Punctuated Equilibrium and the "Validation of Macroevolutionary Theory 923
theory first seriously proposed in 1980 and then strongly promoted by increasingly
firm evidence for bolide triggering of the late Cretaceous event, as an obvious
input from paleontology. I take pride in the role that punctuated equilibrium has
played as a spur for this larger intellectual transformation— for our 1972 proposal,
formulated at one level of biological change, provided some general guidelines,
definitions and terminology, and also provoked a good deal of interest in the
application of this general style of change to other fields of study and other levels
of causality. This extension has proceeded so far that some scientists and scholars
from other disciplines (see Gersick, 1991; Mokyr, 1990; Den Tex, 1990;
Rubinstein, 1995, for example) now use punctuated equilibrium as the general term
for this style of change (while we would prefer that punctuated equilibrium retain
its more specific meaning for the level of speciation, with punctuational change or
punctuationalism used for the generality).
Some recent mathematical work has explicitly tried to model punctuational
change at the level and phenomenology of our original theory. Rand and Wilson
(1993, p. 137), for example, following Rand et al.'s (1993) "general mathematical"
model for "Darwinian evolution in ecosystems," applied their basic apparatus to
the problem of speciation in individual taxa within ecosystems, primarily to test
whether or not the pattern of punctuational equilibrium would emerge. "We do not
mean," they write (1993, p. 137), "a large multispecies extinction event but rather
the sudden disappearance of an evolutionary stable state causing a species to
undergo very rapid evolution to a different state."
Under basic trade-off "rules" of bioenergetics and ecological interaction,
which they call "constraints" (correlations, for example, between a prey's increase
in population size and the exposure of individuals to a predator's attention),
punctuated equilibrium emerges as a general pattern. Gradual change may prevail
in systems without such constraints, but as the authors state, and to say the very
least about nature's evident complexity!!), "the absence of such constraints is
biologically unrealistic" (1993, p. 138). Moreover, they argue, reasonable features
of the model's internal operation, and recognized properties of natural ecosystems,
suggest a general status for punctuational change at all levels: "In this note," Rand
and Wilson write (1993, p. 137), "we wish to address the important issue of
gradualism against punctualism in evolutionary theory. We discuss this in terms of
a simple illustrative example, but emphasize that... our results apply quite
generally and are ubiquitous and wide ranging."
Explicit modelling of other levels has also yielded punctuational change as an
expectation and generality under realistic assumptions. Elsewhere, I discuss
models for punctuational anagenesis within populations in ecological time (see p.
877), erroneously interpreted by some critics as a demonstration that punctuated
equilibrium emerges from ordinary microevolutionary dynamics and therefore
embodies nothing original—although such studies should be interpreted as
illustrating the potential generality of punctuational change by rendering the same
pattern as an anticipated result of different