* Well, that took longer than anticipated. But anyway, here is the third part of my three-part essay on Stephen Jay Gould and punctuated equilibria (PE). To read Part 1 and Part 2, follow the links. “Problematica” is written by Max Dresow…
For fans of intellectual history, few phenomena hold more fascination than the proverbial about-face. Think of Sydney Hook, the prominent Marxist philosopher who became one of America’s most zealous (and ridiculous) anti-communists. Or St. George Mivart, Darwin’s critic and a Roman Catholic, who ended his life pouring venom on the throne of Saint Peter. There is high drama in these metamorphoses, especially when the transformation seems to touch the very soul. And so they fascinate us. We simply can’t imagine how this person could have said that, and with all the conviction that once fed the fires of a contrary passion.
This essay examines one such transformation. It asks how an adaptationist with a nose for biological improvement formulated a theory (punctuated equilibria) that came to be associated with a radically different view of life. In Part 1 I introduced the adaptationist— Stephen Jay Gould— and explained why “biological improvement” played so large a role in his early thinking about evolution. In Part 2 I noted a “paradox”: that the advent of PE did little to shake Gould’s adaptationist and progressivist commitments— at least at first. I argued that the paradox vanishes once we realize that the original formulation of PE was wholly compatible with Gould’s early view of life, including the idea that improvement supplies the main vector of history in large taxa. But I left for Part 3 the task of saying why Gould came to relinquish this early set of ideas, and with a vengeance. How is it that PE came to serve as the “coordinating centerpiece… for a larger [set of]… concerns [in evolutionary theory]” (Gould 2002, 37), most notably, a twin-barreled critique of adaptationism and the concept of progress? And why did it only begin to play this role after 1977?
Stephen Jay Gould in Eleuthera, Bahamas, 1982. The object in his hand is a land snail in the genus Cerion
My answer to these questions will ascribe a large role to Steven Stanley (1941–), a paleontologist cast in much the same mold as Eldredge and Gould. Yet to forestall a misunderstanding I have encountered in discussing this work, I am not interested in entering any priority claims on Stanley’s behalf. Stanley saw, more clearly than Eldredge and Gould, that selection can be said to operate on species themselves, and especially on those features of species that favor high rates of speciation. But this is not to say that Stanley deserves sole credit for inventing “species selection,” nor even that he was the main architect of the new macroevolutionary theory of the 1980s. Eldredge and Gould inspired Stanley, who in turn stimulated Gould (and to a lesser extent Eldredge) to refine their thinking about evolutionary trends. This is the way things go. Complex ideas do not emerge fully-formed like Venus from the surf. Instead, the process of sharpening and articulating concepts is an extended one, which frequently involves a whole cast of characters working at cross purposes (e.g., Janssen and Renn 2015).
This essay will follow a simple plan. First, I will develop some context that is useful for understanding Gould’s change of mind in the late 1970s. Then, I will bring Stanley into the picture and say how his intervention stimulated Gould to see punctuated equilibria in a different, and broader, context. Finally, I will return to a wider focus and attempt to say how Gould’s reassessment of PE was related to other changes in his thought, most notably his souring on adaptationism.
If I may be autobiographical for a moment, this material is close to my heart. I wrote my very first paper back in 2017 on what I termed Stephen Jay Gould’s “first macroevolutionary synthesis.” This was the set of ideas, including Rudwickian paradigm analysis and gradal classification, that framed Gould’s early programmatic vision for evolutionary paleontology. Two years later I published a sequel of sorts (in fact, the papers had once been one long paper). This was called, “Macroevolution evolving: punctuated equilibria and the emergence of Stephen Jay Gould’s second macroevolutionary synthesis.” In the sequel I told part of the story that I will tell again here. But the story was never intended to stand on its own. It was always part of a larger narrative spanning the fall of Gould’s first macroevolutionary synthesis and the rise of its successor. Here I want to put some of these pieces back together. (And if I can spare anyone the labor of reading my gawky first paper, all the better.)
A Distinctively Paleontological Contribution
Stephen Jay Gould was never idle, but the mid-1970s were an especially busy time in his professional life. In 1970, just three years after arriving at Harvard, Gould laid out his vision for evolutionary paleontology in a paper, “Evolutionary paleontology and the science of form.” Then came “Punctuated equilibria,” and a pioneering attempt to use computers to simulate large-scale patterns in the history of life. In 1973, Gould began co-teaching a course on evolutionary theory with the population geneticist Richard Lewontin, recently hired away from the University of Chicago. And somehow, he found time to begin writing a new series of monthly essays in Natural History magazine, with a title that echoed both Darwin and George Gaylord Simpson: “This view of life.”
The first of 300 consecutive monthly essays that Gould wrote for Natural History magazine, published in January 1974. It explores one of Gould’s early preoccupations (and a theme central to his proposed “science of form”), the relationship between size and shape
Amid all this activity— and I have not even mentioned the Sociobiology controversy, which exploded in 1975— Gould changed his mind about evolution. Evolution is not a process directed in its main lines by natural selection honing the basic features of taxa. Instead, it is an altogether chancier thing, and one that is anything but progressive in its general aspect. So, why the change? The key to answering this question, I suggest, is to recognize that throughout his career, Gould was interested in raising the disciplinary standing of paleontology. It was not his only goal; Gould was at least as interested in being seen as the person who had raised the disciplinary standing of paleontology. (The claim that Gould pursued his own fame is not without warrant.) But to regard him exclusively as a man on the make is to miss a crucial bit of motivation, and one that helps make sense of his dramatic volte-face.
Invertebrate paleontology has never been a prestigious science, but for much of the twentieth century its reputation was in the gutter (Cooper 1958). A typical complaint was that it was no more than a “handmaiden to stratigraphy.” Since fossils help geologists tell time, and most stratigraphically useful fossils are invertebrates, expertise in invertebrate paleontology was a great aid to stratigraphic classification and correlation. But these are hardly the activities of which scientific reputations are made. In particular, very little research in invertebrate paleontology had any connection to the great questions of biology. J. Brookes Knight (1888–1960), an invertebrate paleontologist, put the point tartly in a 1947 presidential address to the Paleontological Society:
[What] we today call a paleontologist, particularly that jellylike variety without a backbone, incapable of standing erect on his own two feet, the invertebrate paleontologist, is not a paleontologist at all. He is a geologist, a stratigraphical or “soft- rock” geologist. He has considerable familiarity with invertebrate fossils, to be sure, but he is a geologist nevertheless. (Knight 1947, 284)
The problem was still around in the 1960s, when Martin Rudwick (1932–), then working as an invertebrate paleontologist, complained that “[paleontology had been] stunted throughout its existence by its subservience to the needs of stratigraphy”:
This [subservience] has hindered the mainstream of paleontological work from developing any genuinely biological attitude. The situation has certainly improved within the last decade, but even today what is so often missing is any imaginative awareness of fossils as the remains of organisms that were once alive. (Rudwick 1968, 35)
Even in 1980, invertebrate paleontologists continued to lament their subordination:
Invertebrate paleontology has cast its institutional allegiance with geology—more by historical accident than by current logic. When it operates as a geological discipline, paleontology has tended to be an empirical tool for stratigraphic ordering and environmental reconstruction. As a service industry [of academic and economic geology], its practitioners have been schooled as minutely detailed, but restricted experts in the niceties of taxonomy for particular groups in particular times. (Gould 1980, 98)
When Gould set out to reform paleontology, then, a consensus had long existed among would-be paleobiologists. First, they agreed that the science of (invertebrate) paleontology had been unjustly subordinated to the needs of stratigraphy. Second, they agreed that progress in paleontology required the cultivation of a genuinely biological attitude (whatever that meant). And third, they agreed that because the subordination of paleontology prevented the cultivation of this attitude, the future of paleontology hinged on its separation from stratigraphic geology, and the reassertion of its status as an autonomous biological science (Dresow 2023).
A plate from William Smith’s Strata Identified by Organized Fossils, showing the characteristic fossils of the “Oak-Tree Clay” (corresponding to the Kimmeridge Clay of modern nomenclature, middle Upper Jurassic). Images like this exemplify an approach to fossils that treats them as instruments for stratigraphic classification and correlation as opposed to the remains of once-living organisms
I have argued elsewhere that it is useful to view Gould’s early career as a series of attempts to make a distinctively paleontological contribution to evolutionary theory (Dresow 2019b). This was how he intended to break the chains lashing invertebrate paleontology to stratigraphy, and to reassert the former’s status as autonomous biological science. His first attempt was the science of form summarized in Part 1 of this essay. Then came punctuated equilibria, which I have argued was compatible with (and in a sense complimentary to) the science of form. Most radical of all was the “MBL project,” undertaken in collaboration with David Raup, T.J.M. Schopf, and Daniel Simberloff, and named after the Marine Biological Laboratory in Woods Hole where the group held their first meetings. Eventually he decided that the future belonged to PE. But this wasn’t evident at first, and for several years following Eldredge and Gould (1972) the development of PE took a backseat to the business at MBL (Sepkoski 2012).
Like the science of form, the MBL project staked its claim to significance on the promise of revolutionary change. The group’s second publication bore the bombastic subtitle “Towards a nomothetic paleontology” (Raup and Gould 1974). The word “nomothetic” was unfamiliar, but it was well-chosen. Nomothetic means “concerning general laws” (or something like that); so what the MBL group was promising was nothing less than a paleontology oriented toward “laws independent of time, space, or taxonomic group.” Not for them the drudgery of describing specimens, naming taxa, and reconstructing paleoenvironments. These were important activities, but they were unlikely to pull paleontology out of the scientific doldrums. More promising were the stochastic models that were all the rage in the bubbling field of population ecology. Might these be used to simulate the history of life, at least in its broadest outlines?
Simulated spindle diagrams from the first paper produced by the MBL group (from Raup et al. 1973). The letters (A–D) refer to different runs of the computer program, the numbers identify particular clades
That was the question the MBL team set itself to answering. And early indications were promising, especially when the history of life was rendered as a collection of spindle diagrams, which depict the relative diversity of higher taxa through time. In their debut publication, the MBL team showed that even relatively simple stochastic models can recover evolutionary patterns strikingly similar to those constructed on the basis of fossil compendia (Raup et al. 1973). It wasn’t clear what to make of this, and indeed the collaborators never agreed about how the simulations should be interpreted. Still, it was unexpected and exciting: new enough to scandalize traditional sensibilities while retaining a connection to tradition in its computer-rendered spindle diagrams. For someone looking to turn paleontology on its head, the whole thing must have been irresistible.
There is more to say about this, but it will have to wait. The key take-away from this section is that Gould had a career-long interest in raising the status of paleontology, and in the early 1970s this led him to pursue several projects aimed at demonstrating paleontology’s relevance to evolutionary theory. The most exciting of these was the MBL project, but Gould was also actively engaged in promoting his Rudwickian science of form. Anyway, PE was not at the center of his research program in the first half of the 1970s. One could even say that it occupied a position near the periphery. This was eventually to change, but only following the application of a well-placed external stimulus.
Steven Stanley and the “Decoupling” of Micro- and Macroevolution
Like Gould (who was his exact contemporary), Steven Stanley seems to have been shot out of a canon. Born in 1941, Stanley spent his childhood exploring the boulders and till of the Chagrin River Valley in Ohio. From there it was on to Princeton, where he studied under the redoubtable Alfred Fischer, and Yale, where he earned his PhD in 1968. His prolific output began in earnest in the 1970s. Probably his most impressive paper from that decade was a reinterpretation of Cope’s Law (roughly, the observation that body size tends to increase over the evolutionary history of a taxon). Stanley put this down to a tendency on the part of major taxa to arise at small body size relative to the optimum for an adaptive zone (Stanley 1973). His paper has since been cited over 700 times (not least by Gould, who eventually enlisted it in his campaign against the ubiquity of “progress” in evolution). However, it was not even Stanley’s most cited paper from the 1970s. Edging it by a couple hundred citations is “A theory of evolution above the species level,” which appeared in PNAS in 1975.
Steven Stanley alongside an image from Stanley (1972) showing the hypothetical derivation of a free-burrowing clam (D) by “progenesis” (truncated development) from a byssate ancestor (D). I will refer back to the image on the right in the final section of this essay
Stanley begins the paper with an interpretive claim. Taking his lead from Eldredge and Gould (1972), he writes that “the presence of a largely random process (speciation) between [micro- and macroevolution, or evolution within and above the species level, respectively] decouples them, [such] that large scale evolution is guided not by natural selection, but by [an analogous] process” (Stanley 1975, 646). “In this higher-level process,” he continues, “species become analogous to individuals, and speciation replaces reproduction” (648). The following remark, which explores the analogy between natural selection and what he terms “species selection,” is worth quoting at length.
Whereas, natural selection operates upon individuals within populations, a process that can be termed species selection operates upon species within higher taxa, determining statistical trends. In natural selection, types of individuals are favored that tend to (A) survive to reproduction age and (B) exhibit high fecundity. The two comparable traits of species selection are (A) survival for long periods, which increases chances of speciation and (B) tendency to speciate at high rates. Extinction, of course, replaces death in the analogy. (Stanley 1975, 648)
The thing to notice about all this is that it is PE— and especially the suggestion that morphological evolution is cramped into speciation events— that permits the analogy to go through. If species originate in geological instants and remain stable after that, it is conceptually straightforward to treat them as individuals. And if speciation is random (or undirected with respect to ongoing morphological trends), then one can speak meaningfully about there being a discontinuity between micro- and macroevolution. Crucially, it is this discontinuity that “decouples” micro- and macroevolution, and that recommends species selection as an explanation of the “overall course of evolution.” Previously it had been assumed that garden variety natural selection explains this pattern. But if speciation insinuates itself between events in populations and those in clades (i.e., events involving populations of species), then investigators must take seriously that macroevolutionary causation is sui generis. This was Stanley’s proposal in a nutshell.
Table 1 from Stanley (1975), summarizing the analogy between natural and species selection. The novelty of Stanley’s proposal is found in the bottom right corner, where the possibility of selection operating on rates of speciation is mooted
How much of this had Eldredge and Gould anticipated? To begin, the idea that speciation is “random” (or undirected with respect to ongoing evolutionary trends) was taken from Eldredge and Gould (1972). The same goes for the idea that a higher-level process is responsible for the directionality of (certain) evolutionary trends. Beyond that, however, things are murkier. Eldredge and Gould seem to say that trends arise when a species that varies in a certain direction gains an advantage, making it better able to hang on in an environment than its competitors. (This enables it to produce more “offspring” than its competitors, all things being equal.) But this seems to presuppose that what matters in the explanation of large-scale trends is phenotypic characteristics— basically, adaptations. Stanley's view is more general. Perhaps some trends are driven by the greater efficiency conferred by a key adaptation, which enables a lineage to access a new adaptive zone. But others may be driven by the greater ability of certain species to produce daughter species. Very widespread taxa, for example, might be especially fecund, but for reasons having little to do with particular phenotypic characteristics. If this is plausible, then we must say that selection sometimes operates on species in virtue of irreducible species-level properties. Stanley’s proposal countenances this possibility; Eldredge and Gould’s apparently does not.
All this is post hoc reconstruction, though. At the time, the differences between proposals were harder to spot (Dresow 2019a). Even Gould seems to have missed the crucial distinction in the early going. Writing just after Stanley’s PNAS paper, Gould complained that Stanley gave a name to a process “Eldredge and I chose explicitly not to christen” (Gould 1977a, 24). This is a priority claim meant to establish that the core of Stanley's proposal was already contained in Eldredge and Gould (1972). But the claim is only valid if the distinction between selection operating on species in virtue of the phenotypic characteristics of organisms, and selection operating on the irreducible features of species themselves, cuts no ice. To his credit, Gould soon recognized Stanley’s creative contribution, and even came to view selection on the irreducible features of species as the more promising form of species selection (e.g., Gould 1982, cf. Eldredge 2015).
The turning Point
I used the word “promising” at the end of the last section advisedly. What was most attractive about Stanley's construal of species selection was how promising it was. But what was promising about selection operating on the irreducible features of species? Precisely that “true species selection” (as Gould came to call it) was a macroevolutionary cause, operative on paleontological time scales, which had been discovered by paleontologists. Moreover, it was a cause that might explain some of the most important features of life's history— not the complex adaptations “which justly excite our admiration,” but instead what George Simpson called the “major features of evolution” (Simpson 1953). Assuming this panned out, it would be exactly what Gould had been looking for— a distinctively paleontological contribution to evolutionary theory. Further, it would be a contribution that incorporated PE as part of its internal logic. It is only because morphological evolution is cramped into “random” speciation events that macroevolution is decoupled from microevolution. And so, Gould would argue, PE takes its place as the linchpin of a hierarchically expanded theory of natural selection: “the most portentous and far-reaching reform of Darwinism in our generation” (Gould 1994, 6769).
This argument will be familiar to anyone who has browsed Gould’s final book, The Structure of Evolutionary Theory (2002). But he began assembling it much earlier, in the sequel to “Punctuated equilibria: an alternative to phyletic gradualism.” Called “Punctuated equilibria: the tempo and mode of evolution revisited,” the paper is largely a progress report on attempts to put PE to the test. But it also contains a long section on the theoretical implications of PE.* Here, Gould claims that PE supplies the basis for a new theory of macroevolution, which he terms “the speciation theory.” This is an elaboration of the framework sketched in Stanley (1975):
Wright’s analogy [comparing speciation with random mutation] represents the key to the claim that a new theory of macroevolution resides in the expression: punctuated equilibria + Wright’s rule = species selection… Previously, mutation and natural selection were regarded as fully sufficient to render macroevolution: one had only to extrapolate their action directly to longer times and higher taxa in large clades. But if we (1972) and Stanley (1975) are right, speciation interposes itself as an intermediate level between macroevolutionary trends and evolutionary events within populations. Species become the raw material of macroevolution… [and all] movement from micro- to macroevolution must be translated through the level of species by Wright’s grand analogy. (Gould and Eldredge 1977, 140)
[* Gould penned the 1977 paper in its entirety. Eldredge’s main contribution, he later recalled, was to stump for the inclusion of the word “Mode” in the title (Eldredge 2012).]
What does this look like in practice? Consider the classic paleontologist observation that “overspecialized groups” are especially prone to extinction. What explains this? An older explanation points to the increased morphological flexibility of (typically small) “unspecialized” forms, which allegedly immunizes these groups against extinction. But Gould and Eldredge speculate that “relative ability to speciate, not [increased] morphological flexibility, provides [the] interpretive key [to the phenomenon of ‘overspecialization’]” (Gould and Eldredge 1977, 140). Large bodied animals tend to live in small population that do not easily fracture. By contrast, “[small] animals maintain populations large enough to weather severe density-dependent mortality, while their limited mobility [as adults] and coarse-grained perception of the environment permit an easier separation into isolated subgroups” (141). Small-bodied species may thus be very good speciators, and if this is so, perhaps it is the case that the world has become full of small-bodied species for reasons having little to do with the morphological “overspecialization” of large-bodied taxa.
Gould and Eldredge’s table of the “determinants of evolutionary success in species and clades.” Note the similarity to Table 1 in Stanley (1975), reproduced above. And notice how Gould— always sensitive to the power of visual arguments— relegates “triumph over other species in direct competition” to the bottom right corner of the figure
In a similar vein, Gould and Eldredge observe that most paleontologists have explained the success of diverse and long-lived clades in terms of “good morphological design, fashioned and tested in competition against species of other clades” (Gould and Eldredge 1977, 143). (Indeed, this is close to what Gould himself thought only a few years before.) “But just as life history parameters of maturation time and reproductive effort have been used to explain success in ecological time, so must the macroevolutionary study of speciation rate be included in our study of successful clades. Especially speciose taxa can be predicted to be “r-strategists”: they will be taxa that are especially good at producing daughter taxa. (The “r” refers to the term for maximal growth rate in a general logistic growth model. r-strategists invest in population growth rate at the expense of parental care for individual offspring.) By contrast, especially long-lived taxa might be understood as macroevolutionary “K-strategists” (from the term for carrying capacity). If the analogy is apt, then the greatest evolutionary success stories might be best thought of as “the ‘supertramps’ of macrevolution” (145). Further, “[the] virtual irrelevancy, in many cases, of morphological superiority to a clade’s success may largely explain the puzzling observation that so few stories of increasing perfection in design can be read from the history of life” (144). (Compare this to Gould’s remark, made seven years before, that “The evolution of most major groups is… a history of mechanical improvement” (Gould 1970, 111).)
What is striking about Gould and Eldredge (1977) is that it appeared less than a year after Gould took umbrage at Stanley’s coinage of “species selection,” in a publication that displays Gould’s ongoing commitment to a view of evolution centered on adaptation and mechanical improvement (Gould 1977a). Gould and Eldredge (1977) thus marks the point at which Gould assimilated Stanley’s insight, and most significantly, when he realized that the decoupling of micro- and macroevolution stood to enshrine PE at the center of a major, paleontologically-inspired revision of evolutionary theory. It was self-serving, even self-aggrandizing, but it was not cynical— Gould really believed that PE unlocked a new tier of evolutionary causation. And once he convinced himself of this, a whole string of consequences followed in its train.
Dominoes Falling
The most conspicuous consequence was that Gould rapidly abandoned the other two projects that he had once regarded as promising sources of distinctively paleontological contributions to evolutionary theory. The science of form, in its original Rudwickian shape, was the first to fall. Once upon a time, Gould had regarded the experimental demonstration of mechanical improvement in large groups as the supreme goal of evolutionary paleontology. Yet by 1977, he was publicly remarking on the absence of clear instances of mechanical improvement in the fossil record. Three years later, he confessed with embarrassment how he once believed “that a simple enumeration of more and more cases [of good design] would yield new principles for the study of form” (Gould 1980, 101). This is an indictment of the methodological basis of his science of form, albeit scrubbed of any reference to its goal of documenting biological progress. He was free to make these remarks because, by 1980, the future of paleontology no longer hinged on the empirical demonstration of mechanical improvement in large taxa. Instead, it hinged on the decoupling of micro- and macroevolution via punctuated equilibria, and all that this entailed. As Gould wrote, “if species are irreducible inputs [to macroevolution], then paleontology wins its independence as a subject for the generation in testing of evolutionary theory” (107). Remarkably, though he had not seen it at first, PE had become a key pillar on which the autonomy of paleobiology rested.
Figure 2 from Gould (1970), described as “The compleat ostracode, Mechanocythere. Drawn for Richard H. Benson by L.B. Isham… [and meant to] underline the mechanistic thinking that most zoologists use… quite appropriate[ly].” Gould (1970) had a similar agenda. Paleontologists should think of animals on the analogy with machines if they wish to develop a “science of adaptation” worthy of the name
The other project was the MBL project, and here too Gould was in the process of turning away from it in the late 1970s. There were internal differences among the MBL collaborators. Tom Schopf had become increasingly evangelical about his vision of a stochastic paleontology organized around a set of “gas laws,” and Gould was among the colleagues he was in the process of alienating. It was one thing to observe that major features of life’s history can be reproduced using stochastic models. It was quite another to imply that the processes responsible for generating those patterns resembled a turn at the roulette wheel. The latter was Schopf’s position. Gould could not accept it. Nor did he support the particular way that Schopf moralized about randomness and determinism in the history of life. Schopf compared the scientist who says that trilobites were out-competed to the person who says that some biological races are inherently superior to others (Sepkoski 2012). But this was a strategy designed to win few friends. Whatever the legitimate uses of stochastic models, they were not racks for extracting purity commitments to the one true stochastic religion.*
[* There were technical issues with the MBL model too. Steven Stanley (of all people) published a paper in 1981 that showed that stochastic models fail to reproduce realistic clade dynamics when appropriately scaled with species-level data (Stanley et al. 1981). This dealt a near-lethal blow to the original aspirations of the MBL team.]
I must be careful. When I say that Gould turned away from the MBL project in the late 1970s I do not mean that he withdrew support from the project of using models to understand the history of life. What I mean is that he distanced himself from the project of using stochastic models to simulate the history of life in silico using only a few basic parameters. In a 1980 paper in Paleobiology, Gould threw his weight behind the project of using equilibrium models to represent the diversification of marine life in the Phanerozoic. This was a project that had been pioneered by Gould’s former graduate student (and a collaborator on some of the MBL papers), Jack Sepkoski. The project, however, belonged to Sepkoski, not to Gould. It also differed from the MBL project in making extensive use of empirical data. Anyway, the point I wish to make is that by the end of the 1970s, the dream of the MBL project was effectively dead, at least in its most radical form. Gould seemed to have lost little sleep over this, and why shouldn’t he have? With his new “speciation theory” in tow, there was no longer a need to pin the reforming dreams of paleobiology to the fortunes of the MBL model.
* * *
So much for the question of how PE edged out the science of form and the MBL project. But these remarks fall short of explaining why Gould turned against adaptationism after about 1977. What they show is that there was an important strategic dimension to Gould’s anti-adaptationism. Before 1977, Gould had skin in the adaptationist game. After 1977, he divested, and this freed him to explore the value of emphasizing other parts of evolution, like the “spandrels” of Gould and Lewontin (1979). It is noteworthy that the first glimmerings of this critique are already present in Gould and Eldredge (1977). Here Gould writes that gradualism “is not the only prior prejudice constraining paleontological thought.” Just as important is “our propensity for explaining all questions of diversity and success in terms of morphological adaptation.” Such a remark would have been unthinkable even a few short years before. So to raise the question one last time: what happened?
Quite a bit, frankly, but two things should be mentioned before I conclude this interminable essay. The first was a modeling result, which Gould subsequently acknowledged to have shaped his intuitions about directional change. It came out of the MBL project, and specifically the attempt to simulate random change and morphology in a “phyletic context” (Raup and Gould 1974). The question Gould and Raup were interested in was whether such a simulation would generate familiar evolutionary patterns, including patterns of directional change. What they found was that it did indeed generate such patterns. And while Gould was at first reluctant to see this as a challenge to orthodoxy, he later revealed that it worked a slower alchemy on his thought (Gould 2002, 43). (Let me add that Gould’s reluctance to interpret this result as a challenge to orthodoxy is more evidence that he had yet to acquire the intuitions associated with the decoupling thesis. Since Eldredge and Gould (1972) treated individual-level natural selection as the locomotive of evolutionary trends, Raup and Gould’s result didn’t reinforce the picture of evolution associated with PE— it challenged it.)
A figure from Raup and Gould (1974) showing a clade of randomly generated morphologies (“triloboids”). If this figure depicted an actual case, the authors remark, “[the pattern] would probably not stand out as unusual.” (Note: the images of individual triloboids here represent the average morphologies of whole clades, each composed of ten lineages)
The second and more important thing that shook Gould’s adaptationism was Ontogeny and Phylogeny. This was Gould's first professional book, completed in 1975 or early 1976 and published in 1977. It is sometimes described as an attack on adaptationist biology in the spirit of Gould and Lewontin (1979).* But the characterization is wildly off-base. Ontogeny and Phylogeny is adaptationist to its marrow. Gould said as much in subsequent reflections, where he described the book as an attempt to show “that all [changes in developmental rate or timing] can be interpreted as adaptations, once the proper ecological correlations are established” (Gould 1988, 11). The likeliest reason for this misunderstanding is that people tend not to read the whole book. Part 1 of the book is a history of recapitulationism— the idea that ontogeny recapitulates phylogeny. This is the part that people read. Part 2 is a technical discussion of heterochrony, which wears its adaptationist colors on its sleeve. It is seldom read.
[* For example, the historian Joe Cain has described Ontogeny and Phylogeny as “attack[ing] adaptationism and trumpet[ing] the approach to developmental biology [that Gould] advocated against genetic reductionism.”]
Part 2 of Ontogeny and Phylogeny has several goals: for example, to clean up the terminology surrounding “heterochrony” (changes in developmental rate and timing) and to defend neoteny as an important factor in human evolution. (“Neoteny” is a kind of heterochrony involving delayed somatic development.) But perhaps Gould’s main goal in Part 2 is to say when particular kinds of heterochrony will be adaptively beneficial. So he observes that “progenesis” (truncated development) will be favored in unstable environments that impose strong selection for rapid maturation and quick generational turnover. Likewise, neoteny will be favored in stable environments that permit the fine-tuning of morphological adaptations. The case is cogently argued, as far as it goes. But Gould goes further, arguing that developmental changes— while arising for immediate adaptive reasons— also have macroevolutionary consequences. Most important is the macroevolutionary deployment of progenesis, which gains its power “by presenting to future selective contexts a… mosaic of juvenilized and adult characters in an organism freed from rigid morphological monitoring” (Gould 1988, 10). Progenesis thus represents a pathway to major evolutionary innovations because where progenesis is adaptively favored (in unstable environments) selection will not be operating directly on morphology. Instead, it will be acting on developmental timing: something that permits the morphological novelties associated with truncated development to escape selective scrutiny. (For an illustration of this, see the image in the section “Steven Stanley and the ‘decoupling’ of micro- and macroevolution.”)
But so what? Isn’t this just so much adaptationism, again? Yes and no. Yes, the Gould of Ontogeny and Phylogeny remains preoccupied with the adaptive basis of morphology. But whereas he had earlier conceptualized the relationship between adaptation and natural selection as a simple one (with selection operating directly on morphology to produce adaptive improvement), here the picture is more nuanced. Sometimes selection operates directly on morphology to produce adaptive improvement. Yet other times, major evolutionary changes will be produced by selection operating on developmental timing, with fortuitous morphological consequences. The thing to notice is that if selection and morphological change are sometimes decoupled, then the conceptual link between natural selection and morphological change is dissolved. Natural selection will not be directly responsible for all the most important changes in the fossil record. What had one seemed a truism— that the changes studied by paleontologists should be explained by selection acting on morphology— had been downgraded to a hypothesis. With this realization, the road to a strategic non-adaptationism lay open.
* * *
Let me close with a small thought. Stephen Jay Gould was never afraid to admit that, as a young scientist, he had been an adaptationist. In his final book, he went so far as to describe Gould (1970) as “a ringing paean to selectionist absolutism, buttressed by the literary barbarism that a ‘quantifunctional’ paleontology, combining the best of biometric and mechanical analyses, could prove panadaptationism even for fossils that could not be run through the hoops of actual experiments” (Gould 2002, 41).
Gould was less forthcoming, though, about his volte-face on biological improvement. Once, the experimental demonstration of improvement had been central to his vision for evolutionary paleontology. Even in Ontogeny and Phylogeny, discussions of “progress” can be found in his writings without accompanying scare quotes or explicit criticisms. So, what accounts for the difference? Perhaps there is no deep reason, and Gould simply never felt the need to exorcize that particular demon. Or perhaps he knew that some admissions cut too close to the quick.
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