I have so many things to write about, that my head is as full of oddly assorted ideas, as a bottle on the table is filled with animals.
- Charles Darwin, 1832, Rio de Janeiro
Evolutionary biology enjoys the peculiar dual status of being that subject which clearly unites all biological endeavors, while occasionally seeming to be nearly as remote from complete understanding as when Darwin brought it within the realm of materialistic science. Somehow, the basic precepts first proposed by Darwin have never been either fully accepted or disposed, to be followed by a movement toward further progress in some other direction. The arguments of today - the questions of natural selection and adaptation, saltation versus gradualism, and questions of relatedness among organisms - are not all that different from those discussed 100 years ago, even if the research materials seem that much more sophisticated.
Darwin espoused thinking in terms of populations. His approach was open to experimentation, but this had to await the (re)discovery of genetics half a century later, before a major impediment to our understanding could be thrown aside. As it turned out, the rediscovery of genetics was initially more confusing than helpful to our understanding of evolution. The rediscovery of genetically transmissible discrete traits revived saltationism, and it took over a decade for biologists to realize that there was no conflict between the origin of discrete variants and the theory of natural selection. In the twentieth century, the focus of experimentalists moved toward processes occurring within populations. But many of the inherently most fascinating questions lie at higher taxonomic levels, or at greater distances of relationship than between individuals in a population. The questions are both descriptive and mechanistic. We would like to know just how to describe the difference between a lizard and an elephant, in terms that would make it possible to conceive of the evolutionary links between them. We are only now beginning to do this, principally at the molecular genetic level. Differences in nucleotide sequences are beginning to have more meaning at this level, especially because of the emerging knowledge of gene regulation. But we would also like to understand the mechanisms behind the evolutionary process at higher levels of morphological organization. This inevitably involves a knowledge of history with all the limitations that that subject embraces. Just how can we be sure about biological historical facts? Surely the fossil record must come into play here, even if it is scattered in preservation.
I will try here to provide an approach to studying macroevolution, which I define to be the study of transitions between related groups of distant taxonomic rank. The formula is simple. First, we must have a sound systematic base that is derived from a well-established network of genealogical relationships. Otherwise, we cannot ask the appropriate questions in the first place. Second, we must be able to describe the differences between organisms in molecular, developmental, morphological, and genetic terms. Third, we must understand the processes of evolution at all levels, from the nature of polymorphisms to the appearance and extinction of major groups. Finally, we must have a criterion by which adaptation can be judged. It may not be true that one group is inherently superior to another unrelated group. But if we cannot devise a criterion for increases in performance, even in biologically complex organisms, then we will not be able to test Darwin's claim that evolution involves improvement (not perfection) in a given context of an organism-environment relationship.
Because the problems require such a broad scope of approaches and solutions, our understanding of macroevolution is often mired in arguments that appear, then disappear, then reappear, with no real sense of progress. The saltationist-gradualist argument has had such a history, simply because of our lack of knowledge as to what saltation really means and the usual lack of a good historical record. Because evolutionary biologists tend to reason by example, it is easy to "prove a point" by citing a hopelessly obscure case or one that may turn out to be unusual. Yet it seems fruitless to settle an argument by counting up all of the examples to prove a claim, without some theoretical reason to expect the majority of cases to fit in the first place. This danger is endemic to a science that depends on history. Most biologists would be quite disappointed if evolutionary biology were nothing much more than a form of stamp collecting. We look for theories and principles.
It is my hope that this volume will provide a framework within which to view macroevolution. I don't pretend to solve the important issues, but I do hope to redirect graduate students and colleagues toward some fruitful directions of thought. Although I like to think that this is a balanced presentation, my shortcomings and prejudices will often surface. In particular, this volume will resort to advocacy when attacking the view of evolution that speciation is a fundamental level of evolutionary change in the macroevolutionary perspective, and that the neo-Darwinian movement and the Modern Synthesis somehow undermined our ability to understand the process of evolution and brought us to our present pass of misunderstanding. The recent "born again" moves toward saltationism, and the staunchly ideological adherence to related restrictive concepts, such as punctuated equilibria, are great leaps backward and have already led many toward unproductive dead ends that are more filled with rhetoric than scientific progress. Ultimately this is a pity, because some of these ideas have been interesting and have exposed unresolved issues in evolutionary theory.
Although this book is principally meant to be a blueprint for the study of macroevolution, I found it necessary to discuss certain areas at an elementary level.
This is partially owing to the heterogeneous audience that I anticipate. I doubt that most paleontologists will be aware of the details of genetics, and neontologists will similarly benefit from some geological introduction.
Many colleagues were very generous with their time in reviewing this manuscript. I thank the following who reviewed one or more chapters: Richard K. Bambach (chapters 1-8), Michael J. Bell (chapters 3, 4, 7), Stefan Bengtson (chapters 7, 8), John T. Bonner (chapters 1-8), Peter W. Bretsky, Jr. (chapters 7, 8), Brian Charlesworth (chapters 3, 7, 8), John Cisne (chapter 7), Richard Cowan (chapters 6, 7), Gabriel Dover (part of chapter 3), Walter Eanes (chapters 3, 4), Joseph Felsenstein (chapter 2), Karl Flessa (chapter 8), Douglas Futuyma (chapters 1, 3, 4), Paul Harvey (part of chapter 6), Max Hecht (chapters 1-8), George Lauder (chapter 6), Jack Sepkoski (chapter 8), David Wake (chapter 5), and especially David Jablonski (chapters 1-9). This sounds like extensive reviewing, but consider my extensive ignorance.
I also have been lucky to have had conversations or correspondence with many individuals who gave me useful information, their unpublished works, letters, insights, and important references. Among them, I am grateful to Bill Atchley, David Wake, Björn Kurten, Lars Werdelin, Steve Orzack, John Maynard Smith, Brian Charlesworth, Michael Bell, Pete Bretsky, Gabriel Dover, Steve Farris, Steve Stanley, Doug Futuyma, Walter Eanes, Curt Teichert, George Oster, Richard Reyment, Jürgen Schöbel, Max Hecht, Russell Lande, Art Boucot, Ledyard Stebbins, Vjaldar Jaanusson, Ernst Mayr, George Gaylord Simpson, Jack Sepkoski, and Urjö Haila.
The manuscript for this book was prepared using the Document Composition Facility at the Biological Science Computing Facility at the State University of New York at Stony Brook. I am very grateful to Dave Van Voorhees, who, in the main, formatted the manuscript into appropriate files. Scott Ferson, Kent Fiala, and Jim Rohlf were infinitely patient with our questions, and all contributed materially to our ability to produce the final product. I am also very grateful to Mitzi Eisel and to Marie Gladwish for skillfully preparing most of the figures. I also thank Richard Ziemacki, Helen Wheeler, Jim DeMartino, Peter-John Leone, and especially Rhona Johnson, all of Cambridge University Press, for their patience and kindness. Most of all I am grateful to my wife Joan, who made life so easy (at least for me) while I prepared the manuscript.
I am very grateful for the hospitality of Staffan Ulfstrand, Zoology Department of the University of Uppsala; Gabriel Dover of the Department of Genetics at Kings College, University of Cambridge; Catherin Thiriot, Odile Mayzaud, and Patrick Mayzaud, all of the Station Zoologique, Villefranche-Sur-Mer, France; and Jacques Soyer, Laboratoire Arago, Banyuls-Sur-Mer, France. I also am deeply grateful to the Guggenheim Foundation, which mainly supported the writing of this work.
Banyuls-Sur-Mer and Stony Brook
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