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This volume is the result of a NATO Advanced Study Institute held in England at Kingswood Hall of Residence, Royal Holloway College (London University), Surrey, during the last two weeks of July, 1976. The ASI was organized within the guide lines laid down by the Scientific Affairs Division of the North Atlantic Treaty Organization. During the past two decades, significant advances have been made in our understanding of vertebrate evolution. The purpose of the Institute was to present the current status of our know­ ledge of vertebrate evolution above the species level. Since the subject matter was obviously too broad to be covered adequately in the limited time available, selected topics, problems, and areas which are applicable to vertebrate zoology as a whole were reviewed. The program was divided into three areas: (1) the theory and methodology of phyletic inference and approaches to the an­ alysis of macroevolutionary trends as applied to vertebrates; (2) the application of these methodological principles and an­ alytical processes to different groups and structures, particular­ ly in anatomy and paleontology; (3) the application of these re­ sults to classification. The basic principles considered in the first area were outlined in lectures covering the problems of character analysis, functional morphology, karyological evidence, biochemical evidence, morphogenesis, and biogeography.

Evolutionary Biology, of which this is the eighteenth volume, con­ tinues to offer its readers a wide range of original articles, reviews, and commentaries on evolution, in the bro~dest sense of that term. The topics of the reviews range from anthropology and behavior to molecular biology and systematics. In recent volumes, a broad spectrum of articles have appeared on such subjects as natural selection among replicating molecules in vitro, mate recognition and the reproductive behavior of Drosophila, molecular systematics ofCrocodilia, evolution of the monocotyledons, and the com­ munication network made possible among even distantly related genera of bacteria by plasmids and other transposable elements. Articles such as these, often too long for standard journals, are the stuff of Evolutionary Biology. The editors continue to solicit manuscripts on an international scale in an effort to see that everyone of the many facets of biological evolution is covered. Manuscripts should be sent to anyone of the following: Max K. Hecht, Department of Biology, Queens College of the City University of New York, Flushing, New York 11367; Bruce Wallace, Department of Biology, Virginia Polytechnic Institute and State University, Blacks­ burg, Virginia 24061; Ghillian T. Prance, New York Botanical Garden, Bronx, New York 10458.

Evolutionary Biology, of which this is the nineteenth volume, continues to offer its readers a wide range of original articles, reviews, and com­ mentaries on evolution, in the broadest sense of that term. The topics of the reviews range from anthropology and behavior to molecular biology and systematics. In recent volumes, a broad spectrum of articles have appeared on such subjects as natural selection among replicating molecules in vitro, mate recognition and the reproductive behavior in Drosophila, evolution of the monocotyledons, species selection, and the communication net­ work made possible among even distantly related genera of bacteria by plasmids and other transposable elements. Articles such as these, often too long for standard journals, are the stuff of Evolutionary Biology. The editors continue to solicit manuscripts on an international scale in an effort to see that everyone of the many facets of biological evolution is covered. Manuscripts should be sent to anyone of the following: Max K. Hecht, Department of Biology, Queens College of the City University of New York, Flushing, New York 11367; Bruce Wallace, Department of Biology, Virginia Polytechnic Institute and State University, Blacks­ burg, Virginia 24061; Ghillian T. Prance, New York Botanical Garden, Bronx, New York 10458. The Editors vII Contents 1. Discontinuous Processes in the Evolution of the Bacterial Genome........................................ 1 Monica Riley Introduction...............................,........ 1 Internal Rearrangements............................... 2 Large-Scale Internal Rearrangements.................... 2 Small-Scale Rearrangements: Divergence of Duplicate Genes......................................... 11 Interactions between Two Genomes...................... 20 Transposons: Jumping Genes.................... 20...... Plasmids: Incorporation into Genomic DNA.............. 23.

Evolutionary Biology, of which this is the twenty-first volume, continues to offer its readers a wide range of original articles, reviews, and com­ mentaries on evolution, in the broadest sense of that term. The topics of the reviews range from anthropology and behavior to molecular biology and systematics. In recent volumes, a broad spectrum of articles have appeared on such subjects as evolution of the bacterial genome, biochemical system­ atics in plants, a discussion of species selection, and development and evolution of the vertebrate limb. Articles such as these, often too long for standard journals, are the material for Evolutionary Biology. The editors continue to solicit manuscripts on an international scale in an effort to see that everyone ofthe many facets of biological evolution is covered. Manuscripts should be sent to anyone of the following: Max K. Hecht, Department of Biology, Queens College of the City University of New York, Flushing, New York 11367; Bruce Wallace, Department of Biology, Virginia Polytechnic Institute and State University, Blacks­ burg, Virginia 24061; or Ghillian T. Prance, New York Botanical Garden, Bronx, New York 10458.

Sixteen volumes and one supplement have now appeared in the series known as Evolutionary Biology. The editors continue to seek critical re­ views, original papers, and commentaries on controversial topics. It is our aim to publish papers primarily of greater length and depth than those normally published by society journals and quarterlies. The editors make every attempt to solicit manuscripts on an international scale and to see that every facet of evolutionary biology-classical or modern-is cov­ ered. Manuscripts should be sent to anyone of the following: Max K. Hecht, Department of Biology, Queens College of the City University of New York, Flushing, New York 11367; Bruce Wallace, Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061; Ghillean T. Prance, New York Botanical Garden, Bronx, New York 10458. The Editors vii Contents 1. Darwinian Selection of Self-Replicating RNA Molecules 1 Christ(~r K. Biehricher Introduction........................................ Replication of Virus RNA in Vitro........................ 2 Extracellular Darwinian Experiments...................... 5 Characterization of the QI3 Replicase...................... 9 Nonviral RNA Templates of QI3 Replicase.................. II The Mechanism of RNA Replication...................... 14 Initiation of Replication and Template Specificity........... 14 Mechanism of Replica Chain Elongation.................. 17 Termination of Replication............................ 19 Replication of RNA Variants.......................... 21 TheQuasispecies..................................... 23 De NOl'O Synthesis of Self-Replicating RNA................. 27 The Mechanism of Selection............................ 32 Selection in the Exponential Growth Phase................ 32 Selection in the Linear Growth Phase.................... 35 Conclusions........................................ 41 Appendix I. Replication................................ 42 Appendix II. The Quasispecies........................... 43 Appendix III. Selection under Various Conditions............ 44 References.........................................

The ninth volume of Evolutionary Biology represents a turning point in the history of this series. The death of Theodosius Dobzhansky was a blow to the whole field of evolutionary biology in general, and to his friends and colleagues, including the other two Editors. He played a central role in the selection of areas that were'ripe'for review papers, and his circle of friends, colleagues, and students was so wide that he could always find exactly the most appropriate author and then convince him that he should prepare the paper. Evolutionary Biology was founded in 1966 and the first volume published in 1967. Ten years-and several vicissitudes-later, it seems advisable to restate the original concept of this serial publication. The Preface of Volume 1 says, simply, We have conceived this serial as a forum in which critical reviews and com­ mentaries, as well as original papers and even controversial views, can be brought together to cover a broad range of interest with provocative discussion. Evolutionary Biology will provide research workers and students with an excep­ tional opportunity to read expert presentations of developments in areas of their field in which they are not specialists, and as specialists they will see how others assess these developments. An important feature is that contributions are not necessarily limited in length, subject, and other restrictions that usually prevail in basic research journals.