The Structure of Evolutionary Theory

by Stephen Jay Gould

  Let me therefore end this chapter by restating the last paragraph of the re­view article for Nature that Eldredge and I wrote (Gould and Eldredge, 1993, p. 227) to celebrate the true majority, or coming of age — that is, the 21st birthday — of punctuated equilibrium. We wrote this paragraph to assess the role of punctuated equilibrium within a larger and far more general intellec­tual (and cultural) movement that, obviously, punctuated equilibrium did not create or even instigate, but that our theory didn't simply or slavishly follow either. We did, I think, contribute some terms and concepts to the larger enterprise, [Page 972] and we did encourage scholars in distant fields to apply a mode of thinking, and a model of change, that had formerly been as unconventional (or even denigrated) in their fields as in ours. But we do find ourselves in the paradoxical, and at least mildly uncomfortable, position — as we tried to ex­press in these closing words of our earlier article — of having developed a the­ory with empirical power, and at least some theoretical interest, in its own evolutionary realm, but that must largely depend, for any ultimate historical assessment, upon the fate and efficacy of more general intellectual currents (including both dangerous winds of fashion and solid strata of documenta­tion) well beyond our control of competence.

  In summarizing the impact of recent theories upon human concepts of nature's order, we cannot yet know whether we have witnessed a mighty gain in insight about the natural world (against anthropocentric hopes and biases that always hold us down), or just another transient blip in the history of correspondence between misperceptions of nature and pre­vailing social realities of war and uncertainty. Nonetheless, contempo­rary science has massively substituted notions of indeterminacy, histori­cal contingency, chaos and punctuation for previous convictions about gradual, progressive, predictable determinism. These transitions have occurred in field after field. Punctuated equilibrium, in this light, is only paleontology's contribution to a Zeitgeist, and Zeitgeists, as (literally) transient ghosts of time, should never be trusted. Thus, in developing punctuated equilibrium, we have either been toadies and panderers to fashion, or therefore destined for history's ashheap, or we had a spark of insight about nature's constitution. Only the punctuational and un­predictable future can tell.

  Appendix: A Largely Sociological (and Fully Partisan)

  History of the Impact and Critique of Punctuated

  Equilibrium

  THE ENTRANCE OF PUNCTUATED EQUILIBRIUM INTO COMMON LANGUAGE AND GENERAL CULTURE

  As a personal indulgence, after nearly 20 years' work on this book, I wish to present an unabashedly subjective, but in no sense either consciously inaccu­rate or even incomplete, account of the extra-scientific impact and criticism of punctuated equilibrium during its first quarter century. As extra-scientific, I include both the spread and influence of punctuated equilibrium into non-biological fields and into general culture, and also the subset of opinions voiced by biological colleagues, that, in my judgment, are not based on logi­cal or empirical argument, but rather on personal feelings spanning the gamut from appreciation to bitter jealousy and anger. I realize that such an ef­fort, which I do regard as self-indulgent, may be viewed as unseemly by some colleagues. I would only reply, first — speaking personally — that I have, perhaps, [Page 973] earned the right after so much deprecation (matched or exceeded, to be sure, by a great deal of support); and second — speaking generally — that such an effort may have value for people interested in metacommentary upon sci­ence (historians, sociologists, scientific colleagues with an introspective bent), if only because few scientific theories garner so wide a spate of reactions, both popular and professional (and for reasons both worthy and lamentable). Moreover, the comments, while necessarily and admittedly partisan, of an originator of the theory (who has also kept a chronological file, as complete as he could manage, on the developing discussion) might have some worth as primary source material (in contrast with more objective, but second­ary, analysis and interpretation). Therefore, I do not, in this section, include any overt discussion of the rich and numerous scientific critiques, issues, ex­tensions, and arguments inspired by punctuated equilibrium. These subjects have already been treated in the main body of this chapter.

  Needless to say, density and intensity of discussion bear no necessary correlation with the worth or validity of a subject; after all, many theological phenomena that have provoked wars, filled libraries, and consumed the lives of countless scholars, may not exist at all. Still, if only for naive reasons, I take a generally hopeful view about human intelligence and discernment — at least to the extent of believing that when large numbers of thoughtful people choose to devote substantial segments of careers to the consideration of a new idea, this expenditure probably records the idea's genuine value and in­terest, and does not represent a pure snare or delusion.

  Thus, above all else, I take pleasure in the perceived and expressed utility of punctuated equilibrium in altering a field that had largely languished in dol­drums of little to do (as gradualism had defined the domain of recognized empirics for fine-scale evolution, and very few cases of paleontological gradu­alism could ever be documented) — and in providing an operational base for fruitful study by showing that the primary empirical signals of stasis and punctuation represented meaningful data on the tempo and mode of evolu­tion, and not just a mocking signal from nature about the discouraging im­perfection of the fossil record. The greatest success of punctuated equilibrium lies not in any torrent of words provoked by the theory, but in the volume of empirical study pursued under its aegis by paleontologists throughout the world (see Section IV of this chapter, for an account of this literature).

  While this professional debate unfolded in full force, the name and concept of punctuated equilibrium also moved from the scientific literature into gen­eral culture, at least on the intellectual edges, but often into more popular consciousness as well. Consider five categories recording this spread:

  1. ESTABLISHMENT OF THE NAME IN DICTIONARIES AND LITERATURE. Punctuated equilibrium has won entry to latest editions of standard general dictionaries of the English language, including the Addenda to Webster's Third New International Dictionary (1986), where it shares a page with such other neologisms as psychedelic, psychobabble, pump iron, putz, quark, rab­bit ears (which, as a name for those old indoor TV antennas, will no doubt pass quickly [Page 974] into oblivion along with the item itself), and race walking. I congratulate Webster's on a better and more accurate definition than many pro­fessional colleagues have misdevised for their denigrations. Webster's sug­gests: “a lineage of evolutionary descent characterized by long periods of stability in characteristics of the organism and short periods of rapid change during which new forms appear esp. from small subpopulations of the ances­tral form in restricted parts of its geographic range.” Punctuated equilibrium also occurs in most alphabetical compendia of scientific terms and concepts, including the World Information Systems Almanac of Science and Technol­ogy (Golob and Brus, 1990), The Penguin Dictionary of Biology (Thain and Hickman, 1990), and the Oxford Dictionary of Natural History (Allaby, 1985).

  As a further mark of general recognition, several novelists have made ca­sual references to punctuated equilibrium (in works for mass audiences, not arcana for the literati). Stephen King mentions punctuated equilibrium in chapter 30, “Thayer gets weird,” of The Talisman. The celebrated English novelist John Fowles included the following passage in his novel, A Maggot. (Fowles, a distinguished amateur paleontologist himself, also created fiction's outstanding paleontologist, the hero of his novel, The French Lieutenant's Woman): “This particular last day of April falls in a year very nearly equidis­tant from 1689, the culmination of the English Revolution, and 1789, the start of the French; in a sort of dozing solstitial standstill, a stasis of the kind predicted by those today who see all evolution as a punctuated equilibrium.” In his 1982 crime novel, The Man at the Wheel, Michael Kenyon doesn't cite the name, and does veer towards the common saltatio
nal confusion, but pre­sumably wrote this passage in the light of public discussion about punctuated equilibrium. “Now there're biologists saying Darwin got it wrong, or at any rate not wholly right, because evolution isn't slow, continuous change, it's sudden bursts of change after millions of years of nothing, so if the polar bear happened suddenly, why not the world?”

  2. LISTING THE THEORY AS AN EVENT IN CHRONOLOGICAL ACCOUNTS OF THE GROWTH OF 20TH CENTURY KNOWLEDGE. Isaac Asimov cited punctuated equilibrium among the seven events of world science chosen to characterize 1972 in his book, Asimov's Chronology of Science and Technol­ogy (1989). Rensberger (1986) included punctuated equilibrium in his alpha­betical compendium How the World Works: A Guide to Science's Greatest Discoveries. In Our Times (Glennon, 1995), a lavishly illustrated “coffee ta­ble” book on the cultural history of the 20th century used the Darwinian centennial of 1982 for discussing the strength of evolution (contra creation-ism) and the status of the field. Among three “takes” to mark the year (evolu­tion shared space with acid rain and Madonna's first single recording, while a sidebar list of “new in 1982” includes liposuction and Halcion sleeping pills), the column on evolution bears the title “Darwin refined,” and concentrates exclusively on punctuated equilibrium. In a refreshing departure from com­mon journalistic accounts, the epitome is both incisive and generally accu­rate: “... The theory of punctuated equilibria reconciled Darwinism with [Page 975] paleontological reality ... The debate could be traced back to Darwin, who'd candidly admitted that gradual evolution did not square with the fossil rec­ord. Gould emphasized that Darwinism was 'incomplete, not incorrect.' The theory of punctuated equilibria, however, proved a crucial refinement of Dar­winian thought, as well as a useful model for other disciplines from anthro­pology to political science.”

  In a long article for The New Yorker on the history of the American Mu­seum of Natural History, Traub (1995) emphasized the frustration of staff scientists when public supporters only recognize exhibits and have no inkling that the Museum also operates as a distinguished institute of scientific re­search. In listing accomplishments from Boaz to Mead in anthropology, and from Osborn to Simpson and Mayr for paleontology and evolution, Traub mentioned only punctuated equilibrium to mark the continuation of this tra­dition into recent years: “And in the early seventies, Stephen Jay Gould and Niles Eldredge accounted for anomalies in the fossil record by arguing that evolution proceeded not steadily but sporadically — a theory known as 'punc­tuated equilibria.'”

  I acknowledge, of course, the blatant unfairness of this selectivity, espe­cially the legitimate grievances prompted thereby among those who built cladistic theory at the Museum during these same years. I cite this example (with some mixture of embarrassment and, to be honest, a tinge of pride as well) to point out how punctuated equilibrium became, in popular culture, a synecdoche for professional discussion about evolution. I also recognize that this journalistic ploy rightly angers and inspires jealousy among colleagues; I merely point out that Eldredge and I cannot fairly be blamed for this cultural phenomenon. Neither of us ever organized a symposium, or even called a re­porter, to discuss punctuated equilibrium in public (and neither of us was in­terviewed by the author of this New Yorker article).

  3. international spread. Punctuated equilibrium has been promi­nently discussed in newspaper and magazine articles of nearly all major West­ern nations — in France as equilibres intermittents (Blanc, 1982) or equilibres ponctues (the leading newspaper he Monde of May 26, 1982; Devillers and Chaline, 1989; Courtillot, 1995); in Spain and Latin America as equilibrio interrumpido (Sequieros, 1981) or equilibrio punctuado (Valdecasas and Herreros, 1982; Franco, 1985); in Italy as equilibri punteggiati (Salvatori, 1984); and in Germany as Unterbrochenen Gleichgewichts (Glaubrecht, 1995). (All these citations come from popular articles about the theory, not from biopic pieces about the authors, or from technical literature.)

  Punctuated equilibrium has also been featured in Western but non Indo-European, accounts in Hungary, Finland and Turkey, and in several articles of the non-Western press, notably in India, Japan, Korea and China. The theory even penetrated the strongest of political iron curtains to emerge, on March 21, 1983, as a feature article in Maoist Mainland China's major newspaper Ren Min Ri Bao (The People's Daily). They wrote, in a commentary not nota­ble for accuracy: “Theories against Darwin have taken the opportunity to [Page 976] make their appearances. The most typical of all this is the theory of 'punctu­ated equilibrium' . . . This theory holds that organic evolution proceeds by leaps and bounds and not through continuous change.”

  4. textbooks. This criterion may be viewed as the most unenviable of all, but when a new idea enters textbooks as a “standard,” almost obligatory item (remember that no other written genre ranks as more conservative or more cloned through endless copying and regimentation by publishers' re­quirements), then we may affirm that the notion has flowed into a cultural mainstream. As I shall document on pages 994–999, punctuated equilibrium has become a standard entry in textbooks at both the college and high school levels in America.

  5. An item in general culture. When the National Center for Sci­ence Education, America's leading anti-creationist organization, put out two bumper stickers as sardonic comments upon the favored evangelical “Honk if you love Jesus,” they chose “Honk if you love Darwin” and “Honk if you un­derstand punctuated equilibrium.” (Niles Eldredge tells me that, in his car one day, he became frightened by a persistent honker; when he ventured a sheepish glance, fearing an encounter with a gun, or at least an upraised third finger, he noted only a smile on the other driver's face, and a finger pointing downward to the bumper sticker.) My colleagues may be satirizing punctu­ated equilibrium as terminological mumbo jumbo, but at least they thought they could raise some money (and some laughs) with this item!

  Although not always understood or properly employed (but often, to my surprise and gratification, excellently epitomized and tactfully used), punctu­ated equilibrium has become a recognized term and concept both in scholar­ship of widely disparate fields, and in popular culture. I first noted this spread in 1978, a few years before punctuated equilibrium splashed into public recognition, when nationally syndicated columnist Ellen Goodman featured punctuated equilibrium in an op-ed piece entitled “Crisis is a way of life bringing sudden change.” I feel that Goodman, then unknown to me but now a respected colleague and friend, captured the essence of punctuated equilib­rium's suggestions about the general nature of change, and did so with clarity and insight — a good beginning, not always followed in later commentary. Goodman wrote (in part):

  I am not normally the sort of person who curls up in front of the fire with a good science book. The last time I found Charles Darwin interesting was in “Inherit the Wind.” But I was still intrigued by Stephen Ray [sic] Gould's thoughts about evolution . . . [for he] has written about natural change in a way that makes sense out of our current lives and not just out of fossils. Gould thinks Darwin's view of evolution . . . was actually “a philosophy of change, not an indication from nature.” he says that “gradualism” was part of the 19th century prejudice in favor of orderli­ness ... In that sense, I suppose we are all still Darwinians. How many of us harbor the hope that the change in our lives will be gradual, rather [Page 977] like being promoted from the seventh grade to the eighth. We would like our lives to be an accumulation of skills and wisdom . . .

  [But] people may go through the greatest changes in their lives in the shortest chunks of time. I have known someone who, after years of stagnation, raced through a decade of personal growth in the first year of a new career. I have known others who experienced a generation's worth of change in six post-divorce months. ..

  We often underestimate the suddenness, even the randomness, of the change itself. I suppose that our observations are no more colored than Darwin's. We see gradual change, in part, because we go looking for it. We find it because we need it. Our research into the past reflects
our fear of the future . . . Natural history is, as [Gould] puts it, “a series of pla­teaus punctuated by rare and seminal events that shift systems from one level to another.” In that way, I suspect, people have a lot in common with rocks.

  Punctuated equilibrium has often been the explicit focus of scholarship in distant fields (see pp. 952–967 for a technical discussion with extended exam­ples; I only mention the range of invocations here) — including a lead article by Gans (1987) on “punctuated equilibria and political science” with five commentaries by other scholars and a response by Gans in the journal Poli­tics and the Life Sciences; an analysis of my rhetorical style by Lyne and Howe (1986) in the Quarterly Journal of Speech; and an exchange between Thompson (1983) and Stidd (1985) in the journal Philosophy of Science. However, the general spread of punctuated equilibrium into vernacular cul­ture will not be best illustrated by such explicit treatments (which may be read as didactic efforts to instruct), but rather by more casual comments im­plying a shared context of presumed understanding before the fact. I there­fore present a partial and eclectic list, united only by the chancy criterion that someone called the items to my attention: