Chapter 2, and the development of the totality. Now, and most sheepishly, I add
two more, for a fractal total of five—the listed abstract, in pure "book order," of
this section, and (God help us) the epitome of this epitome, presented now to
introduce and guide the list.
I develop my argument throughout this book by asserting, first, that the
central logic of Darwinism can be depicted as a branching tree with three major
limbs devoted to selection's agency, efficacy and scope. Second, that Darwin,
despite his heroic and explicit efforts, could not fully "cash out" his theory in terms
of the stated commitments on each branch—and that he had to allow crucial
exceptions, or at least express substantial fears, in each domain (admitting species
selection to resolve the problem of diversity; permitting an uncomfortably large
role for formalist correlations of growth as compromisers of strict adaptationism;
expressing worry that mass extinction, if more than an artifact of an imperfect
fossil record, would derail the extrapolationist premise of his system). Third, that
the subsequent history of evolutionary debate has focused so strongly upon the key
claims of these three essential branches that we may use engagement with them as
a primary criterion for distinguishing the central from the secondary when we need
to gauge the importance of challenges to the Darwinian consensus. Fourth, that we
should not be surprised by the prominence of these three themes, for they embody
(in their biological specificity) the broadest underlying issues in scientific expla-
nation, and in the nature of change and history: levels of structure and causality,
rates of alteration, directions of causal flow, the possibility of causal unification by
reduction to the lowest level vs. autonomy and interaction of irreducible levels,
punctuational vs. gradual change, causal and temporal tiering vs. smooth
extrapolation. Fifth, that the most interesting and important debates in our
contemporary science continue to engage the same three themes, thus requiring the
vista of history to appreciate the continuity and logical ordering that extends right
back to Darwinian beginnings. Sixth, that our best modern understanding of the
structure of evolutionary theory has reversed the harmful dichotomization of
earlier debates (Darwinian fealty vs. destructive attempts to trivialize or overturn
the mechanism of selection) by confronting the same inadequacies of strict
Darwinism, but this time introducing important additions and revised formulations
that preserve the Darwinian foundation, but build a theory of substantial expansion
and novelty upon a retained selectionist core.
This logic and development may be defended as tolerably impersonal and
universal, but any book of this length and complexity, and of so idiosyncratic a
style and structure, must also own its authorial singularities. The Structure of
Evolutionary Theory emerges, first of all, from my professional focus as a
paleontologist and a student of macroevolution, defined, as explained on page 38,
as descriptive phenomenology prior to any decision about the need for distinctive
theory (my view) or the possibility of full subsumption under microevolutionary
principles (the view of Darwin and the Modern Synthesis). The contingency of
history guarantees that any body of theory will underdetermine important details,
and even general flows, in the realized
Defining and Revising the Structure of Evolutionary Theory 55