EXCERPTS FROM GOULD’S LARGER BOOK
[NOTE: This posthumously-published book contains material reprinted from Chapters 1 and 9 of ‘The Structure of Evolutionary Theory.”]
The Introduction states, “punctuated equilibrium stands for a larger and coherent set of mostly iconoclastic concerns… As I began my professional preparation for a career in paleontology … [a] vague dissatisfaction coagulated into two operational foci of discontent. First… I became deeply troubled by the Darwinian convention that attributed all non-gradualistic literal appearances to imperfections of the geological record… Second, I became increasingly disturbed that, at the higher level of evolutionary trends within clades, the majority of well documented examples… have never been adequately explained in the terms demanded by Darwinian convention---that is, as adaptive improvements of constituent organisms in anagenetic sequences. Most so-called explanations amounted to little more than … plausible claims without tested evidence, whereas other prominent trends couldn’t even generate a plausible story in adaptationist terms at all.
“As [Niles] Eldredge and I devised punctuated equilibrium, I did use the theory to resolve these two puzzles to my satisfaction, and each resolution… led to my two major critiques of the first two branches of the essential triad of Darwinian central logic… By accepting the geologically abrupt appearance and subsequent extended stasis of species as a fair description of an evolutionary reality… we soon recognized that species met all criteria for definition and operation as genuine Darwinian individuals in the higher-level domain of macroevolution---and this insight … led us to concepts of species selection in particular and, eventually, to the full hierarchical model of selection as an interesting theoretical challenge and contrast to Darwinian convictions about the exclusivity of organismal selection.” (Pg. 1-3)
He notes “a primary inference of punctuated equilibrium---that a local pattern of abrupt replacement does not signify macromutational transformation in situ, but an origin of the later species from an ancestral population living elsewhere, followed by migration into the local region,” (Pg. 17-18)
He points out “the cardinal and dominant fact of the fossil record… the great majority of species appear with geological abruptness in the fossil record and then persist in stasis until their extinction… the last remnants of a species usually look pretty much like the first representatives… Paleontologists have always recognized the longterm stability of most species, but we had become more than a bit ashamed by this strong and literal signal, for the dominant theory of our scientific culture told us to look for the opposite results of gradualism as the primary empirical expression of every biologist’s favorite subject—evolution itself.” (Pg. 19)
He summarizes, “the potentially reformative role of punctuated equilibrium resides in .. [that it] merely honored the firmest and eldest of all paleontological observations---the documentable stasis of most fossil morphologies---by promoting this pattern to central recognition as an expected result of evolution’s proper expression at the scale of geological time.” (Pg. 38) He continues, “punctuated equilibrium holds that the great majority of species… originate in geological moments (punctuations) and then persist in stasis throughout their long durations… species meet all definitional criteria for operating as Darwinian individuals… in the domain of microevolution.” (Pg. 40) Later, he adds, “punctuated equilibrium makes its major contribution to evolutionary theory, not by revising evolutionary mechanics, but by individuating species…” (Pg. 58)
He explains, “the theory of punctuated equilibrium adopts a very conservative position. The theory… merely takes a standard microevolutionary model and elucidates its expected expression when properly scaled into geologic time. This scaling, however, did provoke a radical reinterpretation of paleontological data—for we argued that the literal appearance of the fossil record, though conventionally dismissed as an artifact of imperfect evidence, may actually be recording the workings of evolution.” (Pg. 54)
He suggests, “If evolutionary rate correlates primarily with frequency of speciation---the cardinal prediction of punctuate equilibrium---then living fossils may simply represent those groups … that have persisted through geological time at consistently and varyingly low species diversity… and have therefore never experienced substantial opportunity for extensive change at this level.” (Pg. 101-102)
He says, “the stress placed by punctuated equilibrium upon the phenomenon of stasis may emerge as the theory’s most important contribution to evolutionary science… punctuated equilibrium largely ‘created’ the category of stasis as an important item in evolutionary theory through a four-step process of (1) defining stasis as a positive ‘thing’ with properties and boundaries… rather than an unnamed and unrecognized absence of evolution; (2) bringing stasis to visibility as the expectation of a particular theory of evolutionary modalities; (3) suggesting methods for the active and rigorous study of stasis, so that the concept could be operationalized as a subject for empirical research; and (4) granting interest and importance to stasis as a controversial topic with broad implications for revising traditional modes of thought in evolutionary theory.” (Pg. 172-173)
He argues, “if stasis merely reflects excellent adaptation to environment, then why do we frequently observe such profound stasis during major climatic shifts like ice-age cycles… or through the largest environmental change in a major interval of time…? More importantly, conventional arguments about stabilizing selection have been framed for discrete populations on adaptive peaks, not for the TOTALITY of a species---the proper scale of punctuated equilibrium.” (Pg. 176)
He acknowledges, “I now believe that these criticisms, with respect to the issue of stasis, in paleospecies through geological time, were largely justified—and that the theme of constraint, while not irrelevant to the causes of stasis in punctuated equilibrium, does not play the strong role that I initially advocated.” (Pg. 179)
He states, “[if] stasis emerges as an active norm, not merely a passive consequence… then evolutionary change itself must be reconceptualized as the infrequent breaking of a conventional and expected state, rather than as an inherent and continually operating property of biological materials, ecologies, and populations.” (Pg. 184-185)
He says, “[I] mean to assert the hypothesis of no overall preference for increasing complexity among items added to the distribution… I do not deny, of course, that individual lineages in such systems may develop increasing complexity for conventional adaptive reasons… why should we target increasing complexity as a favored hypothesis for a general pattern in the history of life?” (Pg. 203)
He admits, “if I were to cite any one factor as probably the most important among the numerous influences that predisposed my own mind toward joining Niles Eldredge in the formulation of punctuated equilibrium, I would mention my reading, as a first-year graduate student in 1962, of one of the 20th century’s most influential works at the interface of philosophy, sociology and the history of ideas; Thomas S. Kuhn’s ‘The Structure of Scientific Revolutions.’” (Pg. 283)
He summarizes, “I can at least assert that punctuated equilibrium unites three definitive themes---the three legs of my tripod of support for an expansion of Darwinian theory, thereby leading me to conclude that an empirically legitimate and logically sound structure does encompass and unite these three arguments into a coherent and general reformulation and extension of the Darwinian paradigm: the hierarchical theory of selection on leg one, the structuralist critique of Darwinian functionalism and adaptationism on leg two, and the paleontologist’s conviction (leg three) that general microevolutionary processes and mechanisms cannot be fully elucidated by uniformitarian extrapolation from the smallest scale of our experiments and personal observations.” (Pg. 287)
He concludes, “Punctuated equilibrium has proven its mettle in: 1. Elucidating and epitomizing what may be the primary process of a distinctive level in the evolutionary hierarchy: the role of species as Darwinian individuals… 2. Defining … the issue of stasis as a subject for study… 3. Stressing that level-bound punctuational breaks preclude the prediction or full understanding of extensive temporal change from principles of anagenetic transformation at the lowest level… thus emphasizing contingency and denying extrapolationist premises and methodologies.” (Pg. 287-288)
For Gould’s “last word” on punctuated equilibrium, this book will be “must reading” for students of evolutionary theory.