The Structure of Evolutionary Theory

by Stephen Jay Gould

  The wages of jealousy

  THE DESCENT TO NASTINESS. I treated the general ad hominem case against punctuated equilibrium in the last section. But some specific charges against punctuated equilibrium have bordered on the inane, or even the po­tentially actionable in our litigious world. To mention a few highlights along this low road:

  The charge of dishonesty. The following event unfolds with la­mentable predictability in our imperfect world: when a controversy becomes impassioned, someone will eventually try to land the lowest academic blow of all by launching a charge of plagiarism or dishonest quotation. The debate about punctuated equilibrium reached this nadir when Penny (1983) accused us of cooking a quote from the Origin of Species by omitting passages with­out noting the deletion, and thereby changing Darwin's meaning to suit our purposes. Penny quoted from the 6th edition of the Origin to back up his claim. We, however, had used the first edition — and had rendered Darwin's words accurately (Gould and Eldredge, 1983). Enough said.

  The charge of rip-off. A more conventional strategy for those who wish to deny a colleague's originality consists in claiming that a putative nov­elty really has an old pedigree — a twice-told tale, said long before, preferably by a leading scientific light, and not in an obscure source (so that those under question cannot claim forgivable ignorance of minutiae). I suppose, there­fore, that when we began to arouse substantial jealousy, someone was bound to argue that Darwin himself had said it all before.

  The litany of this claim may hold some sociological interest for the time and energy invested by several commentators (Penny, 1983,1985; Gingerich, 1984a and b, 1985; Scudo, 1985). These authors did point out some le­gitimate similarities between certain Darwinian statements and the tenets of punctuated equilibrium — including a significant one-sentence addition to later editions of the Origin (which we had indeed missed), acknowledging the occurrence of punctuational tempos, and apparently inspired by Falconer's objections, as highlighted in the introductory section of this chapter.

  I regard this case as fundamentally misguided for general historiographic reasons, outlined in Gould and Eldredge (1983, p. 444):

  One simply cannot do history by searching for footnotes and incidental statements, particularly in later editions that compromise original state­ments. As with the Bible, most anything can be found somewhere in Dar­win. General tenor, not occasional commentary, must be the criterion for judging a scientist's basic conceptions. If Darwin historians agree on a [Page 1015] single point (for example, see Gruber [1974] and Mayr [1982b]), it is the importance and pervasiveness of Darwin's gradualism — a commitment far stronger than his allegiance to natural selection as an evolutionary mechanism.

  Fortunately, one needn't take my partisan word in refutation. Frank Rhodes, then the president of Cornell University, but a distinguished paleon­tologist by training and first career, became interested in punctuated equilib­rium and its links to the history of evolutionary thought. He therefore spent a sabbatical term researching the relationship of Darwin's thinking to the claims and tenets of punctuated equilibrium. He did find many genuine Dar­winian resonances, while affirming our originality and concluding, “the hypothesis of punctuated equilibrium is of major importance for paleontological theory and practice” (Rhodes, 1983, p. 272).

  When Gingerich (1984, p. 116) wrote a commentary on Rhodes's article, dedicated to denying our originality and asserting once again that Darwin had said it all before, Rhodes replied with generosity and firmness (under Gingerich, 1985, p. 116):

  I do argue that punctuated equilibrium — whether true or false — is a “hypothesis of major importance” and that it has had a beneficial impact on the quality of recent paleontological studies. Gingerich asks, “Which nu­ances [of punctuated equilibrium] were unanticipated by Darwin?” From a long list, I suggest the following: its relationship to the genetics of stasis and the punctuation, morphological stasis and developmental con­straints, evolutionary models in relation to paleoecology, stratigraphical correlation, species selection, mathematical models of evolutionary rates, selection of RNA molecules, phylogenetic divergence, and the evo­lution of communities. These topics, and many more studied from the viewpoint of punctuated equilibrium, have been the subject of recent pa­pers ... To suggest that there was no nuance of punctuated equilibrium which was “unanticipated by Darwin” is to make an icon of Darwin and to adopt an extravagantly Whiggish view of the history of Darwin's par­ticular contribution — great as that was.

  Some critics then followed a substitutional strategy: if one denigration fails, try another in the same form. If “Darwin said it all” fails as an optimal dismissal, then try the best available paleontological version: “G. G. Simpson said it all.” Again, the search for reinterpretations and footnotes began, as this new version of denigration began to coagulate among our most commit­ted detractors: Simpson (1944) devoted his seminal book to documenting the great variation in evolutionary rates, and punctuated equilibrium therefore has nothing new to say.

  But, punctuated equilibrium was never formulated as a hypothesis about great variability in anagenetic rates (which, indeed, everyone has long ac­knowledged). Punctuated equilibrium presents a specific hypothesis about the location of most evolutionary change in punctuational cladogenesis, followed [Page 1016] by pronounced stasis. Yet Simpson, as documented in Chapter 7, pages 562–563, denied major importance to cladogenesis at all, and held that 90 percent of evolutionary change occurred in the anagenetic mode. Moreover (see pages 528–531), Simpson's important hypothesis of “quantum evolution” — the idea that our detractors usually try to depict as equivalent to punctuated equilibrium — treats a vitally important, but entirely different phenomenon of different mode at a different scale: the anagenetic origin of major structural innovations, not the pacing of ordinary speciation.

  Several authors, in their desire to name Simpson as the true author of punc­tuated equilibrium, completely misunderstood his work. Andrew Huxley, for example, misinterpreted the well-known paleontological concept of a Stufenreihe. Huxley quoted from Simpson's 1944 book (Huxley, 1982, p. 145): “He says (pp. 194-195): 'The pattern of step-like evolution, an ap­pearance of successive structural steps, rather than direct sequential phyletic transitions, is a peculiarity of paleontological data more nearly universal than true rectilinearity and often mistaken for the latter,' and quotes the name Stufenreihe given to this mode of evolution by Abel in 1929. This is exactly equivalent to 'punctuated equilibria.'” But a Stufenreihe is a stratigraphic se­quence displaying an evolutionary trend constructed of collateral relatives rather than direct ancestors (called, by contrast, an Ahnenreihe). For exam­ple, Australopithecus robustus, Homo neanderthalensis and Homo sapiens form a Stufenreihe, while A. afarensis, Homo ergaster, and Homo sapiens build a putative Ahnenreihe. Stufenreihen are necessarily discontinuous be­cause they pile a cousin on top of an uncle on top of a grandfather, while true Ahnenreihen record genuine genealogical descent without breaks. In any case, the contrast bears no relationship to the concept of punctuated equilib­rium (which is a hypothesis about the geometry of Ahnenreihen).

  Mettler, Gregg and Schaffer (1988, p. 288) even grant Simpson authorship of our name! “Finally, there is the punctuated equilibrium view of Eldredge and Gould (1972), and Vrba (1983). Even though the term was coined by Simpson, these authors have given it new emphasis.”

  At least pathos can be balanced by bathos in our wondrously varied world. The irrepressible Beverly Halstead, labelling me with my all-time favorite epi­thet of “petty obnoxious in fauna,” while depicting Simpson as a deity watch­ing over his loyal epigones from on high, reviewed Simpson's last book with a panegyric that left even his earlier excoriation of the British Museum in the rhetorical dust (Halstead, 1984, p. 40):

  Indeed, the original presentation of punctuated equilibrium was in anti-neo-Darwinian language but the substance was nonetheless easily ac­commodated within the framework given long ago by Simpson ... It has been Simpson'
s overwhelming reasonableness and commonsense, as ex­emplified in this book, that has done so much to entrench the Modern Synthesis in the consciousness of most paleontologists, the literary pyro­technics of Steve Gould notwithstanding. Simpson's humility before his [Page 1017] fossils, a special kind of innocence, is perhaps one of his most endearing traits. Because he is kind and tolerant, he finds it nigh impossible to be­lieve that some of the supporting framework of our discipline is infested with some petty obnoxious infauna. My only criticism of Simpson in his book is his apparent unwillingness to contemplate the existence of real nasties emerging from the woodwork . . . Let him [Simpson] look down from the commanding heights knowing that the citadel of neo-Darwin-ism still has its staunch defenders in this more combative age. We will do our best not to let him down.

  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 [Page 1018] 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 [Page 1019] 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 unsealed, 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 punctuat
ed 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.” [Page 1020]

  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).