364 THE STRUCTURE OF EVOLUTIONARY THEORY
natural growth, whose operations are changed, intensified, or diminished to
a certain extent by the stress of adaptation, and may also at times be
entirely restrained.(Linguistic choices can be highly illuminating. Note how Eimer refers to
adaptation as a "stress" rather than a determining cause—that is, a push from the
outside that can, at most, speed up, slow down, or change in minor ways the
primary pathway of internal direction.)
Second, although adaptationist guesses can be formulated for the observed
channels, formalist alternatives also exist, and seem eminently more reasonable.
The law of undulation from back to front, for example, only reflects the metameric
growth of many animals. The back segments form last, and late stages, under the
biogenetic law, develop progressive characters (1890, pp. 60, 69).
In sum, orthogenesis derails Darwinian functionalism by denying the crucial
requirement for undirected variability. "The variation of species takes place not in
all kinds of directions irregularly, but always in definite directions, and indeed in
each species in a given time in only a few directions" (1890, p. 20). Ultimately,
Eimer rejected Darwinism for the most common of all 19th century reasons—the
critique of "creativity"—for he clearly understood the deathblow that such
powerfully channeled and limited variation would deal to Darwinian hopes for
awarding a dominant relative frequency to natural selection in creating
evolutionary change: "Natural selection becomes weak [ohnmdchtig] thereby. It
cannot be depicted as an active major cause [Hauptmittel] in the transformation of
forms; at most, it can be an auxiliary cause [Nebenmittel] of such transformation,
as it can only perfect what orthogenesis ordains" (1897, pp. 14-15).
The metaphors and images chosen by scientists to illustrate their complex
views often provide our best insight into their relative weighting of interacting
forces and foci. Eimer developed what he and others considered a "liberal" or a
"compromise" version of orthogenesis, where internal forces of directed variation
do not determine the entire shape and rate of phylogeny (as in Hyatt's more
extreme views), but rather work in balance with environmental determinants—a
model of external triggers and choosers for a strictly limited number of internally
set pathways. This balanced view, as noted above, might have awarded important
space to Darwinian functionalism as an external force—except for Eimer's
particular commitment to Lamarckian causes as primary determinants of the
external component, with selection acting only as an auxiliary force, largely
confined to the negative role of eliminating the unfit.
Eimer summarized these weightings in a metaphor that compared evolution
with the migration of a population. The direction of movement represents the
orthogenetic pathway, the dominant cause of the entire process. External forces of
environment act primarily in finetuning this predetermined direction. Adaptation
may play an important role, but the Lamarckian inheritance of acquired characters
trumps Darwinian factors in this realm of functional