sideration of major evolutionary concepts that still bear the originating stamp of a
Victorian scientific context strongly committed to unidirectional, single-level and
deterministic views of natural causality—subtly controlling concepts that many
scientists would now label as limiting and outmoded.
Although the next few paragraphs will be the most vague and impressionistic
(I trust) of the entire book, I venture these ill-formulated statements about Zeitgeist
because I feel that something important lurks behind my inability to express these
inchoate thoughts with precision. I argue above (page 14) that the key concerns of
the three essential branches of Darwinian logic might be identified as agency,
efficacy and scope of natural selection. In each of these domains, I believe, the
revised structure of evolutionary theory, as presented in this book, might be
characterized as expansion and revision according to a set of coordinated
principles, all consonant with our altered Zeitgeist vs. the scientific spirit of
Darwin's own time. The modern revision seeks to replace Darwin's unifocal theory
of organismic selection with a hierarchical account (leg one); his unidirectional
theory of adaptational construction in the functionalist mode with a more balanced
interaction of these external causes, treating internal (or structural) constraints
primarily as positive channels, and not merely as limitations (leg two); and his
unilevel theory of micro-evolutionary extrapolation with a model of distinctive but
interacting modes of change, each characteristic for its tier of time. In short, a
hierarchy of interacting levels, each important in a distinctive way, for Darwin's
single locus; an interaction of environmental outsides with organic insides for
Darwin's single direction of causal flow; and a set of distinctive temporal tiers for
Darwin's attempt to situate all causality in the single microevolutionary world of
our own palpable moments.
I do sense a common underlying vision behind all these proposed reforms.
Strict Darwinism, although triumphant within mid 20th century evolutionary
theory, embodied several broad commitments (philosophical or metatheoretical, in
the technical sense of these terms), more characteristic of 19th than of 20th century
thought (and, obviously, not necessarily wrong, or even to be discounted, for this
reason—as nothing can be more dangerous to the progress of science than winds of
fashion, and we do, after all, learn some things, and develop some fruitful
approaches, with validity and staying power well beyond their time of origin and
initial popularity). Some aspects of Darwin's formulation broke philosophical
ground in a sense quite consonant with our modern Zeitgeist of emphasis upon
complexity and interaction—particularly, Darwin's focus on the interplay of
chance and necessity in sources of variation vs. mode of selection. Indeed, Darwin
paid the usual price for such innovation in the failure of nearly all his colleagues,
even the most intellectually acute, to grasp such a radical underlying philosophy.
But, in many commanding respects, Darwinism follows the norms of favored
scientific reasoning in his time.
The logic of Darwin's formulation rests upon several preferences in scientific
reasoning more characteristic of his time than of ours—preferences that
Defining and Revising the Structure of Evolutionary Theory 31