Punctuated Equilibrium's Threefold History
by Stephen Jay Gould
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"Urban Legend" of Punctuated Equilibrium's Threefold History: The opponents
of punctuated equilibrium have constructed a fictional history of the theory,
primarily (I suppose) as a largely unconscious expression of their hope for its
minor importance […] This supposed threefold history of punctuated
equilibrium also ranks about as close to pure fiction as any recent commentary by
scientists has ever generated. In stage one, the story goes, we were properly
modest, obedient to the theoretical hegemony of the Modern Synthesis, and merely
trying to bring paleontology into the fold. But the prospect of worldly fame
beguiled us, so we broke our ties of fealty and tried, in stage two, to usurp
power by painting punctuated equilibrium as a revolutionary doctrine that would
dethrone the Synthesis, resurrect the memory of the exiled martyr (Richard
Goldschmidt), and reign over a reconstructed realm of theory. But we were too
big for our breeches, and the old guard still retained some life. They fought
back mightily and effectively, exposing our bombast and emptiness. We began to
hedge, retreat, and apologize, and have been doing so ever since in an effort to
regain grace and, chastened in stage three, to sit again, in heaven or Valhalla,
with the evolutionary elite.
Such farfetched fiction suffers most of all from an internal
construction that precludes exposure and falsification among true believers,
whatever the evidence. Purveyors of this myth even name the three stages, thus
solidifying the false taxonomy. Dawkins (1986), for example, speaks of the
"grandiloquent era…of middle-period punctuationism [which] gave abundant aid
and comfort to creationists and other enemies of scientific truth." In the other
major strategy of insulation from refutation, supporters of this "urban legend"
about the modest origin, bombastic rise, and spectacular fall of punctuated
equilibrium forge a tale that allows them to read any potential disconfirmation as
an event within the fiction itself. […]
In particular, and most offensive to me, the urban legend rests
on the false belief that radical, "middle-period" punctuated equilibrium became a
saltational theory wedded to Goldschmidt's hopeful monsters as a mechanism. I have
labored to refute this nonsensical charge from the day I first heard it. But my
efforts are doomed within the self-affirming structure of the urban legend. We all
know, for so the legend proclaims, that I once took the Goldschmidtian plunge. So
if I ever deny the link, I can only be retreating from an embarrassing error. And
if I, continue to deny the link with force and gusto, well, then I am only
backtracking even harder (into stage 3) and apologizing (or obfuscating) all the
more. How about the obvious (and accurate) alternative: that we never made the
Goldschmidtian link; that this common error embodies a false construction; and that
our efforts at correction have always represented an honorable attempt to relieve
the confusion of others.
But the urban legend remains too simplistically neat, and too
resonant with a favorite theme of Western sagas, to permit refutation by mere
evidence. So Dennett (1995, pp. 283-284) writes: "There was no mention in the first
paper of any radical theory of speciation or mutation. But later, about 1980,
Gould decided that punctuated equilibrium was a revolutionary idea after all
[But] it was too revolutionary, and it was hooted down with the same sort of
ferocity the establishment reserves for heretics like Elaine Morgan. Gould
backpedaled hard, offering repeated denials that he has ever meant anything so
outrageous." And Halstead (1985, p. 318) wrote of me (with equal poverty in both
logic and grammar): "He seems to be setting up a face-saving formula to enable
him to retreat from his earlier aggressive saltationism, having had a bit of a
thrashing, his current tack is to suggest that perhaps we should keep the door
open in case he can find some evidence to support his pet theories so let us be
'pluralist.'"
I do not, of course, claim that our views about punctuated
equilibrium have never changed through the years of debate (only a dull and
uninteresting theory could remain so static in the face of such wide discussion).
Nor do I maintain a position that would be even sillier—namely, that we made
no important errors requiring corrections to the theory. Of course we made
mistakes, and of course we have tried to amend them. But I look upon the history
of punctuated equilibrium (from my partisan vantage point of course) as a fairly
standard development for successful theories in science. We did, indeed, begin
modestly and expand outward thereafter. (In this sense, punctuated equilibrium
has grown in theoretical scope, primarily as macroevolutionary theory developed
and became better integrated with the rest of evolutionary thought—and
largely through articulation of the hierarchical model, as discussed in the
previous chapter).
We started small as a consequence of our ignorance and lack of
perspective, not from modesty of basic temperament. As stated before, we simply
didn't recognize, at first, the interesting implications of punctuated equilibrium
for macroevolutionary theory—primarily gained in treating species as
Darwinian individuals for the explanation of trends, and in exploring the extent
and causes of stasis. With the help of S. M. Stanley, E. S. Vrba and other
colleagues, we developed these implications over the years, and the theory grew
accordingly. But we never proposed a radical theory for punctuations (ordinary
speciation scaled into geological time), and we never linked punctuations to
microevolutionary saltationism.
Of course we made mistakes—serious ones in at least two
cases—and the theory has changed and improved by correcting these errors.
In particular, and as documented extensively in Chapter 8, we were terribly
muddled for several years about the proper way to treat, and even to define,
selection at the level of species—the most important of all theoretical
spinoffs from punctuated equilibrium. We confused sorting with selection (see Vrba
and Gould, 1986, for a resolution). We also did not properly formulate the concept
of emergence at first; and we remained confused for a long time about emergence of
characters vs. emergence of fitness as criteria for species selection (Lloyd and
Gould, 1993; Gould and Lloyd, 1999). In retrospect, I am chagrined by the long
duration of our confusion, and its expression in many of our papers. But I think
that we have now resolved these difficult issues. […]
The saltationist canard has persisted as our incubus. The
charge could never be supported by proper documentation, for we never made the
link or claim. All attempts collapse upon close examination. Dennett, for
example, who insists (1997, p. 64) that "for a while he [Gould] had presented
punctuated equilibrium as a revolutionary 'saitationist' alternative to standard
neo-Darwinism," documents his supposed best case by assuring readers (1995, p.
285) that "for a while, Gould was proposing that the first step in the
establishment of any new species was a doozy—a non-Darwinian saltation."
Dennett directly follows this claim with his putative proof, yet another
quotation from my 1980 paper, which he renders As follows: "Speciation is not
always an extension of gradual, adaptive allelic substitution to greater effect,
but may represent, as Goldschmidt argued, a different style of genetic
change—rapid reorganization of the genome, perhaps non-adaptive" (Gould,
1980b, p. 119).
I regard Dennett's case as pitiful, but the urban legend can
offer no better. First of all, this quotation doesn't even refer to punctuated
equilibrium, but comes from a section of my 1980 paper on the microevolutionary
mechanics of speciation. Secondly, Dennett obviously misreads my statement in a
backwards manner. I am trying to carve out a small theoretical space for
a style of microevolutionary rapidity at low relative frequency—as clearly
stated in my phrase "not always an extension of gradual…" But Dennett
states that I am proposing this mechanism as a general replacement for gradual
microevolutionary change in all cases of speciation—"the first step
in the establishment of any new species" in his words. But
my chosen phrase—"not always"—clearly means "most of the time,"
and cannot be read as "never." In short, I made a plea for pluralism, and
Dennett charges me with usurpation. Then, when I try to explain, I am accused of
beating a retreat to save face. When placed in such a double bind, one can only
smile and remember Schiller's famous dictum: Mit Dummheit
kimpfen die Gdtter selbst vergebens.
Finally, the claim that we equated punctuated equilibrium
with saltation makes no sense within the logical structure of our theory—so,
unless we are fools, how could we ever have asserted such a proposition? Our
theory holds, as a defining statement, that ordinary allopatric speciation,
unfolding gradually at microevolutionary scales, translates to punctuation in
geological time. Microevolutionary saltation also scales as a punctuation—so
the distinction between saltation and standard allopatry becomes irrelevant for
punctuated equilibrium, since both yield the same favored result!
Moreover, the chronology of debate proves that we did not
issue disclaimers on this subject only to cover our asses as we retreated from
exaggerations of our supposed second phase, because we have been asserting this
clarification from the very beginning—that is, from the first paper we ever
wrote to comment upon published reactions to punctuated equilibrium. Our first
response appeared in 1977, long before we issued the supposed clarion call of
our false revolution in 1980. We wrote (Gould and Eldredge, 1977, p. 121), under
the heading "Invalid claims of gradualism made at the wrong scale": "The model
of punctuated equilibria does not maintain that nothing occurs gradually at any
level of evolution. It is a theory about speciation and its deployment in the
fossil record. It claims that an important pattern, continuous at higher
levels—the 'classic' macroevolutionary trend—is a consequence of
punctuation in the evolution of species. It does not deny that allopatric
speciation occurs gradually in ecological time (though it might not—see
Carson, 1975), but only asserts that this scale is a geological microsecond."
We have never changed this conviction, and we have always tried
to correct any confusion of scaling between saltation and punctuation, even in
papers written during the supposed apogee of our revolutionary ardor, during
illusory stage 2 of the urban legend. For example, under the heading of "The
relationship of punctuated equilibrium to macromutation," I wrote in 1982c (p. 88):
"Punctuated equilibrium is not a theory of macromutation…it is not a theory
of any genetic process…It is a theory about larger-scale patterns-the geometry
of speciation in geological time. As with ecologically rapid modes of speciation,
punctuated equilibrium welcomes macromutation as a source for the initiation of
species: the faster the better. But punctuated equilibrium clearly does not
require or imply macromutation, since it was formulated as the expected
geological consequence of Mayrian allopatry." […]
The Charge of Ulterior Motivation
When charges of dishonesty or lack of originality fail, a
committed detractor can still label his opponents as unconcerned with scientific
truth, but motivated by some ulterior (and nefarious) goal. Speculations about our
"real" reasons have varied widely in content, but little in their shared mean spirit
(see, for example, Turner, 1984; Konner, 1986; and Dennett, 1995). I will discuss
only one of these peculiar speculations—the charge that punctuated equilibrium
originated from my political commitments rather than from any honorable feeling
about the empirical world—because, once again, the claim rests upon a canonical
misquotation and exposes the apparent unwillingness or inability of our unscientific
critics to read a clear text with care.
I have already discussed Halstead's version of the political
charge in the great and farcical British-Museum-cum-cladism-cum-Marxism debate (see
pages 984-985). The supposed justification for this construction lies in another
quotation from my writing, second in false invocation only to the "death of the
Synthesis" statement discussed earlier (p. 1003).
I do not see how any careful reader could have missed the
narrowly focused intent of the last section in our 1977 paper, a discussion of the
central and unexceptionable principle, embraced by all professional historians of
science, that theories must reflect a surrounding social and cultural context. We
began the section by trying to identify the cultural roots of gradualism in larger
beliefs of Victorian society. We wrote (Gould and Eldredge, 1977, p. 145): "The
general preference that so many of us hold for gradualism is a metaphysical stance
embedded in the modern history of Western cultures: it is not a high-order
empirical observation, induced from the objective study of nature . . . We mention
this not to discredit Darwin in any way, but merely to point out that even the
greatest scientific achievements are rooted in their cultural contexts—and to
argue that gradualism was part of the cultural context, not of nature."
We couldn't then assert, with any pretense to fairness or
openness to self-scrutiny, that gradualism represents cultural context, while our
punctuational preferences only record unvarnished empirical truth. If all general
theories embody a complex mixture of contingent context with factual adequacy, then
we had to consider the cultural embeddedness of preferences for punctuational
change as well. We therefore began by writing (p. 145) that "alternative conceptions
of change have respectable pedigrees in philosophy." We then discussed the most
obvious candidate in the history of Western thought: the Hegelian dialectic and its
redefinition by Marx and Engels as a theory of revolutionary social change in human
history. We cited a silly, propagandistic defense of punctuational change from the
official Soviet handbook of Marxism-Leninism, in order to stress our point about
the potential political employment of all general theories of change. We concluded
(p. 146): "It is easy to see the explicit ideology lurking behind this general
statement about the nature of change. May we not also discern the implicit ideology
in our Western preference for gradualism?"
But the argument required one further step for full disclosure.
We needed to say something about why we, rather than other paleontologists at other
times, had developed the concept of punctuated equilibrium. We raised this point
as sociological commentary about the origin of ideas, not as a scientific
argument for the validity of the same ideas. An identification of cultural
or ontogenetic sources says nothing about truth value, an issue that can only be
settled by standard scientific procedures of observation, experiment and empirical
test. So I mentioned a personal factor that probably predisposed me to openness
towards, or at least an explicit awareness of, a punctuational alternative to
conventional gradualistic models of change: "It may also not be irrelevant to our
personal preferences that one of us learned his Marxism, literally at his daddy's
knee."
I have often seen this statement quoted, always completely out
of context, as supposed proof that I advanced punctuated equilibrium in order to
foster a personal political agenda. I resent this absurd misreading. I spoke only
about a fact of my intellectual ontogeny; I said nothing about my political beliefs
(very different from my father's, by the way, and a private matter that I do not
choose to discuss in this forum). I included this line within a discussion of
personal and cultural reasons that might predispose certain scientists towards
consideration of punctuational models—just as I had identified similar
contexts behind more conventional preferences for gradualism. In the next
paragraph, I stated my own personal conclusions about the general validity of
punctuational change-but critics never quote these words, and only cite my father's
postcranial anatomy out of context instead.
We emphatically do not assert the "truth" of this
alternate metaphysic of punctuational change. Any attempt to support the exclusive
validity of such a monistic, a priori, grandiose notion would verge on the
nonsensical. We believe that gradual change characterizes some hierarchical levels,
even though we may attribute it to punctuation at a lower level—the
macroevolutionary trend produced by species selection, for example. We make a
simple plea for pluralism in guiding philosophies—and for the basic
recognition that such philosophies, however hidden and inarticulated, do constrain
all our thought. Nonetheless, we do believe that the punctuational metaphysic may
prove to map tempos of change in our world better and more often than any of its
competitors—if only because systems in steady state are not only common but
also so highly resistant to change.
The Most Unkindest Cut of All
If none of the foregoing charges can bear scrutiny, strategists
of personal denigration still hold an old and conventional tactic in reserve: they
can proclaim a despised theory both trivial and devoid of content. This charge is so
distasteful to any intellectual that one might wonder why detractors don't try such
a tactic more often, and right up front at the outset. But I think we can identify
a solution—the "triviality caper" tends to backfire and to hoist a critic with
his own petard—for if the idea you hate is so trivial, then why bother to
refute it with such intensity? Leave the idea strictly alone and it will surely go
away all by itself. Why fulminate against tongue piercing, goldfish swallowing,
skateboarding, or any other transient fad with no possible staying power?
Nonetheless, perhaps from, desperation, or from severe
frustration that something regarded as personally odious doesn't seem to be fading
away, this charge of triviality has been advanced against punctuated equilibrium,
apparently to small effect. To cite a classic example of backfiring, Gingerich
(1984a, 1984b) tried to dismiss punctuated equilibrium as meaningless and untestable
by definition—and to validate gradualism a priori as "commitment to
empiricism and dedication to the principal [sic] of testability in science" (1984a,
p. 338), with stasis redefined, oxymoronically in my judgment, as "gradualism at
zero rate" (1984a, p. 338). Gingerich then concludes (1984b, p. 116): "Punctuated
equilibrium is unscaled, and by nature untestable. It hardly deserves recognition
as a conjecture of 'major importance for paleontological theory and practice.'
. . . Hypotheses that cannot be tested are of little value in science."
But how can Gingerich square this attempted dismissal with his
own dedication of a decade in his career to testing punctuated equilibrium by
fine-scale quantitative analysis of Tertiary mammals from the western United States
(Gingerich, 1974, 1976)? These studies, which advanced a strong claim for
gradualism, represent the most important empirical research published in the early
phase of the punctuated equilibrium debate. Gingerich then recognized punctuated
equilibrium as an interesting and testable hypothesis, for he spent enormous time
and effort testing and rejecting our ideas for particular mammalian phylogenies.
He then argued explicitly (1978, p. 454): "Their [Eldredge and Gould's] view of
speciation differs considerably from the traditional paleontological view of
dynamic species with gradual evolutionary transitions, but it can be tested by
study of the fossil record."
Among Darwinian fundamentalists (see my
terminology in Gould, 1997d),
charges of triviality have been advanced most prominently and insistently by
Dawkins (1986, p. 251) who evaluates punctuated equilibrium metaphorically as "an
interesting but minor wrinkle on the surface of neo-Darwinian theory"; and by
Dennett (1995, p. 290) who calls punctuated equilibrium "a false-alarm revolution
that was largely if not entirely in the eyes of the beholders."
But a close analysis of Dawkins's and Dennett's arguments
exposes the parochiality of their judgment. They regard punctuated equilibrium as
trivial because our theory doesn't speak to the restricted subset of evolutionary
questions that, for them, defines an exclusive domain of interest for the entire
subject. These men virtually equate evolution with the origin of intricately
adaptive organic design—"organized adaptive complexity," or O.A.C. in
Dawkins's terminology. They then dismiss punctuated equilibrium on the narrow
criterion: "if it doesn't explain the focus of my interests, then it must be
trivial." Dawkins (1984, p. 684), for example, properly notes the implications
of punctuated equilibrium for validation of higher-level selection, but then
writes: "Species-level selection can't explain the evolution of adaptations:
eyes, ears, knee joints, spider webs, behavior patterns, everything, in short,
that many of us want a theory of evolution to explain. Species selection may
happen, but it doesn't seem to do anything much." "Everything"? Does nothing
else but adaptive organismal design excite Dawkins's fancy in the entire and
maximally various realm of evolutionary biology and the history of life—the
"endless forms most beautiful and most wonderful" of Darwin's closing words
(1859, p. 490).
But the truly curious aspect of both Dawkins's and Dennett's
charge lies in their subsequent recognition, and fair discussion, of the
important theoretical implication of punctuated equilibrium—the
establishment of species as Darwinian individuals, and the consequent validation
of species
sorting and selection as a prominent process in a hierarchical theory of
Darwinian evolution. In 1984, Dawkins acknowledged that this aspect of punctuated
equilibrium "does, in a sense, move outside the neo-Darwinian synthesis, narrowly
interpreted. This is about whether a form of natural selection operates at the
level of entire lineages, as well as at the level of individual reproduction
stressed by Darwin and neo-Darwinism."
In his 1986 book, Dawkins then
devotes a substantial part of the chapter following his rejection of punctuated
equilibrium to an evaluation of species selection. But he finishes his exploration
by reimmersion in the same parochial trap of denying importance because the
phenomenon doesn't explain his exclusive interest in adaptive organismal design:
"To conclude the discussion of species selection, it could account for the
pattern of species existing in the world at any particular time. It follows that
it could also account for changing patterns of species as geological ages give
way to later ages, that is, for changing patterns in the fossil record. But it
is not a significant force in the evolution of the complex machinery of life . .
. As I have put it before, species selection may occur but it doesn't seem to do
anything much!" (Dawkins, 1986, pp. 268-269). But doesn't "the pattern of species
existing in the world at any particular time" and "changing patterns in the fossil
record" represent something of evolutionary importance?
At the end of his long riff against punctuated equilibrium,
Dennett also pauses for breath and catches a glimmer of the concept that seems
important and theoretically intriguing to many students of macroevolution
(Dennett, 1995, pp. 297-298):
The right level at which to look for evolutionary
trends, he [Gould] could then claim [indeed I do], is not the level of the gene,
or the organism, but the whole species or clade. Instead of looking at the loss
of particular genes from gene pools, or the differential death of particular
genotypes within a population, look at the differential extinction rate of whole
species and the differential "birth" rate of species—the rate at which a
lineage can speciate into daughter species. This is an interesting idea . . . It
may be true that the best way of seeing the long-term macro-evolutionary pattern
is to look for differences in "lineage fecundity" instead of looking at the
transformations in the individual lineages. This is a powerful proposal worth
taking seriously.
I am puzzled by the discordance and inconsistency, but
gratified by the outcome. Dawkins and Dennett, smart men both, seem unable to
look past the parochial boundaries of their personal interest in evolution, or
their feelings of jealousy towards whatever effectiveness my public questioning
of their sacred cow of Darwinian fundamentalism may have enjoyed (see Gould, 1997d)—so
they must brand punctuated equilibrium as trivial. But they cannot deny the logic
of Darwinian argument, and they do manage to work their way to the genuine
theoretical interest of punctuated equilibrium's major implication, the source of
our primary excitement about the idea from the start.
[ Stephen Jay Gould,
The Structure of
Evolutionary Theory, Cambridge, Massachusetts: Harvard University Press,
2002, pp. 1006-1021. ]
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