752 THE STRUCTURE OF EVOLUTIONARY THEORY
This peculiar situation of discordance between the knowledge of practical
experts and the expectation of theorists impressed Eldredge and me deeply when
we formulated punctuated equilibrium. We therefore made the following remarks
in closing our first paper on the application of our model to biostratigraphy
(Eldredge and Gould, 1977):
[We] wondered why evolutionary paleontologists have continued to seek,
for over a century and almost always in vain, the "insensibly graded series"
that Darwin told us to find. Biostratigraphers have known for years that
morphological stability, particularly in characters that allow us to recognize
species-level taxa, is the rule, not the exception. It is time for evolutionary
theory to catch up with empirical paleontology, to confront the
phenomenon of evolutionary non-change, and to incorporate it into our
theory, rather than simply explain it away ... We believe that,
unconsciously, biostratigraphic methodology has been evolutionarily based
all along, since biostratigraphers have always treated their data as if species
do not change much during their [residence in any local section], are
tolerably distinguishable from their nearest relatives, and do not grade
insensibly into their close relatives in adjacent stratigraphic horizons ...
Biostratigraphers, thankfully, have ignored theories of speciation, since the
only one traditionally available to them has not made much sense. To date,
evolutionary theory owes more to biostratigraphy than vice versa. Perhaps
in the future evolutionary theory can begin to repay its debt.Finally, the witness of experts engaged in a lifelong study of particular groups
and times provides especially persuasive testimony because, as I have emphasized
throughout this book, natural history is a science of relative frequencies, not of
unique cases, however well documented. We* have never doubted that examples
of both gradualism and punctuation can be found in the history of almost any
group. The debate about punctuated equilibrium rests upon our claim for a
dominant relative frequency, not for mere occurrence. The summed experiences of
long and distinguished careers therefore provide a good basis for proper
assessment.
The paleontological literature, particularly in the "summing up" articles of
dedicated specialists, abounds in testimony for predominant stasis, often viewed as
surprising, anomalous, or even a bit embarrassing, because such experts had been
trained to expect gradualism, particularly as the reward of diligent study. To
choose some examples in just three prominent fossil groups representing the full
span of conventional "complexity" in the invertebrate record, most microorganisms
seem to show predominant stasis—despite the excellent documentation of a few
"best cases" of gradualism in Cenozoic planktonic Foraminifera (see pp. 803-
810). For example, MacGillavry
*I may be an arrogant man, but I would never be so pompous as to use the 'royal'
we. I cannot separate my views on punctuated equilibrium from those of my colleague
and partner in this venture from the start, Niles Eldredge. When I write 'we' in this
section, I mean 'Eldredge and Gould.'