changes). For, by the conventional rationale, the study of microevolution became
virtually nonoperational in paleontology—as one almost never found this
anticipated form of gradual change up geological sections, and one therefore had to
interpret the vastly predominant signal of stasis and geologically abrupt appearance
as a sign of the record's imperfection, and therefore as no empirical guide to the
nature of evolution. Second, I became increasingly disturbed that, at the higher
level of evolutionary trends within clades, the majority of well documented
examples (reduction of stipe number in graptolites, increasing symmetry of
crinoidal cups, growing complexity of ammonoid sutures, for example) had never
been adequately explained in the terms demanded by Darwinian convention—that
is, as adaptive improvements of constituent organisms in anagenetic sequences.
Most so-called explanations amounted to little more than what Lewontin and I,
following Kipling, would later call "just-so stories," or plausible claims without
tested evidence, whereas other prominent trends couldn't even generate a plausible
story in adaptationist terms at all.
As Eldredge and I devised punctuated equilibrium, I did use the theory to
resolve these two puzzles to my satisfaction, and each resolution, when finally
generalized and further developed, led to my two major critiques of the first two
branches of the essential triad of Darwinian central logic—so Oliver Sacks's
identification of punctuated equilibrium as central to my theoretical world holds,
although more as a starting point than as a coordinating focus. By accepting the
geologically abrupt appearance and subsequent extended stasis of species as a fair
description of an evolutionary reality, and not only as a sign of the poverty of
paleontological data, we soon recognized that species met all criteria for definition
and operation as genuine Darwinian individuals in the higher-level domain of
macroevolution—and this insight (by complex routes discussed in Chapter 9) led
us to concepts of species selection in particular and, eventually, to the full
hierarchical model of selection as an interesting theoretical challenge and contrast
to Darwinian convictions about the exclusivity of organismal selection. In this
way, punctuated equilibrium led to the reformulation proposed herein for the first
branch of essential Darwinian logic.
Meanwhile, in trying to understand the nature of stasis, we initially focused
(largely in error, I now believe) upon internal constraints, as vaguely represented
by various concepts of "homeostasis," and as exemplified in the model of Galton's
polyhedron (see Chapter 4). These thoughts led me to extend my doubts about
adaptation and the sufficiency of functionalist mechanisms in general—especially
in conjunction with my old worries about paleontological failures to explain cladal
trends along traditional adaptationist lines. Thus, these aspects of punctuated
equilibrium strongly contributed to my developing critiques of adaptationism and
purely functional mechanics on the second branch of essential Darwinian logic
(although other arguments struck me as even more important, as discussed below).
Nonetheless, and despite the centrality of punctuated equilibrium in
developing a broader critique of conventional Darwinism, my sources extended
40 THE STRUCTURE OF EVOLUTIONARY THEORY