380 THE STRUCTURE OF EVOLUTIONARY THEORY
as these, that an animal found to repeat the stages of another animal of a closely
allied species in the young, with the addition of new characteristics in the adult,
may be considered to be either a lineal descendant of that species, or of some form
common to both; that in such cases as these, whether the form or species occur
mixed on the same level, or on different levels, there is but one natural
arrangement" (1880, p. 8).
If recapitulation entered the argument as an a priori assumption, then so did
the cognate notion (in Hyatt's mind at least) of racial life cycles. Hyatt assumed the
very phenomenon he hoped to prove when he built his phyletic sequences in the
absence of stratigraphic resolution, often from specimens on the same bedding
plane. He resolved all violations of stratigraphic order by dictates of the "old age"
theory. For example, both Hyatt and Hilgendorf regarded P. oxystomus as a derived
branch of the main stock. But Hyatt interpreted this species as the base of an
extensive progressive series, built upon variation within a single bedding plane
because he could establish no empirical continuity to still higher stratigraphic
levels. Hyatt's preferred order helped his argument immensely—for the idea of
parallel yet non-synchronous lineages strongly supported his claim for internal
necessity, not environmental entrainment, in the unfolding of phyletic stages. But
he presented no evidence beyond the ordering power of the preconceived theory
itself!
In a second example that engendered bitter debate with the followers of
Hilgendorf, Hyatt claimed additional evidence for non-synchronous parallelism by
finding the most advanced specimens of P. trochiformis (the acme of the main
progressive lineage) in the lowest stratigraphic levels—leading to the assertion that
this entire lineage unfolded with great rapidity (and providing more evidence for
internal programming since other lineages would then be evolving much more
slowly, and Hyatt could therefore identify differential phyletic vigor, rather than
variation in environmental pressure, as the cause for disparities in evolutionary
rate). But other researchers could only find P. trochiformis at high stratigraphic
levels (Hyatt's lower specimens may have eroded from upper levels and washed
down)—and therefore interpreted this lineage as evolving much more slowly.
If Hyatt maintained such overweening faith in the validity of his orthogenetic
theory of ontogenetic programming, we can scarcely be surprised that he also read
the supposed empirics of the Steinheim planorbids as a disproof of Darwinism—
hence Darwin's negative response in receiving the monograph (see p. 372). Hyatt
attempted to specify both the potential and the limits of natural selection for the
Steinheim planorbids—and the restrictions overwhelmed the possibilities.
Following the usual formalist critique of selection's creativity, Hyatt allowed that
selection might explain why four lineages, rather than fewer or many more,
became established, and why they continued to propagate. The origin of four
lineages in the Steinheim lake, Hyatt tells us:
... appears therefore to be perfectly well accounted for by Darwin's theory
of natural selection. In no other way can we possibly account for the