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Macroevolution: Pattern and Process
In Macroevolution, Steven Stanley addresses, from a paleobiologist's perspective, the question of whether punctuated equilibria or gradualism offers the best account of the history of life. Punctuated equilibria, a view popularized by Stephen Jay Gould among others, holds that species remain evolutionarily static for long periods of time and undergo substantial genetic changes and develop new, primarily adaptive, strategies during speciation. In contrast, gradualism views large-scale changes as the result of continual and successive small-scale changes. Coming down on the side of those who favor the model of punctuated equilibria, Stanley argues that only "quantum speciation" (speciation that is rapid and radically divergent) can explain the story of life revealed in the fossil record; macroevolutionary trends, he contends, can be explained by selection among species and, to a lesser extent, by phylogenetic drift and directed speciation.
370 pages, Paperback
First published November 1, 1979
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January 16, 2025
A SUPPORTER OF ‘PUNCTUATED EQUILIBRIUM’ LOOKS AT ‘MACRO’ CHANGES
Paleontologist and evolutionary biologist Steven Stanley wrote in the Preface to this 1979 book, “during the past few years, I have found myself … bringing fossil data to bear on biologic questions… relating to the process of evolution… I have come to believe that paleontologic data tell us things about evolution that have not gained general acceptance through … the Modern Synthesis. The fossil record… is more instructive in the field of evolution than many have believed. Here, perhaps, is the fundamental message of this book.”
He states, “the role of paleontology in evolutionary research has been defined narrowly because of a false belief… that the fossil record is woefully incomplete. Actually, the record is of sufficiently high qualify to allow us to undertake certain kinds of analysis meaningfully as the level of the species.” (Pg. 1)
He observes, “A gradualist claiming that phyletic evolution has been responsible for most divergence in the great lakes of Africa would be hard pressed to explain the widespread persistence of primitive species. How can ancestral forms remain unchanged when they are supposed to have evolved phyletically into more specialized forms? The gradualist’s only option would be to claim that some lineages have evolved incredibly rapidly while others have remained static… The punctuational model provides a much less perplexing explanation for the persistence of ancestral forms. Its basic tenet that lineages in general evolve slowly provides a ready explanation for the persistence of ancestral forms… specialized species that have budded off in stepwise fashion from the primitive forms.” (Pg. 47)
He states, “The view that virtually all stratigraphic sections contain gaps that disguise a gradualistic phylogeny seems to me to reflect little thought about the nature of the stratigraphic column. To be sure, the column is riddled with hiatuses, but the critical question is largely one of scale.” (Pg. 90) Later, he adds, “If the gradualistic model were valid, numerous genetic transitions should be documented in the thousands of invertebrate lineages that have been traced through spans of 5 to 10 [million years], yet such transitions are rarely discerned.” (Pg. 100)
He argues, “It might be claimed that in transferring the evaluation of living fossils to a punctual framework, I am simply switching the problem … Why should a lineage… almost cease to cast off descendants over a long span of geologic time. I find the question in no way perplexing… adverse conditions more readily stifle speciation than they cause the extinction of large, established species… If component lineages are characteristically long-lived, however, the resulting co-occurrence of longevity and low rate of speciation might be explained in part by the fact that both traits characterize species that disperse readily… Of course, many living fossil forms are not widespread, but occupy geographic refugia.” (Pg. 131)
He suggests, “the absence of evidence of substantial diversification and antiquity… of the bear-panda transition… leaves little doubt, that very few speciation events were involved in the origin of the family or subfamily of the giant panda. In fact, it seems possible that a single event of quantum speciation accomplished the transition.” (Pg. 138)
He explains, ‘One of the strongest strands in favor or hopeful monsters in recent years is… higher plants… we can note that it is to be expected that bizarre morphological features will be fixed more frequently within plants than within animals.” (Pg. 160)
He notes, “[Stephen Jay] Gould and [Niles] Eldredge have accepted my phrase ‘species selection.’ … In order to forestall possible objections … I offer the following justification. My opinion is perhaps most effectively supported by historical considerations. For propounding his concepts of macromutation and hopeful monsters, [Richard] Goldschmidt was ostracized by adherents of the Modern Synthesis. His ideas were considered utterly non-Darwinian. It must be appreciated, however, that, if correct, his views today would easily be accommodated within the punctuational model, albeit in its most extreme form. The point is that Goldschmidt’s ideas actually imply that transpecific trends should be guided by species selection. What does ‘hopeful monster’ describe if not a new form that might succeed or fail as an ancestral species? Both a random direction of speciation and a severe form of species selection are tacitly asserted here.” (Pg. 193)
He says, “Even if major transitions have occurred by way of many generations, it is unnecessary to invoke wholesale environmental change… A deus ex machina quality places many alleged evolutionary controls---especially those postulated in past decades---in the realm of expedient, farfetched speculation. Thus, I suggest that before invoking general environmental change, we should consider major transitions in the context of punctuational opportunism within heterogeneous environments.” (Pg. 207)
He asserts, “It is evident that much ingenuity has gone into devising of hypotheses to account for the prevalence of sex. The fact such ingenuity has been required engenders the suspicion that something is amiss…. The simple fact is that the gradualistic model has not been able, comfortably, to accommodate sexuality. All of the explanations outlined here offer potential reasons for sexuality being of some value. However, none reasonably accounts for its overwhelming dominance among eukaryotes, and none has passed empirical tests… Moreover, there is evidence that many asexual higher organisms are by no means maladaptive.” (Pg. 220)
He asks, “What happens to a taxon after being decimated by mass extinction? … the nature of species selection must differ among higher taxa according to the relative impact of competition and predation upon component species. These interactions should also exert an influence upon evolutionary response to mass extinction. The basic point here is that for a taxon in which interspecific competition is severe, mass extinction removes the major constraint on diversification. Following a sudden extinction, we would expect diversity to rebound rapidly. I have referred to such a taxon as having an ‘elastic’ quality…” (Pg. 283-284)
He suggests, “It is not immediately obvious why within the evolution of mammals there occur distinctive pulses of radiation embodies in genera. A reasonable hypothesis would be that, owing to behavioral interactions, particular geographic regions can accommodate only small numbers of congeric species.” (Pg. 287-288)
He summarizes, “The pronounced variation among taxa in rate of speciation and rate of extinction has important consequences. Assuming that fluctuations in these rates are proportional to original values, we can predict that taxa characterized by high rates will exhibit phylogenic instability (frequent mass extinction). This prediction is borne out by the high incidence of mass extinction for terrestrial tetrapods, especially those of large body size, and for trilobites, ammonites, and graptolites. Bivalves and gastropods, which have much slower turnover rates, have suffered far less from mass extinction.” (Pg. 299)
This book will be of great interest to those studying evolutionary theory.
Paleontologist and evolutionary biologist Steven Stanley wrote in the Preface to this 1979 book, “during the past few years, I have found myself … bringing fossil data to bear on biologic questions… relating to the process of evolution… I have come to believe that paleontologic data tell us things about evolution that have not gained general acceptance through … the Modern Synthesis. The fossil record… is more instructive in the field of evolution than many have believed. Here, perhaps, is the fundamental message of this book.”
He states, “the role of paleontology in evolutionary research has been defined narrowly because of a false belief… that the fossil record is woefully incomplete. Actually, the record is of sufficiently high qualify to allow us to undertake certain kinds of analysis meaningfully as the level of the species.” (Pg. 1)
He observes, “A gradualist claiming that phyletic evolution has been responsible for most divergence in the great lakes of Africa would be hard pressed to explain the widespread persistence of primitive species. How can ancestral forms remain unchanged when they are supposed to have evolved phyletically into more specialized forms? The gradualist’s only option would be to claim that some lineages have evolved incredibly rapidly while others have remained static… The punctuational model provides a much less perplexing explanation for the persistence of ancestral forms. Its basic tenet that lineages in general evolve slowly provides a ready explanation for the persistence of ancestral forms… specialized species that have budded off in stepwise fashion from the primitive forms.” (Pg. 47)
He states, “The view that virtually all stratigraphic sections contain gaps that disguise a gradualistic phylogeny seems to me to reflect little thought about the nature of the stratigraphic column. To be sure, the column is riddled with hiatuses, but the critical question is largely one of scale.” (Pg. 90) Later, he adds, “If the gradualistic model were valid, numerous genetic transitions should be documented in the thousands of invertebrate lineages that have been traced through spans of 5 to 10 [million years], yet such transitions are rarely discerned.” (Pg. 100)
He argues, “It might be claimed that in transferring the evaluation of living fossils to a punctual framework, I am simply switching the problem … Why should a lineage… almost cease to cast off descendants over a long span of geologic time. I find the question in no way perplexing… adverse conditions more readily stifle speciation than they cause the extinction of large, established species… If component lineages are characteristically long-lived, however, the resulting co-occurrence of longevity and low rate of speciation might be explained in part by the fact that both traits characterize species that disperse readily… Of course, many living fossil forms are not widespread, but occupy geographic refugia.” (Pg. 131)
He suggests, “the absence of evidence of substantial diversification and antiquity… of the bear-panda transition… leaves little doubt, that very few speciation events were involved in the origin of the family or subfamily of the giant panda. In fact, it seems possible that a single event of quantum speciation accomplished the transition.” (Pg. 138)
He explains, ‘One of the strongest strands in favor or hopeful monsters in recent years is… higher plants… we can note that it is to be expected that bizarre morphological features will be fixed more frequently within plants than within animals.” (Pg. 160)
He notes, “[Stephen Jay] Gould and [Niles] Eldredge have accepted my phrase ‘species selection.’ … In order to forestall possible objections … I offer the following justification. My opinion is perhaps most effectively supported by historical considerations. For propounding his concepts of macromutation and hopeful monsters, [Richard] Goldschmidt was ostracized by adherents of the Modern Synthesis. His ideas were considered utterly non-Darwinian. It must be appreciated, however, that, if correct, his views today would easily be accommodated within the punctuational model, albeit in its most extreme form. The point is that Goldschmidt’s ideas actually imply that transpecific trends should be guided by species selection. What does ‘hopeful monster’ describe if not a new form that might succeed or fail as an ancestral species? Both a random direction of speciation and a severe form of species selection are tacitly asserted here.” (Pg. 193)
He says, “Even if major transitions have occurred by way of many generations, it is unnecessary to invoke wholesale environmental change… A deus ex machina quality places many alleged evolutionary controls---especially those postulated in past decades---in the realm of expedient, farfetched speculation. Thus, I suggest that before invoking general environmental change, we should consider major transitions in the context of punctuational opportunism within heterogeneous environments.” (Pg. 207)
He asserts, “It is evident that much ingenuity has gone into devising of hypotheses to account for the prevalence of sex. The fact such ingenuity has been required engenders the suspicion that something is amiss…. The simple fact is that the gradualistic model has not been able, comfortably, to accommodate sexuality. All of the explanations outlined here offer potential reasons for sexuality being of some value. However, none reasonably accounts for its overwhelming dominance among eukaryotes, and none has passed empirical tests… Moreover, there is evidence that many asexual higher organisms are by no means maladaptive.” (Pg. 220)
He asks, “What happens to a taxon after being decimated by mass extinction? … the nature of species selection must differ among higher taxa according to the relative impact of competition and predation upon component species. These interactions should also exert an influence upon evolutionary response to mass extinction. The basic point here is that for a taxon in which interspecific competition is severe, mass extinction removes the major constraint on diversification. Following a sudden extinction, we would expect diversity to rebound rapidly. I have referred to such a taxon as having an ‘elastic’ quality…” (Pg. 283-284)
He suggests, “It is not immediately obvious why within the evolution of mammals there occur distinctive pulses of radiation embodies in genera. A reasonable hypothesis would be that, owing to behavioral interactions, particular geographic regions can accommodate only small numbers of congeric species.” (Pg. 287-288)
He summarizes, “The pronounced variation among taxa in rate of speciation and rate of extinction has important consequences. Assuming that fluctuations in these rates are proportional to original values, we can predict that taxa characterized by high rates will exhibit phylogenic instability (frequent mass extinction). This prediction is borne out by the high incidence of mass extinction for terrestrial tetrapods, especially those of large body size, and for trilobites, ammonites, and graptolites. Bivalves and gastropods, which have much slower turnover rates, have suffered far less from mass extinction.” (Pg. 299)
This book will be of great interest to those studying evolutionary theory.
December 8, 2009
Stanley get his message across "Punctuated equilibrium is how evolution functions." He could have been more brief, however. Oh, and his attitude of using punk eek to explain all evolutionary change is short sighted.
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