The Structure of Evolutionary Theory

overlying public structure. A framework, on the other hand, defines the basic form
and outline of the public structure itself. Thus, the two men conjure up very
different pictures in their crystal balls. Falconer expects that the underlying
evolutionary principle of descent with modification will persist as a factual
foundation for forthcoming theories devised to explain the genealogical tree of life.
Darwin counters that the theory of natural selection will persist as a basic
explanation of evolution, -even though many details, and even some subsidiary
generalities, cited within the Origin will later be rejected as false, or even illogical.
I stress this distinction, so verbally and disarmingly trivial at a first and
superficial skim through Falconer's and Darwin's words, but so incisive and
portentous as contrasting predictions about the history of evolutionary theory,
because my own position—closer to Falconer than to Darwin, but in accord with
Darwin on one key point—led me to write this book, while also supplying the
organizing principle for the "one long argument" of its entirety. I do believe that
the Darwinian framework, and not just the foundation, persists in the emerging
structure of a more adequate evolutionary theory. But I also hold, with Falconer,
that substantial changes, introduced during the last half of the 20th century, have
built a structure so expanded beyond the original Darwinian core, and so enlarged
by new principles of macroevolutionary explanation, that the full exposition, while
remaining within the domain of Darwinian logic, must be construed as basically
different from the canonical theory of natural selection, rather than simply
extended.
A closer study of the material basis for Falconer and Darwin's metaphors—
the Duomo (or Cathedral) of Milan—might help to clarify this important
distinction. As with so many buildings of such size, expense, and centrality (both
geographically and spiritually), the construction of the Duomo occupied several
centuries and included an amalgam of radically changing styles and purposes.
Construction began at the chevet, or eastern end, of the cathedral in the late 14th
century. The tall windows of the chevet, with their glorious flamboyant tracery,
strike me as the finest achievement of the entire structure, and as the greatest
artistic expression of this highly ornamented latest Gothic style. (The term
"flamboyant" literally refers to the flame-shaped element so extensively used in the
tracery, but the word then came to mean "richly decorated" and "showy," initially
as an apt description of the overall style, but then extended to the more general
meaning used today.)
Coming now to the main point, construction then slowed considerably, and
the main western facade and entrance way (Fig. 1-1) dates from the late 16th
century, when stylistic preferences had changed drastically from the points, curves
and traceries of Gothic to the orthogonal, low-angled or gently rounded lintels and
pediments of classical Baroque preferences. Thus, the first two tiers of the main
(western) entrance to the Duomo display a style that, in one sense, could not be
more formally discordant with Gothic elements of design, but that somehow
became integrated into an interesting coherence. (The third tier of the western
facade, built much later, returned to a "retro" Gothic style, thus suggesting a
metaphorical reversal of phylogenetic conventions, as
4 THE STRUCTURE OF EVOLUTIONARY THEORY