with external pathways of functionalist
determination. But Eimer defended Lamarckian mechanics for his functionalism,
thus leading him to oppose natural selection (he spoke of the Ohnmacht, or
"without power," of selection, contrasted with Weismann's Allmacht, or "all
power") despite his pluralistic linkage of formalist and functionalist explanations. - The orthogenetic theory of the late 19th century American paleontologist
Alpheus Hyatt embodied maximal opposition to natural selection, and must be
viewed as alternative, rather than auxiliary, to Darwinism. Hyatt conceived the
pathway of ontogeny, modified only by heterochronic changes permitted under the
biogenetic law, as the internal directing channel that natural selection could tweak,
but not derail. Illustrating the influence of theory over perception, Hyatt found
several parallel lineages of snails, running along
Defining and Revising the Structure of Evolutionary Theory 67