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First Signals

First Signals: The Evolution of Multicellular Development

John Tyler Bonner
Copyright Date: 2000
Pages: 156
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  • Book Info
    First Signals
    Book Description:

    The enormous recent success of molecular developmental biology has yielded a vast amount of new information on the details of development. So much so that we risk losing sight of the underlying principles that apply to all development. To cut through this thicket, John Tyler Bonner ponders a moment in evolution when development was at its most basic--the moment when signaling between cells began. Although multicellularity arose numerous times, most of those events happened many millions of years ago. Many of the details of development that we see today, even in simple organisms, accrued over a long evolutionary timeline, and the initial events are obscured. The relatively uncomplicated and easy-to-grow cellular slime molds offer a unique opportunity to analyze development at a primitive stage and perhaps gain insight into how early multicellular development might have started.

    Through slime molds, Bonner seeks a picture of the first elements of communication between cells. He asks what we have learned by looking at their developmental biology, including recent advances in our molecular understanding of the process. He then asks what is the most elementary way that polarity and pattern formation can be achieved. To find the answer, he uses models, including mathematical ones, to generate insights into how cell-to-cell cooperation might have originated. Students and scholars in the blossoming field of the evolution of development, as well as evolutionary biologists generally, will be interested in what Bonner has to say about the origins of multicellular development--and thus of the astounding biological complexity we now observe--and how best to study it.

    eISBN: 978-1-4008-3058-9
    Subjects: Biological Sciences

Table of Contents

  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-viii)
    (pp. ix-2)
    Margaree Harbour
  4. 1 Introduction
    (pp. 3-8)

    Since the 1940s, I have been thinking about how animals and plants and other organisms develop. As I look back over the many years, I see that the problem remains in some ways much the same, but in other ways it has changed to an extraordinary extent. The latter is entirely due to the fact that there has been such vast progress in the very nature of biology due to the eruption of molecular biology at midcentury. There has been a certain amount of tension between classical developmental biology and its modern molecular form, largely because the techniques are so...

  5. 2 From Embryology to Developmental Biology
    (pp. 9-18)

    Developmental biology started as a descriptive science but progressively became more experimental. Karl Ernst von Baer, in the early 1800s, was one of a long series of descriptive embryologists whose lineage went back to Aristotle; he was the first to see and describe the mammalian egg as well as the fundamental germ layers of embryos. But later in the century, the experimental approach took hold with the wonderful work of Wilhelm Roux, Hans Dreisch, and numerous others. When I was a student in the late thirties and early forties, this was almost the only way to study development. (I will...

  6. 3 The Origin of Multicellularity
    (pp. 19-48)

    The appearance of multicellularity during the course of early evolution is one of the major transitions during the whole span of biological evolution, as Maynard Smith and Szathmary (1995) and others have pointed out. These transitions are especially important in their implications for natural selection because with each transition one moves from one level of selection to another. This is the case with the invention of multicellularity, where one shifts from the cell as a unit of selection to a multicellular group of cells as a unit. Cells will either compete with one another or cooperate, and it is only...

  7. 4 Size and Evolution
    (pp. 49-62)

    The most obvious reason we have multicellular development lies in natural selection. If we could see and understand the external influences that caused development to arise and evolve, we would grasp the origins of development and win some insight into its primordial mechanics.

    Selection works in two cardinal ways on the life cycles of all organisms. There is a selection pressure for size increase under innumerable ecological circumstances, and becoming multicellular is an easy way to accomplish this. At the same time, as I have argued earlier (1958), there is a selection to retain a single-cell stage in the life...

  8. 5 The Evolution of Signaling
    (pp. 63-72)

    We often think of the origin of life as fundamentally a problem of the origin of template replication. That certainly is a central property of all living things, and there is no way life could have evolved without it. It has been elegantly pointed out by Dyson (1999) that replication of itself is not sufficient and that metabolism is another important property that was essential for life right from the beginning. Here I would like to add a third element that must have been equally important in distinguishing the living from the inert. It is the invention of a stimulus-response...

  9. 6 The Basic Elements of Multicellular Development
    (pp. 73-92)

    What we are seeking are the first principles of development. As I have pointed out, there are two ways of achieving this: one is by mathematical modeling, and the other is by looking at the beginning of multicellular development. Both approaches involve a considerable burden of hypothesis, for we were not there in the beginning. The simple organisms we see today have an ancient history, and an enormous time span has passed since they first arose—an almost infinite number of generations, time enough for many adjustments and alterations to cloud the way it was in the beginning. Let me...

  10. 7 Development in the Cellular Slime Molds
    (pp. 93-130)

    My plan here is to illustrate my main points by examining how they apply to one organism. I want to use the cellular slime molds to show how one can look at their development from the three points of view: the biological, the molecular, and the mathematical. By going into one case in some depth, we can see how the three approaches dovetail. Together they help us to understand not only how multicellular development arose in the first place, but how all three ways of looking at the matter help us to understand development itself.

    I have already described the...

  11. 8 Conclusion
    (pp. 131-134)

    Here are the bare bones of my argument. A basic premise from which all else follows is that most, if not all, the microorganisms that exist today have an ancestry that goes back many millions, if not billions of years. On this foundation I have argued that (1) the size of organisms is under constant selection pressure, and in early earth history, when all of life was unicellular, one easy and frequently occurring way of becoming larger was to become multicellular; (2) as soon as such cell conglomerates appeared, there was selection for integration between the cells, and this involved...

    (pp. 135-142)
  13. INDEX
    (pp. 143-146)