Punctuated Equilibrium and the Validation of Macroevolutionary Theory 775
and Eldredge and I do take pride in the role played by punctuated equilibrium in
encouraging this shift of interest—as a profession of paleobiology, supported by
several new journals dedicated to the subject (Paleobiology, Historical Biology,
Lethaea, Palaios, and Palaeogeography Palaeoclimatology Palaeoecology (or P-
cubed to aficionados), for example), has arisen to accommodate burgeoning
research in the application of evolutionary theory to the fossil record, and in
enlarging and revising the theory in the light of novel macroevolutionary data.
In any case, Schopf's symposium featured a series of presentations; each
suggesting how one aspect of paleontological work might be enlightened by
modern microevolutionary theory, particularly as expressed in the application of
models, preferably quantitative in nature. Eldredge and I drew the topic of species
and speciation—and our original article on punctuated equilibrium (Eldredge and
Gould, 1972) emerged as a result. (As I have often stated, the basic idea had been
presented in Eldredge, 1971. We had been graduate students together at the
American Museum of Natural History, under the tutelage of Norman D. Newell.
We had discussed these issues often and intensely throughout our graduate years.
We had been particularly frustrated—for we had both struggled to master statistical
and other quantitative methods—with the difficulty of locating gradualistic
sequences for applying these techniques, and therefore for documenting
"evolution" as paleontological tradition then defined the term and activity. When I
received Schopf's invitation to talk on models of speciation, I felt that Eldredge's
1971 publication had presented the only new and interesting ideas on
paleontological implications of the subject—so I asked Schopf if we could present
the paper jointly. I wrote most of our 1972 paper, and I did coin the term
punctuated equilibrium—but the basic structure of the theory belongs to Eldredge,
with priority established in his 1971 paper.)
I mention this background to clarify the original context and continuing focus
of the theory of punctuated equilibrium—a notion rooted in the explicit goal that
Eldredge and I set for ourselves: to apply microevolutionary ideas about speciation
to the data of the fossil record and the scale of geological time. Before we
proposed the theory of punctuated equilibrium, most paleontologists assumed that
the bulk of evolutionary change proceeded in the anagenetic mode—that is, by
continuous transformation of a unitary population through time (see Fig. 9-5). In
this context, most paleontological discussion about species centered itself upon a
contentious issue that constantly circulated throughout our literature (see Imbrie,
1957; Weller, 1961; McAlester, 1962; Shaw, 1969) and even generated entire
symposia dedicated to potential solutions (see Sylvester-Bradley, 1956): the so-
called species problem in paleontology.
This supposed problem—more philosophical and definitional than empirical
(once one accepts the underlying assumptions about anagenesis as a dominant
factual reality)—arises because a true continuum cannot be unambiguously divided
into segments with discrete names. If population A changes so extensively by
anagenesis that we feel impelled to provide the resulting population