scope, or the extrapolatability of microevolution to explain all patterns in
geological time—and is therefore the aspect of gradualism that punctuated
equilibrium refutes (for punctuated equilibrium questions Darwin's uniformitarian
and continuationist beliefs, but not his mechanism of natural selection). This
parsing of three distinctly different forms of gradualism, all embraced by Darwin
for different reasons, alleviates the misunderstanding behind some unfortunate
terminological wrangles without substance that have generated much heat (but
little light) in recent debates.
- The adaptationist program as a primary strategy of research emerges as the
third major implication of advocating natural selection as the primary creative
force in evolutionary change—for this Darwinian style of evolution must proceed
step by step, with each tiny increment of change rendering organisms better
adapted to alterations in local environments. To summarize all the key implications
of this second theme of efficacy, the creativity of natural selection makes
adaptation central, isotropy of variation necessary, and gradualism pervasive. - Restriction of agency to the organismal level, and assertions of selection's
creativity, set a biological basis for the third essential claim of Darwinian logic—
selection's scope, or the argument that this incremental and gradualistic style of
microevolution can, by smooth extrapolation through the immensity of geological
time, build the full extent of life's anatomical change and taxonomic diversity by
simple accumulation. I focus my shorter discussion of this third essential theme not
upon biological needs (already covered in the first two themes), but upon the
requirement for similar gradualistic styles of change in the geological stage that
must present the evolutionary play—particularly in Darwin's embrace of Lyellian
uniformity, and his denial of catastrophism (through arguments about the
imperfection of the fossil record to allay the literal appearance of such rapidity in
geological data), for even a fully consistent, intellectually sound, and operationally
potent theory will not regulate actual events if surrounding conditions debar its
operation. - I use Kellogg's brilliant approach to the evaluation of Darwinian theory
(published in 1907 in anticipation of centennial celebrations for Darwin's birth and
the sesquicentenary of the Origin) to distinguish alternatives that deny the
fundamental postulate of selection's creativity from auxiliaries that enlarge,
adumbrate, or reformulate the theory of natural selection in basically helpful and
consistent ways. I show that Darwinism may be epitomized by its three essential
claims of agency, efficacy, and scope—and that the history of debate has always
centered upon these themes, with critiques focusing upon destructive alternatives
or constructive auxiliaries. I argue, as the major thesis of this book, that modern
debates have developed important and coherent auxiliary critiques on all three
branches of essential Darwinian logic, and that these debates may lead to a
fundamentally revised evolutionary theory with a retained Darwinian core.
Chapter 3: Seeds of hierarchy- Nearly all scientific revolutions originate as replacements and refutations of
62 THE STRUCTURE OF EVOLUTIONARY THEORY