lution in modern science. In particular, as Chapter 2 will discuss in detail, Darwin
converted evolution from untestable speculation to doable science by breaking
through the old paradox (as embedded most prominently in Lamarck's system) of
contrasting a palpable force of small-scale change that could do little in extension,
with a basically nonoperational (and orthogonal) mechanism of large-scale change
putatively responsible for all the interesting patterns of life's history, but
imperceptible and untestable from the uniformitarian study of modern organisms.
By claiming that the small-scale mechanics of modern change could, by
extension, explain all of evolution, Darwin opened the entire field to empirical
study. And yet, as Hegel and so many other students of change have noted,
progress in human (and other) affairs tends to spiral upwards in cycles of proposal
(thesis), then countered by opposition (antithesis), and finally leading to a new
formulation combining the best aspects of both competitors (synthesis). Darwin's
thesis established evolution as a science, but his essential commitments, as
expressed in the three legs of his necessary logical tripod (or the three branches of
his conceptual tree or coral, as in the alternate metaphor of Fig. 1-4), eventually
proved too narrow and confining, thus requiring an antithesis of extension and
reformulation on each branch, and leading—or so this book maintains as a central
thesis of its own—to a still newer and richer synthesis expressing our best current
understanding of the structure of evolutionary theory.
In fact, and to repeat my summary in this different form, one might
encapsulate the long argument of this book in such a Hegelian format. Pre-
Darwinian concepts of evolution remained speculative and essentially
nonoperational, largely because (see Chapter 3) they fell into the disabling paradox
of contrasting an effectively unknowable large-scale force of cosmic progress
against an orthogonal, palpable and testable small-scale force that could generate
local adaptation and diversity, but that couldn't, in principle, explain the
macroevolutionary pattern of life. Then Darwin, in his thesis (also an antithesis to
these earlier sterile constructions), brilliantly argued that the putative large-scale
force did not exist, and that all evolution could be explained by upward
extrapolation from the small-scale force, now properly understood as natural
selection. In a first stage of debate during the late 19th and early 20th centuries
(Chapters 3-6), most critiques of Darwinism— one might designate them as a first
round of ultimately destructive antitheses—simply denied sufficient agency,
efficacy and range to natural selection, and reasserted the old claim of duality, with
selection relegated to triviality, and some truly contrary force sought as the
explanation for major features of evolution. Strict Darwinism eventually fended off
these destructive critiques, reasserted itself in the triumphant, and initially (and
generously) pluralistic form of the Modern Synthesis, but eventually calcified into
a "hardened" version (Chapter 7).
Then, in a strikingly different, and ultimately fruitful, second round of
antitheses, a renewed debate about central theoretical issues arose during the last
three decades of the 20th century, and reshaped the field by recognizing
24 THE STRUCTURE OF EVOLUTIONARY THEORY