The first theme of agency: Darwin's commitment to the organismal level as
the effectively exclusive locus of natural selection occupies a more central, and
truly defining, role than most historians and evolutionists have recognized.
Invocation of this most reductionistic locus then available (in ignorance of the
mechanism of inheritance) embodies the intellectual radicalism of Darwin's
theory—using Adam Smith to overturn Paley, and holding that all higher-order
harmony, previously attributed to divine intention, arises only as a side-
consequence of selfish "struggle" for personal advantage at the lowest organismal
level. Darwin devoted far more of the Origin to defending this organismal locus
than most exegetes have acknowledged, particularly in centering his only two
chapters on specific difficulties in natural selection (7 on Instinct and 8 on
Hybridism) to resolutions provided by insistence upon organismal agency—
explaining the establishment of adaptive sterile castes in social insects by selection
upon queens as individuals, and resolving sterility in interspecific crosses as an
unselected sequel of differences accumulated by organismal selection in each of
two isolated populations, rather than as a direct result of higher-level species
selection, as Wallace affirmed and as Darwin strove mightily and consciously to
avoid. We can also trace his struggle to affirm organismal exclusivity in his
reluctances, underplayings and walling off (as unique and unrepeated elsewhere in
nature) of the one exception (for human altruism) that the logic of his system
forced upon his preferences.
For his defense of the second theme of efficacy—his assertion of natural
selection as the only potent source of creative evolutionary change—Darwin
recognized that his weak and negative force, although surely a vera causa (true
cause), could only play this creative role if variation met three crucial re-
quirements: copious in extent, small in range of departure from the mean, and
isotropic (or undirected towards adaptive needs of the organism). I would argue
that Darwin's most brilliant intellectual move lay in his accurate identification,
through the logical needs of his theory and not from any actual knowledge of
heredity's mechanism, of these three major attributes of variation—because he
recognized that natural selection could not otherwise operate as a creative force in
The Problem of History
Gradualism enters Darwin's system as another deductive intellectual
consequence of asserting that natural selection acts as the creative mechanism of
evolutionary change. Gradualism has three distinct meanings in Darwinian
traditions, with only the second (or intermediate) statement relevant to the central
assertion of selection's creativity. First, gradualism as simple historical continuity
of stuff or information underlies the basic factuality of evolution vs. creation, and
does not validate any particular mechanism of evolutionary change. Second,
gradualism as insensible intermediacy of transitional forms specifies the
Goldilockean "middle position" required by the mechanism of natural selection to
refute the possibility that saltational variation might engender creative change all at
once, thus relegating selection to a negative role of removing the unfit. Third,
gradualism as a geological claim for slowness and smoothness (but not constancy)
of rate plays a crucial role in the third theme (see point 10 of this list) of selection's
Defining and Revising the Structure of Evolutionary Theory 61
