The Fruitful Facets of Gabon's Polyhedron 373
why not propose the far simpler interpretation that these shortened ontogenies and
"degraded" adult forms represent adaptations to conditions of life that also
characterized early stages of the lineage. This stark contrast and mutual
incomprehension illustrate, in a striking manner, the difference between Hyatt's
formalist orthogenesis as an ultimate drive to phyletic death, and Darwin's
functionalism, with extinction as failure to adapt. Darwin wrote to Hyatt (in F.
Darwin, 1903, pp. 343-344): "With respect to degradation of species towards the
close of a series, I have nothing to say, except that before I arrived at the end of
your letter, it occurred to me that the earlier and simpler ammonites must have
been well adapted to their conditions, and that when the species were verging
towards extinction (owing probably to the presence of some more successful
competitors) they would naturally become readapted to simpler conditions."
Later in the same letter, Darwin pens the most famous line of this
correspondence—a lovely contrast between the contingency of environmentally
entrained adaptation and the predictability of "hardline" formalism as a theory of
internal necessity: "After long reflection I cannot avoid the conviction that no
innate tendency to progressive development exists" (in F. Darwin, 1903, volume 1,
p. 344).
Through the density of theoretical discussion in these letters, another theme
circulates. Hyatt expresses his plans to restudy one of the most famous
paleontological series of presumed stratigraphic continuity in an isolated setting:
the Miocene fresh-water planorbid pulmonates of the Steinheim lake in Germany
(then interpreted as a volcanic caldera, but now recognized as a meteor crater—see
Reif, 1976). The German paleontologist Hilgendorf had published an already
classical account in 1866, including one of the first genealogical diagrams to
reflect Darwin's new world order. Hyatt proposed a restudy and Darwin opined: "I
earnestly hope that you may visit Hilgendorf's famous deposit ... I most sincerely
wish you success in your valuable and difficult researches" (in F. Darwin, 1903, p.
344). Hyatt proceeded, and eventually provoked Darwin's last and bitter response
to his orthogenetic ideas by sending Darwin a copy of his monograph (1880) on
the Steinheim planorbids.
Hyatt's proposed phylogeny could hardly differ more from Hilgendorf's
original interpretation (Fig. 5-4). Where Hilgendorf drew a conventional branching
tree with a monophyletic root, Hyatt presented four lineages, separate at the base
and evolving in strict parallel. Such a striking difference should, in our
conventional view of scientific change, record Hyatt's improved observations at the
site. Hyatt did make some empirical changes (although we would have to view his
effort, in retrospect, as a continuity in steady state rather than an improvement over
Hilgendorf, for he corrected some errors but introduced just as many others). But
Hyatt's alterations primarily record the application of a different theory to the same
data. Iconography often provides a powerful guide to conceptual frameworks
because pictures frequently make explicit what our psyches fail to acknowledge in
the