Professor Trevor Palmer is Head of the Department of Life Sciences and Dean of the Faculty of Science at the Nottingham Trent University (formerly Polytechnic). He graduated in biochemistry from Cambridge University in 1966 and obtained a PhD from London University in 1973 for research in the field of inborn errors of metabolism. This work stimulated his interest in the origin and evolutionary consequence of genetic mutations. Professor Palmer is a Chartered Biologist and a Fellow of the Institute of Biology. He is the author of Understanding Enzymes (now in its third edition) and Principles of Enzymology for Technological Applications. In addition, he is author/co-author of around 70 research papers and review articles concerned with inborn errors, enzymology or evolution. He has been a member of SIS Council since 1986.
Published in Great Britain in 1994 by the Society for Interdisciplinary Studies in association with The Nottingham Trent University
(c) Copyright Trevor Palmer, 1993
Society for Interdisciplinary Studies ISBN 0 9514307 1 8
Nottingham Trent University ISBN 0 905488 20 2
Fossil (incomplete) of an ammonoid. The Ammonoida, a subclass of the Cephalopoda, became extinct during the Cretaceous-Tertiary transition. (Photograph: Maggie Martin)
Catastrophism, Neocatastrophism and Evolution tells how prevailing views of patterns and processes in the evolution of life on Earth have changed in a significant fashion over the past few years. In 1959, the centenary of the publication of Charles Darwin's On the Origin of Species by means of Natural Selection, the Modern Synthesis of neo-Darwinism, which incorporated developments in genetics into traditional Darwinism, seemed completely secure. Together with the contemporary geological paradigm, the Modern Synthesis was widely seen as representing the triumph of a gradualistic-uniformitarian view of Earth history over the catastrophist alternative. Evolutionary change was slow (an essential feature of gradualism), imperceptible (except over long periods of time) and progressive (though not because of linear development, but as a result of competition between variant forms). Later, however, it became increasingly clear that the course of evolution had been much less even paced and much more erratic than previously realised, the fossil record revealing episodic rapid bursts and abrupt transitions, which could no longer (as formerly) be dismissed as artifacts. Moreover, from 1980 onwards, neocatastrophism made remarkable advances so that, today, impacts of asteroids and comets have to be regarded as perfectly plausible agents of evolutionary change, and evidence for such an extraterrestrial involvement at any particular time considered on its merits.
Something of a revolution in academic thought has taken place, but as with other paradigm shifts in the scientific world, there are those who deny that it has happened. As Archie Roy, Professor of Astronomy at Glasgow University, said at an SIS meeting in London in 1985, it is not unknown for the response to a new idea to progress from "This man is nuts", through "We'll really have to look at the problem just to dismiss it", to "Of course I've always known that this was the case". With the subject of evolutionary biology, which is our particular concern, the imprecise and subjective nature of some of the terminology makes it possible for those who wish to do so to maintain that the essentials of the gradualistic viewpoint remain intact. For example, a significant evolutionary change taking place over several thousand years (rather than several hundred thousand years) might be cited by some as an example of a rapid transition, whilst others would have no difficulty in accepting it as falling within the range that could be regarded as gradualistic. Hence, one of the aims of the present work is to go beyond assertions and give the full flavour of views about contemporary and historical evolutionary theory which have received wide circulation in books and general science journals such as Nature, Science, Scientific American and New Scientist. The change in tone of such writings over the years is very apparent, leaving little scope for misrepresentation. Nevertheless, in order to convey opinions and arguments with maximum accuracy, extensive quotations are given. In the light of these, it should be evident that a major change of perspective, if not a revolution, has occurred over the past decade or so.
Chapter 1 of Catastrophism, Neocatastrophism and Evolution serves as an introduction. It shows that catastrophic events in the form of collisions between cosmic bodies have occurred throughout the history of the Solar System; the Earth has suffered many impacts, most of them small, but some large enough to have caused widespread devastation, and today Earth is still threatened by orbit-crossing asteroids and comets. As we shall see, ignorance of this extraterrestrial dimension by nineteenth century catastrophists and uniformitarians alike contributed to the demise of catastrophism, and increasing knowledge of it in more recent years has stimulated the rise of neocatastrophism. Regardless of that, it is beyond question that mainstream scientists throughout most of the twentieth century considered catastrophism to be dead.
Chapter 2 looks at the nature of catastrophism in previous times, and the reasons for its apparent defeat by uniformitarianism in the nineteenth century. Uniformitarianism was formulated by Charles Lyell in a geological context, but its principles and attitudes were adopted by Charles Darwin for his theory of evolution, subsequently developed into the Modern Synthesis. There was a general belief that catastrophism and evolution were alternative, mutually exclusive, explanations for the fossil record and, as fossil evidence accumulated during the second half of the nineteenth century, it became increasingly clear that the features observed could not be explained by the Earth-centred model of catastrophism then in vogue, which linked extinctions of species to crustal upheavals on a global scale.
Also, Lyell had deliberately caused confusion by giving two different meanings to uniformitarianism. Actualistic uniformitarianism, the principle that physical processes operate according to unchanging laws, was widely acclaimed by scientists of all persuasions, then and subsequently. In contrast, substantive uniformitarianism, the belief that human beings had been around long enough by Lyell's time to know that the Earth's present state was typical of its entire history, has received far less acclaim. Indeed, there seems to be no justification for excluding the possibility that major events caused by processes operating in accordance with unchanging natural laws should not occur in an episodic fashion, widely separated in time. Nevertheless, an unnecessary association was established between actualistic and substantive uniformitarianism and, since no global catastrophes had apparently been observed in historical times, uniformitarianism came to imply gradualism, this being stretched to include minor catastrophist elements such as earthquakes and volcanic eruptions. Then, as a result of distortions propagated by Lyell and others, subsequent generations were led to believe that the views of the catastrophists owed more to pre-conceived ideas than to observation, whereas the theories of the uniformitarians were all derived by logical deduction from observed data. At best this was over-simplistic, at worst a reversal of the truth, yet the myth became widely accepted. It also became received opinion, quite falsely, that the catastrophists relied on supernatural explanations for the cause of the major catastrophic events which had supposedly taken place. It is true that they refused to rule out the possibility of fresh creations of life at intervals throughout Earth history, but Lyell took exactly the same line himself after his formulation of uniformitarianism, before he became an evolutionist in his old age. With the demolition of the myth that the nineteenth century catastrophists were driven by religious dogma, there remains no reason for having to distinguish between catastrophism and neocatastrophism in the twentieth century.
Chapter 3 is concerned with challenges to evolutionary gradualism up to the year 1980. Many of these challenges involved attempts to introduce extraterrestrial models of catastrophism. However, there had always been resistance to suggestions that the Earth might be subject to interference by external factors. So, for example, when the great French chemist, Antoine Laurent Lavoisier, acting on behalf of the Académie des Sciences, investigated an incident in which a large stone was reported to have fallen from the sky near Luce in 1768, he concluded that nothing of the sort could have happened, and therefore all the witnesses must have been either mistaken or lying. However, a whole shower of meteorites landed in 1803, giving the new investigator, Jean Baptiste Biot, no option but to accept their extraterrestrial origin. Nevertheless, when Thomas Jefferson, President of the USA, who included palaeontology amongst his many interests, was told in 1807 that two Yale scientists were claiming that meteorites had recently struck the Earth at Weston, Connecticut, he is reported to have replied, "It is easier to believe that two Yankee Professors would lie, than that stones would fall from Heaven". In spite of prejudice such as this, the extraterrestrial origin of meteorites was well established by the start of the twentieth century, but not until the 1960s did it become generally accepted that impacts had caused many of the large craters found on the Earth's surface, and the arguments of M. W. Laubenfels, René Gallant, Harold Urey, Digby McLaren and others that such impacts could have influenced the evolution of life fell on deaf ears, even though episodes of mass extinction were evident from the fossil record.
Similarly, Otto Schindewolf's hypothesis that a supernova explosion could have been the cause of mass extinction events was largely ignored, whilst his view (and that of Richard Goldschmidt) that macromutations might account for the origin of new species provoked derision. Abuse was also poured on Immanuel Velikovsky for his theory that the Earth had suffered several major catastrophes as a result of coming into close contact with planetary-sized cosmic bodies.
Norman Newell did much to establish that mass extinctions were real events, but he favoured gradualistic explanations for their cause. This line was generally followed by evolutionary biologists, developing theories involving plate tectonics and continental drift. However, during the 1970s, the strictly gradualistic view of evolution came under challenge from within the Modern Synthesis by Stephen Jay Gould, Niles Eldredge and Steven Stanley, who argued that, according to the fossil record, evolutionary change tended to occur in rapid bursts separated by periods of stasis. Moreover, overall evolutionary trends were not necessarily determined by the gradual accumulation of small modifications.
Chapter 4 deals with the dramatic changes in attitude towards catastrophism since 1980, stimulated by the hypothesis of Luis Alvarez and colleagues that high iridium concentrations found at the Cretaceous-Tertiary boundary throughout the world could be taken as evidence that the mass extinction episode at the end of the Cretaceous Period had been caused by the impact of a large asteroid. Further evidence for this has come in the form of microtektites, pollen grains, soot, shocked quartz grains, rippled sandstone, stishovite, amino acids and diamonds. However, the iridium abundance anomaly, together with some of the other features, could also have been the result of extensive vulcanism, which is known to have occurred at this time. Vulcanism on this scale has to be regarded as a catastrophist mechanism so, throughout much of the past decade, the arguments have been about which of two catastrophist mechanisms, one terrestrial, the other extraterrestrial, played a major role in events at the Cretaceous-Tertiary boundary. Furthermore, it is possible that both were involved, the widespread vulcanism being a direct consequence of the impact of a large bolide. What appears to be an enormous impact structure with an appropriate age has been located at Chicxulub, in Mexico. However, the detailed evidence collected over the years indicates that the Cretaceous-Tertiary extinctions were far from instantaneous, suggesting that a mixture of catastrophist and gradualistic factors, or possibly a succession of impacts, perhaps from a shower of comets, might have been responsible.
Similarly at other mass extinction horizons, there is evidence that, to a greater or lesser extent, both catastrophist and gradualistic mechanisms, including continental drift, might have played significant roles. The suggestion has been made that there is a periodicity in mass extinctions, and various mechanisms have been proposed which could bring a cluster of comets into the inner Solar System at regular intervals, but none of these has found general acceptance. Nevertheless, one thing that is now firmly established is that the extinction of the dinosaurs at the end of the Cretaceous Period cleared the way for the emergence of mammals, and eventually of ourselves.
Chapter 5 looks in detail at the evolution of humankind, and finds that it was an erratic and unpredictable process. Although `molecular clocks' do not keep perfect time, their development has stimulated a re-assessment of fossil evidence, and it is now clear that the human (hominid) line split off from the ape line much later than had been thought. In the subsequent evolution towards Homo sapiens, several different hominid species have been identified, but the precise number of species, and the relationship between them, remains a matter for argument. It is still uncertain whether all present day humans are descended from a single population which lived in Africa (or perhaps Asia) in relatively recent times, or whether parallel evolution has occurred in different parts of the world.
Another controversial issue is whether the characteristics of each hominid species changed significantly with time. However, it is generally agreed that new species appeared in a rapid fashion, and the disappearance of species was also quite abrupt. This whole process took place against a background of major environmental changes. To some extent these can be explained by continental drift, but catastrophist mechanisms may also have been involved.
Chapter 6 asks, in the light of all of this, where evolutionary theory stands today. Modern developments in molecular genetics have provided no support for Lamarckism, since they have not revealed any mechanism by which specific genetic changes could be produced in direct response to environmental pressures. On the other hand, the observed genetic processes were consistent with neo-Darwinism, which maintains that variations arise by factors which are not directly related to environmental pressures, natural selection then determining which variants are most successful in passing their genes on to subsequent generations. Nevertheless, confusion arose because the word `random' was widely used as a shorthand for `not directly related to environmental pressures', and it became increasingly obvious that the production of variants was not random in the true sense of the word, possibly involving laws and levels of organisation still to be discovered. Similarly, the relationship between evolution at different levels, from molecules to species and above, needs to be clarified. Thus the Modern Synthesis, if not actually wrong, is far from complete.
In any case, when species diversity is high, it is likely that natural selection acts mainly as a stabilising factor, rather than driving evolution forward. However, when species diversity is low and many ecological niches are vacant, as in the aftermath of a mass extinction, there are much greater opportunities for new variants to become established, and to give rise to further variants. For this reason, mass extinctions, whether resulting from catastrophist or gradualistic mechanisms, or a combination of the two, have had a highly significant bearing on the course of evolution. The characteristic pattern of evolution is of extinctions followed after a pause by the rapid radiation of new species into vacant ecological space. This picture is very different from that envisaged by the founders of the Modern Synthesis: these took the lead from Darwin himself, who wrote in The Origin of evolution proceeding `slowly and progressively ... like the branching of a great tree from a single stem', with extinct species simply being compared to branches which had `decayed and dropped off'.
Some of the material used in Catastrophism, Neocatastrophism and Evolution has appeared before, in the form of review articles or shorter pieces in the SIS publications, Review and Workshop. The titles of chapters 4, 5 and 6 have been taken from three such review articles, which were published in the period 1988-1990. However, most of the material is new, whilst the rest has been updated and re-written to fit into the scheme of the present work. The outline of the argument is essentially that followed in a paper entitled `Catastrophism and Evolution', which was presented at an SIS meeting in Nottingham in 1983 and published in the Review in 1985. A great deal of new evidence has been produced since then, but the general conclusions reached in that paper about overall patterns and mechanisms in evolution, with extraterrestrial impacts being possible causal agents of mass extinctions, and with radiations of new species generally following mass extinctions, rather than being contributory causes of them, remain valid today. Indeed, they now have a much more solid foundation, and would receive much wider support than previously. Now that the developments of the 1980s are being consolidated, it seems an appropriate time to present them in some detail, and place them in their historical context. That is what Catastrophism, Neocatastrophism and Evolution has attempted to do.
This work would not have been possible without the help or inspiration of far more people than I can name. To start with, I am grateful to my colleagues at Nottingham Trent University, especially Graham Compton, David Godden, Neal Priestland and Clive Williams for discussions on some of the topics covered by this book; to Angela Adcock, Pauline Polkey and Sharon Morrison for secretarial assistance; and to the library staff of the University for their co-operation in obtaining copies of many papers.
Amongst the public speakers who have stimulated my thoughts (although not necessarily bringing me to agree with their views) have been Victor Clube, David Rohl, Archie Roy, Rupert Sheldrake, Peter Warlow and Chandra Wickramasinghe at SIS meetings, and Guy Bush at the Linnean Society.
Even more writers of books and articles (by a considerable margin, in numerical terms) have provided me with new knowledge and fresh perspectives. It would perhaps be invidious to single out any authors for special mention, even ones such as Stephen Jay Gould, Niles Eldredge, Steven Stanley and David Raup (amongst those still active), whose writings have given me many hours of pleasure and rewarding study - for where does one draw the line? Nevertheless, in varying degrees I am grateful to them all, including those whose arguments I found less than convincing, thus stimulating the formulation of counter-arguments.
I must thank Peter James and Brian Moore for first encouraging me to write on evolutionary topics for SIS publications and all members of Council for subsequent encouragement. Similarly, I must express my gratitude to my wife Jan, son James and daughter Caroline for putting up with piles of books and papers around the house, not to mention the seemingly endless hours I have spent at the word processor.
Amongst current and former members of SIS Council, special thanks are due to Jill Abery, Eric Crew, Bernard Newgrosh and David Salkeld for critical discussions which have helped to sharpen up some of my ideas, and how to express them. I am also grateful to Jill for her help with some of the figures and, most particularly, to Bernard for his excellent editorial work.
However, I must make it clear that all the views expressed in Catastrophism, Neocatastrophism and Evolution (except where attribution is given) are my own and I take full responsibility for any errors. For me at least, writing is never a pleasurable activity for, no matter how certain I think I am about what I want to say, the precise sequence of words required to bring this about invariably proves elusive and comes, if at all, after much time and effort. Nevertheless, if in the following pages I can convey to the reader something of the excitement I have experienced in following developments concerning catastrophism, neocatastrophism and evolution over the past 15 years, then the effort involved will have been very worthwhile.