exciting subject within the ever changing and ever expanding world of modern
science.
The Structure of Evolutionary Theory: Revising the Three Central Features
of Darwinian Logic
In the opening sentence of the Origin's final chapter (1859, p. 459), Darwin
famously wrote that "this whole volume is one long argument." The present book,
on "the structure of evolutionary theory," despite its extravagant length, is also a
brief for an explicit interpretation that may be portrayed as a single extended
argument. Although I feel that our best current formulation of evolutionary theory
includes modes of reasoning and a set of mechanisms substantially at variance with
strict Darwinian natural selection, the logical structure of the Darwinian foundation
remains remarkably intact—a fascinating historical observation in itself, and a
stunning tribute to the intellectual power of our profession's founder. Thus, and not
only to indulge my personal propensities for historical analysis, I believe that the
best way to exemplify our modern understanding lies in an extensive analysis of
Darwin's basic logical commitments, the reasons for his choices, and the
subsequent manner in which these aspects of "the structure of evolutionary theory"
have established and motivated all our major debates and substantial changes since
Darwin's original publication in 1859.1 regard such analysis not as an antiquarian
indulgence, but as an optimal path to proper understanding of our current
commitments, and the underlying reasons for our decisions about them.
As a primary theme for this one long argument, I claim that an "essence" of
Darwinian logic can be defined by the practical strategy defended in the first
section of this chapter: by specifying a set of minimal commitments, or broad
statements so essential to the central logic of the enterprise that disproof of any
item will effectively destroy the theory, whereas a substantial change to any item
will convert the theory into something still recognizable as within the Bauplan of
descent from its forebear, but as something sufficiently different to identify, if I
may use the obvious taxonomic metaphor, as a new subclade within the
monophyletic group. Using this premise, the long argument of this book then
proceeds according to three sequential claims that set the structure and order of my
subsequent chapters:
- Darwin himself formulated his central argument under these three basic
premises. He understood their necessity within his system, and the difficulty that
he would experience in convincing his contemporaries about such unfamiliar and
radical notions. He therefore presented careful and explicit defenses of all three
propositions in the Origin. I devote the first substantive chapter (number 2) to an
exegesis of the Origin of Species as an embodiment of Darwin's defense for this
central logic. - As evolutionary theory experienced its growing pains and pursued its
founding arguments in the late 19th and early 20th centuries (and also in
Defining and Revising the Structure of Evolutionary Theory 13