362 THE STRUCTURE OF EVOLUTIONARY THEORY
Each principal "law" of channeled variation identifies a putative ontogenetic
pathway, and therefore indicates the status of individual growth as the primary
determinant of evolutionary direction. Eimer includes in his list:
- As an overarching principle, the biogenetic law of recapitulation, which
specifies that the sequence of terminally added features in phylogeny shall, through
acceleration of development, become the ontogenetic channel of future changes.
But what regularities specify the character of these terminal additions? - The invariant series of changes in color markings from longitudinal stripes,
to spots, to transverse stripes, and finally (in most cases, when intensification
occurs) to darker and more uniform coloring. Today, we may be surprised and
puzzled (as, by the way, were many scientists at the time, for example Whitman,
- by Eimer's decision to present so apparently particular and contingent a
sequence as not only effectively universal, but also as the major specific rule of
channeling stressed in all his publications. Eimer first enunciated this principle in
his early work on lizards. The doctrine then became the foundation for his most
important study on coloration of butterfly wings (the focus of the final volume
(1897) of his treatise on orthogenesis and evolutionary theory). Eimer's specific
claims for butterflies did not gain a wide following, as many naturalists recognized
the circular character of his argument. (He assumed the law of longitudinal striping
spots transverse striping a priori and then used this principle to establish
"phyletic" sequences of living species with no other criterion of cladistic order).
- "The law of wave-like evolution, or law of undulation" (1890, p. 29). New
characters appear at particular parts of the body—almost always the posterior
end—and then pass forward during growth. A series of progressive waves may
sweep over the body during a single ontogeny. This law, apparently so arbitrary
and riddled with exceptions, also met with little favor, even among fellow
orthogeneticists. Whitman (1919), for example, accepted the notion of spatial
"waves" in ontogeny as channels of variation, but argued that progressive color
variation passed from front to back in pigeons, in direct opposition to Eimer's
pathway. (A "rational" basis for spatial waves could be sought in the biogenetic
law, as older parts of the body should act as the source for new phyletic features
added terminally. But the posterior end of an animal may be either old or young
depending on the body's mode of growth.) - "The law of male preponderance." In Eimer's words (1890, p. 28): "that
where new characters appear, the males, and indeed the vigorous old males,
acquire them first, that the females on the contrary remain always at a more
juvenile lower stage, and that the males transmit these new characters to the
species." This principle could claim a rationale beyond simple sexism (though this
social context should not be disregarded as a source either), for male
preponderance followed from the general theme behind all Eimer's channels— the
biogenetic law. If, as most biologists believed in Eimer's time, males tend to move
beyond terminal female stages in a common ontogenetic channel,