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The New Evolutionary Timetable First Printing edition by Stanley, Steven M. (1981) Hardcover
Describes recent theories about the tempo of evolutionary change and discusses their implications concerning the evolution of human beings
Hardcover
First published October 1, 1981
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January 16, 2025
MyA ‘PUNCTUATIONALIST’ EXPLANATION OF EVOLUTION, AND EVEN SOME JABS AT DARWIN
Paleontologist and evolutionary biologist Steven Stanley wrote in the Preface to this 1981 book, “What I describe in this book is evidence that evolution is not quite what nearly all of us thought it to be a decade of two ago. This evidence comes largely from the record of fossils---a record that until recently was not well scaled against absolute time. The record now reveals that species typically survive for a hundred thousand generations, or even a million or more, without evolving very much. We seem forced to conclude that most evolution takes place rapidly, when species come into being by the evolutionary divergence of small populations from parent species. After their origins, most species undergo little evolution before becoming extinct. It is only fair to point out that, while this ‘punctuational’ view has displaced the traditional ‘gradualistic’ view in the minds of many evolutionists, there remain dissenters… This book is not designed to build a rigorous case for the punctuational model of evolution---the goal of my more technical volume, ‘Macroevolution’ Pattern and Process.’ Rather, in the present book I attempt to give the interested non-specialist access to the punctuational view and its implications… I also explore the history of the traditional, gradualistic view. Among the most fundamental questions here is why Charles Darwin was a gradualist.” (Pg. xv)
He states in Chapter 1, “human evolution has apparently followed a stepwise course, with important biological change occurring as one species has branched rapidly from another. The fossil record of horses also testifies to an episodic tempo for evolution, and this is particularly notable because for decades the record of ancient horses was heralded as the classic illustration of gradual transformation… Although this fossil record, like all others, is incomplete, so that it fails to document the full history of the horse family, one of its striking revelations is great evolutionary stability for tiny dawn horses… Horses of the modern Equus type obviously evolved rapidly, and apparently for this reason their origin is not documented by known fossil evidence.” (Pg. 4-5)
He continues, “Thus, the new message offered by ancient remains … is that evolution has occurred episodically. Most change has taken place so rapidly and in such confined geographic areas that it is simply not documented by our imperfect fossil record. The resulting view of evolution has become known as the punctuational model, while the contrasting traditional view has been labeled the gradualistic model… The punctuational view implies… that evolution is often ineffective at perfecting the adaptations of animals and plants; that there is no real ecological balance of nature; that most large-scale evolutionary trends are not produced by the gradual reshaping of established species, but are the net result of many rapid steps of evolution, not all of which have moved in the same direction…” (Pg. 5)
He recounts, “What, above all else, has led me to adopt the punctuational view of evolution is the simple observation that chronospecies---lineage segments that embrace little total evolutionary change---last for remarkably long intervals of geological time. In other words, it takes a very long time for a species, once established, to evolve enough to deserve a new name. On the other hand, dramatically new forms of life (species so novel as to require recognition as new genera and families, for example) spring up quite suddenly on a geological scale of time.” (Pg. 15)
He explains, “Darwin capitalized on the fact that the alteration of stages of development often comes late in the history of an embryo, when the animal is approaching the time when it will have to assume its specialized behavior in the outside world…. It was easy for Darwin to see how evolution might have left the earliest stages almost unchanged. On the other hand, why would a creating divinity force all vertebrate beings through the same series of shapes before allowing them to diverge and assume the shapes associated with their postnatal habits?” (Pg. 38)
He continues, "Darwin also cited as evidence structures that we would now term ‘vestigial.’ These are rudiments that seem to serve no present function but that resemble more fully developed, functioning organs in other animals. Some examples are striking. The poorly developed pelvic bones and hind limbs of certain snakes do not fit the animal’s basic body plan, but can easily be accounted for as vestiges of ancestral organs not yet fully lost through evolution… How, Darwin reasoned, could any creator of a perfect global system have been so wasteful or imprecise in his production?” (Pg. 38)
He goes on, “Darwin … remained saddled with the contemporary concept of blending inheritance. This meant that in his day discrete units of genetic inheritance were unrecognized… Given a false belief in blending inheritance, it becomes difficult to imagine how even valuable new adaptations can come to prevail; with every breeding they will be averaged with others. How could selection possibly overcome such dilution instead of becoming blended into oblivion? Darwin… was deeply disillusioned by his inability to extricate his theory from this problem. He could have escaped by focusing on evolution within very small populations isolated by geographic or reproductive barriers… unfortunately, Darwin apparently overlooked this crucial point.” (Pg. 50-51)
He reports of a test he conducted: “I have called the test outlines the test of living fossils… I have tried to include in the test all narrow branches for which we have a fairly good fossil record. The critical point is this: I have yet to uncover one of these that displays marked evolutionary change. Living fossils have represented a thorny puzzle in the traditional, gradualistic scheme of evolution. If natural selection is constantly reshaping species in significant ways, why have some species been almost immune to the process?... These conflicting conjectures on ecological breadth illustrate the dilemma in which gradualism has been trapped by living fossils… The punctuational model provides us with the explanation… The punctuational model … predicts that even the persistent small groups will tend to exhibit little evolution because, however long they may have existed, they have undergone little speciation---and speciation is where most evolution occurs.” (Pg. 85-86)
He observes, “We know that after the demise of the dinosaurs the world was available for occupancy by mammals. Nonetheless, why should mere ecological opportunity cause any well-established species to abandon its way of life for an entirely new one?... Expanded ecological opportunity would be expected to produce great diversification… diversification proceeds by the sprouting off of new species from already established species---by adaptive radiation---and this, of course, brings us to the punctuational scheme of evolution… The new evidence for the stability of early Cenozoic species forces us to focus upon change by speciation involving small populations. Quantum speciation becomes our logical solution to the problem of the great mammalian radiation.” (Pg. 94-96)
He reiterates, “Example after example strengthens the case that rapid evolution is restricted to small populations. For large populations of the sort that constitute the species living all around us today, sluggish change is the norm---much more sluggish change than all but a few modern biologists have envisioned.” (Pg 101)
He points out, “Unfortunately, circular reasoning crept into the evaluation of the [fossil] record. Darwin made elaborate claims that fossil data were too sparse ever to support his gradualistic scheme, yet his condemnation of the record was not based on objective observation. About this, he was quite open in the ‘Origin’… ‘I do not pretend that I should ever have suspected how poor a record of the mutations of life… had not the difficulty of our not discovering innumerable transitional links between the species which appeared at the commencement and close of each formation, pressed so hardly on my theory.’ In other words, Dargin had deduced the incomplete nature of the fossil record from his theory.” (Pg. 105)
He comments about cichlid fishes in Lake Victoria: “Here we have a strong hint of what is important for the occurrence of quantum speciation: ecological opportunity. Given an opportunity like that of the cichlid fishes… most groups of animals or plants would diversify rapidly, yet some groups … display a tendency to undergo particularly spectacular radiations with great frequency.” (Pg. 119)
He states, “Other major evolutionary changes in animal form may also be viewed as alterations in the relative growth rates of different parts of the body… such restructuring may result from simple changes in gene regulation. The genetic command to grow at a given time, at a given rate, and in a given way is easily stifled or modified, and the result may be dramatic.” (Pg. 129-130)
He concludes, “If major, genetically coded shifts of adaptation are restricted to speciation by way of small populations, then I would venture a prediction. Humans will perhaps evolve significantly in a biological sense only if they escape this planet for parts unknown. If we are to speciate, it will probably be in space, where small, inbreeding populations may someday colonize new worlds.” (Pg. 207)
This book will be of great interest to those studying evolutionary theory.
Paleontologist and evolutionary biologist Steven Stanley wrote in the Preface to this 1981 book, “What I describe in this book is evidence that evolution is not quite what nearly all of us thought it to be a decade of two ago. This evidence comes largely from the record of fossils---a record that until recently was not well scaled against absolute time. The record now reveals that species typically survive for a hundred thousand generations, or even a million or more, without evolving very much. We seem forced to conclude that most evolution takes place rapidly, when species come into being by the evolutionary divergence of small populations from parent species. After their origins, most species undergo little evolution before becoming extinct. It is only fair to point out that, while this ‘punctuational’ view has displaced the traditional ‘gradualistic’ view in the minds of many evolutionists, there remain dissenters… This book is not designed to build a rigorous case for the punctuational model of evolution---the goal of my more technical volume, ‘Macroevolution’ Pattern and Process.’ Rather, in the present book I attempt to give the interested non-specialist access to the punctuational view and its implications… I also explore the history of the traditional, gradualistic view. Among the most fundamental questions here is why Charles Darwin was a gradualist.” (Pg. xv)
He states in Chapter 1, “human evolution has apparently followed a stepwise course, with important biological change occurring as one species has branched rapidly from another. The fossil record of horses also testifies to an episodic tempo for evolution, and this is particularly notable because for decades the record of ancient horses was heralded as the classic illustration of gradual transformation… Although this fossil record, like all others, is incomplete, so that it fails to document the full history of the horse family, one of its striking revelations is great evolutionary stability for tiny dawn horses… Horses of the modern Equus type obviously evolved rapidly, and apparently for this reason their origin is not documented by known fossil evidence.” (Pg. 4-5)
He continues, “Thus, the new message offered by ancient remains … is that evolution has occurred episodically. Most change has taken place so rapidly and in such confined geographic areas that it is simply not documented by our imperfect fossil record. The resulting view of evolution has become known as the punctuational model, while the contrasting traditional view has been labeled the gradualistic model… The punctuational view implies… that evolution is often ineffective at perfecting the adaptations of animals and plants; that there is no real ecological balance of nature; that most large-scale evolutionary trends are not produced by the gradual reshaping of established species, but are the net result of many rapid steps of evolution, not all of which have moved in the same direction…” (Pg. 5)
He recounts, “What, above all else, has led me to adopt the punctuational view of evolution is the simple observation that chronospecies---lineage segments that embrace little total evolutionary change---last for remarkably long intervals of geological time. In other words, it takes a very long time for a species, once established, to evolve enough to deserve a new name. On the other hand, dramatically new forms of life (species so novel as to require recognition as new genera and families, for example) spring up quite suddenly on a geological scale of time.” (Pg. 15)
He explains, “Darwin capitalized on the fact that the alteration of stages of development often comes late in the history of an embryo, when the animal is approaching the time when it will have to assume its specialized behavior in the outside world…. It was easy for Darwin to see how evolution might have left the earliest stages almost unchanged. On the other hand, why would a creating divinity force all vertebrate beings through the same series of shapes before allowing them to diverge and assume the shapes associated with their postnatal habits?” (Pg. 38)
He continues, "Darwin also cited as evidence structures that we would now term ‘vestigial.’ These are rudiments that seem to serve no present function but that resemble more fully developed, functioning organs in other animals. Some examples are striking. The poorly developed pelvic bones and hind limbs of certain snakes do not fit the animal’s basic body plan, but can easily be accounted for as vestiges of ancestral organs not yet fully lost through evolution… How, Darwin reasoned, could any creator of a perfect global system have been so wasteful or imprecise in his production?” (Pg. 38)
He goes on, “Darwin … remained saddled with the contemporary concept of blending inheritance. This meant that in his day discrete units of genetic inheritance were unrecognized… Given a false belief in blending inheritance, it becomes difficult to imagine how even valuable new adaptations can come to prevail; with every breeding they will be averaged with others. How could selection possibly overcome such dilution instead of becoming blended into oblivion? Darwin… was deeply disillusioned by his inability to extricate his theory from this problem. He could have escaped by focusing on evolution within very small populations isolated by geographic or reproductive barriers… unfortunately, Darwin apparently overlooked this crucial point.” (Pg. 50-51)
He reports of a test he conducted: “I have called the test outlines the test of living fossils… I have tried to include in the test all narrow branches for which we have a fairly good fossil record. The critical point is this: I have yet to uncover one of these that displays marked evolutionary change. Living fossils have represented a thorny puzzle in the traditional, gradualistic scheme of evolution. If natural selection is constantly reshaping species in significant ways, why have some species been almost immune to the process?... These conflicting conjectures on ecological breadth illustrate the dilemma in which gradualism has been trapped by living fossils… The punctuational model provides us with the explanation… The punctuational model … predicts that even the persistent small groups will tend to exhibit little evolution because, however long they may have existed, they have undergone little speciation---and speciation is where most evolution occurs.” (Pg. 85-86)
He observes, “We know that after the demise of the dinosaurs the world was available for occupancy by mammals. Nonetheless, why should mere ecological opportunity cause any well-established species to abandon its way of life for an entirely new one?... Expanded ecological opportunity would be expected to produce great diversification… diversification proceeds by the sprouting off of new species from already established species---by adaptive radiation---and this, of course, brings us to the punctuational scheme of evolution… The new evidence for the stability of early Cenozoic species forces us to focus upon change by speciation involving small populations. Quantum speciation becomes our logical solution to the problem of the great mammalian radiation.” (Pg. 94-96)
He reiterates, “Example after example strengthens the case that rapid evolution is restricted to small populations. For large populations of the sort that constitute the species living all around us today, sluggish change is the norm---much more sluggish change than all but a few modern biologists have envisioned.” (Pg 101)
He points out, “Unfortunately, circular reasoning crept into the evaluation of the [fossil] record. Darwin made elaborate claims that fossil data were too sparse ever to support his gradualistic scheme, yet his condemnation of the record was not based on objective observation. About this, he was quite open in the ‘Origin’… ‘I do not pretend that I should ever have suspected how poor a record of the mutations of life… had not the difficulty of our not discovering innumerable transitional links between the species which appeared at the commencement and close of each formation, pressed so hardly on my theory.’ In other words, Dargin had deduced the incomplete nature of the fossil record from his theory.” (Pg. 105)
He comments about cichlid fishes in Lake Victoria: “Here we have a strong hint of what is important for the occurrence of quantum speciation: ecological opportunity. Given an opportunity like that of the cichlid fishes… most groups of animals or plants would diversify rapidly, yet some groups … display a tendency to undergo particularly spectacular radiations with great frequency.” (Pg. 119)
He states, “Other major evolutionary changes in animal form may also be viewed as alterations in the relative growth rates of different parts of the body… such restructuring may result from simple changes in gene regulation. The genetic command to grow at a given time, at a given rate, and in a given way is easily stifled or modified, and the result may be dramatic.” (Pg. 129-130)
He concludes, “If major, genetically coded shifts of adaptation are restricted to speciation by way of small populations, then I would venture a prediction. Humans will perhaps evolve significantly in a biological sense only if they escape this planet for parts unknown. If we are to speciate, it will probably be in space, where small, inbreeding populations may someday colonize new worlds.” (Pg. 207)
This book will be of great interest to those studying evolutionary theory.
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