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Origins of Sex

Origins of Sex: Three Billion Years of Genetic Recombination

Copyright Date: 1986
Published by: Yale University Press
Pages: 259
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  • Book Info
    Origins of Sex
    Book Description:

    A fascinating and detailed examination of the evolution-and occasional devolution-of sexuality in microorganisms and more complex forms of life. Margulis and Sagan trace sex from its inauspicious beginnings in bacteria threatened by ultraviolet radiation to its intimate relation with the origin of mitotic division of nucleated cells. The origin of meiotic sex through cannibalism followed by centriole reproductive tardiness and the connection of cell symbiosis to sex and differentiation are explored."The authors have not only given us a new and exiting scenario for the evolution of sex, but have also provided us with critical ways in which we can test their hypotheses. . . . This is a stimulating book that is sure to invoke criticism and discussion; I strongly recommend it."-Symbiosis"The book is well organized and well written, leading the reader from one thought to another almost effortlessly. Background information is presented to aid those of us who are not experts in this field, and a glossary is appended. The book could be used at all levels of study, from interested undergraduates in general biology though postdoctoral students of genetics and evolution. I recommend this thought-provoking book to you for both your enjoyment and your enlightenment."-Richard W. Cheney, Jr.,Journal of College Science Teaching"This book, undoubtedly controversial, is a thoughtful and original contribution to an important aspect of cellular biology."-John Langridge

    eISBN: 978-0-300-16098-7
    Subjects: Ecology & Evolutionary Biology

Table of Contents

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  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-viii)
  3. List of Figures
    (pp. ix-x)
  4. List of Tables
    (pp. xi-xii)
    (pp. xiii-xiv)
    (pp. xv-xx)
  7. INTRODUCTION For Whom This Book Is Meant
    (pp. 1-8)

    This book is meant to be an evolutionary detective story that unravels the mystery and history of the origin of sex. Different forms of sex are observed in the biological world. We want to know how sex came to be.

    Sex in bacteria crosses species boundaries and allows a flow of genetic information that some consider the basis for a worldwide gene pool composed of bacteria (Sonea and Panisset, 1983). Other organisms, those with nuclei, probably evolved through endosymbiosis: bacteria living inside each other shared each other’s foods, metabolites, and eventually genes (Margulis, 1981). Nonbacterial, meiotic sex, found only in...

  8. 1 WHAT IS LIFE? DNA, Autopoiesis, and the Reproductive Imperative
    (pp. 9-15)

    To understand sex and its origins we must first know about some fundamental properties of life: autopoiesis (self-maintenance), growth, and reproduction. These three defining properties of all life are visible manifestations of a detailed carbon chemistry—and all three are likely to occur in a total absence of sex. Through an immense stretch of evolutionary time—the first three billion years of life—sex was usually not required for self-maintenance, growth, or reproduction. Bysexwe mean a process characteristic of live organisms only: the complex set of phenomena that produces a genetically new individual, an individual that contains genes...

  9. 2 WHAT IS EVOLUTION? Cell DNA Continuity and the Necessity of Error
    (pp. 16-24)

    This book attempts to tell the story of the evolution of sex. But before we can discuss the relationship between sexuality and evolution we must know, in biochemical terms, what evolution really is. To know that, we must first know what reproduction is, because it is only throughdifferential reproduction—the reproduction of some organisms more than others—that evolution, or changes in populations over time, can occur. Ultimately, all acts of reproduction, from bacterial parasites bursting from their host cells to the birth of a human infant, are based on the replicative ability of DNA.

    Understanding, in chemical detail,...

  10. 3 WHAT IS SEX? Molecular, Cellular, and Organismal Recombinations and Fusions
    (pp. 25-37)

    Whereas sexual processes must involve the production of genetically new individuals, they do not require an increase in the total number of individuals. Reproduction, on the other hand, invariably results in an increase in the number of live beings. The minimal number of individuals before an act of reproduction is one; the minimal number afterward is two. One individual may, in a single act of reproduction, form only one more individual. This is the usual case when a bacterium or an amoeba divides. A single individual, in other instances, may form up to several hundred offspring in one reproductive event—...

  11. 4 THREATS TO DNA AND THE EMERGENCE OF SEXUALITY Ultraviolet Light, Chemical Death, and DNA Repair
    (pp. 38-53)

    Our narrative history of sexuality from now on will follow, insofar as possible, the chronology of life on Earth. Cosmologists, nuclear physicists, astronomers, and space scientists have colossally changed many of the most basic human beliefs. Working independently, they have produced myriads of diverse data for investigative minds to sort out and integrate. We slowly build a picture of the timescape (Calder, 1983). In the most prevalent model, the universe, forming in the biggest bang imaginable, came into being in about three minutes 13,500 million years ago (Weinberg, 1977), and it has been expanding ever since. In about a second...

  12. 5 RECOMBINATION AND BACTERIAL MATING Worldwide Evolutionary Changes through Microbial Sex
    (pp. 54-61)

    Whether most bacteria are capable of mating is not known; neither is the extent of bacterial conjugation in nature (Sonea and Panisset, 1983). Some bacteria mate with enough consistency, however, that the process can be studied in the laboratory. In bacterial mating, or bacterial conjugation, two cells must first come into physical contact so that their outer membranes touch (fig. 15; see also fig. 7).

    The mating is always polarized, never reciprocal: one mate donates genes to the other mate. The donor is conceptually the “male,” because the genes travel from “him” to be received by “his” partner, conceptually a...

  13. 6 THE EMERGENCE OF PROTISTS Symbiotic Bacteria and Organellar Sex
    (pp. 62-113)

    Present-day members of the kingdom Protoctista are as diverse as and more numerous than members of the kingdom Animalia or Plantae. Yet our knowledge of protoctists is still in its infancy. Nonetheless, a study of protoctists, and especially of the unicellular protoctists, by definition protists, is indispensable to an understanding of the origin of meiotic sex. The protists undergo more varieties of meiotic sex than any other kind of organism. All are capable of single-parent, asexual reproduction. In addition to the asexuality standard in this group, some protists have two-parent sexuality in their life cycle. Some divide mitotically, just like...

  14. 7 THE ORIGIN OF CHROMOSOMES Packaging of Chromatin
    (pp. 114-123)

    In this chapter we will look at the specific structural differences of DNA organization between bacteria and meiotic eukaryotes. By examining unique organisms such as the dinomastigotes, which exhibit structural features of both, it will be possible to trace the path from direct bacterial cell division to mitosis. The expanding armamentarium of tools developed by molecular biologists permit us far more precision in our evolutionary analyses than ever before.

    There are many differences between the organization of the prokaryotic genome, or genophore, and the genomic organization of eukaryotes. To understand the emergence of meiotic sexuality, the properties of its prerequisite,...

  15. 8 CHROMOSOME DEPLOYMENT IN MITOSIS Microtubules and Their Organizing Centers
    (pp. 124-145)

    The mitotic apparatus consists at least of the mitotic spindle and often of other microtubular structures such as asters and centrioles as well (fig. 29). Visible in many cells during mitotic division, it is entirely responsible for the movement (called “segregation”) of offspring chromatin to the poles of dividing cells, that is, to the incipient offspring cells (fig. 30). In this way mitosis ensures the orderly distribution of at least one set of genes to each offspring cell. Since the absence of genes or their presence in irregular numbers is lethal, the mitotic apparatus is indispensable to cells that divide...

  16. 9 CANNIBALISM AND OTHER MERGERS Protistan Dilemma of Doubleness
    (pp. 146-152)

    Meiotic sex encompasses the halving and doubling of the number of chromosomes. The doubling of chromosomes, into what is known as the diploid state of two sets of chromosomes, begins with fertilization. In this chapter we explore the possibility that protists originally cannibalized other protists but did not digest them. This would have doubled the number of chromosomes without the fertilization that later became an established part of the life cycle of some eukaryotes.

    In the last century August Weismann developed the concept of “ploidy,” referring to the number of sets of chromosomes in a plant or animal cell. (The...

  17. 10 PAIRING AND HALVING Fertilization and Meiosis
    (pp. 153-169)

    Only diploid, tetraploid, or other even-number ploidy cells can divide by meiosis and survive. A diploid cell that divides by meiosis produces haploid cells, a tetraploid cell produces diploid cells. Any other known cell dividing by meiosis produces aneuploid offspring lacking a complete set of chromosomes and will tend to die. Diploidy is favored in the origin of meiosis because tetraploidy and other higher ploidies are more complex. More can go wrong and thus they are more prone to elimination by selection. Meiosis in many mastigotes and perhaps in the dinomastigoteCryptothecodiniumoccurs in only a single cell division that...

  18. 11 MEIOSIS AND CELL DIFFERENTIATION From Microbial Community Ecology to Endocytobiology
    (pp. 170-182)

    A central thesis of this book is that the eukaryotic cell is homologous to a community of microorganisms. Eukaryotic cells are not simply larger, more complex prokaryotic cells. We recognize cell biology to be endocytobiology: the study of several kinds of cells within cells (Schenck and Schwemmler, 1983). Cell biology becomes the study of tightly integrated microbial symbionts. We see in this chapter how our perspective changes the way we view embryogenesis, the origin of embryos. Development and differentiation from the symbiotic vantage point are not singular processes but rigidly controlled mechanisms of microbial community ecology.

    Cell differentiation in animals...

  19. 12 BIG EGGS AND SMALL SPERM Origin of Anisogamy and Gender
    (pp. 183-203)

    The protoctist ancestors of the animals and plants never solved the problem, on the single-cell level, of how to retain both their motility and their ability to divide by mitosis. The contention that replicating and motile MTOCs are mutually exclusive would be falsified by the observation of a motile, undulipodiated animal or plant cell in the process of mitotic division. The cells that were motile by undulipodia and were forced therefore to relinquish mitosis were ancestral to animals and plants. They adopted multicellularity as a solution. Because a given single cell could not solve the problem of simultaneously retaining mitotic...

  20. 13 THREE BILLION YEARS OF SEX Common Evolutionary Legacy and Strange Variations
    (pp. 204-226)

    As was astutely realized by Langridge, the complex problem of the origin of sex is ultimately connected to the problem of pre-Phanerozoic genome evolution (Langridge, 1982). We now summarize the historical perspective developed in this book that we share with Langridge in the hope of broadening the base for further discussion. In this final chapter we unite our conclusions with his implications; this should provide the basis for further explanation and research. We apply our general conclusions to some specific examples: trends of sexuality in symbiotic associations and the use of our analysis for understanding ciliate differentiation and loss of...

    (pp. 227-236)
    (pp. 237-248)
  23. INDEX
    (pp. 249-258)