Life Explained

Life Explained

Matthew Cobb
Malcolm DeBevoise
MICHEL MORANGE
Copyright Date: 2008
Published by: Yale University Press
Pages: 192
https://www.jstor.org/stable/j.ctt1npgcb
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  • Book Info
    Life Explained
    Book Description:

    Fifty years ago Francis Crick and James D. Watson proposed the double helix model for the DNA molecule. They believed they had, as Crick put it, discovered the "secret of life," and many agreed. But in the intervening years, science has marched-sometimes leaped-forward, and now the question "What is life?" must be posed once again.

    In this accessible and fascinating book, Michel Morange draws on recent advances in molecular genetics, evolutionary biology, astrobiology, and other disciplines to find today's answers to the question of life. He begins by discussing the various answers that have been formulated in the past, setting contemporary definitions of life within a rich philosophical and scientific tradition that reaches back to ancient Greece. Then, with impeccable logic and a wealth of appropriate detail, Morange proceeds to lay out the fundamental characteristics that define life. The road to an understanding of life remains incompletely charted, he concludes, but the nature of its final destination is no longer an enigma.

    eISBN: 978-0-300-14239-6
    Subjects: General Science

Table of Contents

  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-viii)
  3. Preface
    (pp. ix-xvi)
  4. Part I The Death and Resurrection of Life
    • [Part I Introduction]
      (pp. 1-2)

      In 1962, a French biologist named Ernest Kahane published a book titledLife Does Not Exist. Much more recently an American, Stanley Shostak, published one calledDeath of Life.Although both authors described the same phenomenon—the abandonment by biologists of research into the nature of life—their accounts of it were very different. For Kahane, the question of life, having been reduced to a physicochemical problem, had therefore either been solved or was in the process of being solved. Shostak, on the other hand, to judge from the subtitle of his book (“The Legacy of Molecular Biology”), felt that...

    • 1 The Twilight of Life
      (pp. 3-8)

      The expression “twilight of life” was first used in 1935, in an article that appeared in theNew York Times,to summarize the implications of the crystallization of the tobacco mosaic virus (TMV) by the American chemist Wendell Meredith Stanley.¹ This experiment showed that the TMV was no different from the molecules that were habitually manipulated and purified by organic chemists: it was merely a very large molecule.

      Stanley’s experiment was spectacular, and it received an enormous amount of publicity. But it was only one of a number of experimental approaches that, by the middle of the twentieth century, had...

    • 2 Life as Genetic Information
      (pp. 9-15)

      In July 2002, the American journalScienceannounced the in-vitro synthesis of the polio virus (more precisely, the synthesis of a nucleic acid that allows the virus to be produced once it has been inserted into a cell) from simple molecules.¹ The news made front pages around the world.

      This kind of media attention may seem rather surprising. After all, the experiment was not entirely novel. As we have already seen, similar studies of a bacterial virus had been made thirty-five years earlier. The excitement surrounding this announcement had to do instead with memories of the devastating effects of the...

    • 3 The Return of Life
      (pp. 16-24)

      Molecular biologists used to argue that the appearance of life and the appearance of genetic information were one and the same thing. The plausibility of this claim derived from the fact that all terrestrial organisms are descended from the same ancestor and use the same genetic code. But it was sophistry nonetheless, and did more to obscure the origin of life than to clarify it. The problem was not so much the first stages (the formation of molecules and macromolecules) as the appearance of precise rules of correspondence between these macromolecules. In particular, the molecular biologists’ view failed to explain...

  5. Part II The Question in Historical Perspective
    • [Part II Introduction]
      (pp. 25-26)

      My purpose in this second part of the book is not to make a list of all the answers, past and present, that have been given to the question “What is life?” An entire book of such answers would require knowledge that I do not have, and in any case it would not be long enough. I mean instead to bring out the various points of agreement and contradiction hidden among the many different answers that have been proposed.

      The American historian of science Gerald Holton suggested that the evolution of scientific ideas could be described as a series of...

    • 4 A Rich Heritage
      (pp. 27-34)

      The first answer to the question “What is life?”—or at least one of the oldest and best known—comes from Aristotle: “By life we mean self-nutrition and growth (with its correlative decay).”¹ On this view, life is a temporal process with a beginning and an end.

      InPhysiological Researches on Life and Death(1800), the French physiologist and pioneering histologist Xavier Bichat uttered his famous aphorism, “Life is the totality of functions that resist death.”² In saying this Bichat affirmed Aristotle’s opinion, but he focused less on the question of life’s beginning than on its end, describing survival as...

    • 5 Contemporary Answers
      (pp. 35-46)

      Although most biologists no longer think that looking for an answer to the question “What is life?” is either meaningless or, worse still, irrational, they are apt to be surprised by the difficulties involved. The American biochemist Daniel Koshland described a meeting of eminent figures in the field that was devoted to finding an answer that could be stated in a single sentence. Each time a new definition was proposed, it took the members of the audience only a few minutes to demonstrate its inadequacy. Finally, after several hours of debate, one answer met with general approval and was adopted...

  6. Part III Contributions of Current Research
    • [Part III Introduction]
      (pp. 47-48)

      In this part I take up answers to the question “What is life?” that grow out of present-day biological research. To some extent these are what might be called subliminal answers, in the sense that scientists do not feel obliged to discuss them openly, generally because they are taken for granted. Nonetheless scientific work would lose its meaning without them.

      There are some cases where the answer, even when it is not stated explicitly, is plain enough. For example, the experimental apparatus placed on a space probe to detect traces of life must have been conceived and developed with a...

    • 6 Looking for Life’s Past
      (pp. 49-58)

      Trying to reconstruct the path that led to the appearance of life on Earth makes sense only if terrestrial life first appeared—on Earth. There is a competing hypothesis, known as panspermia, put forward first by the Scottish physicist Lord Kelvin in the latter part of the nineteenth century, and subsequently developed by the Swedish chemist Svante Arrhenius in the early twentieth century.¹ According to this theory, life has always existed in the universe and has simply moved from planet to planet. The theory appeared to have been definitively refuted in 1924 by the French plant physiologist Paul Becquerel, whose...

    • 7 Retracing the Path of Life
      (pp. 59-71)

      The search for traces of the earliest forms of life on the Earth’s surface cannot hope to go beyond these forms, however, all the way back to the period of prebiotic evolution that preceded them. The attempt to do just this—the second of the three possible approaches for reconstructing how life was formed—has given rise to a great many investigations since Stanley Miller’s 1953 experiment demonstrating the formation of amino acids from simple molecules.

      These studies have had two different aims, which are not always clearly distinguished. The first is to describe the path followed by life during...

    • 8 Reading the Palimpsest of Life
      (pp. 72-77)

      In this chapter and the one following I take up the third line of research I mentioned earlier. It flows from a single assumption, namely, that in today’s world there exist organisms that are wholly or partly identical to the first forms of life—what are sometimes called living fossils. Micro-organisms that are indistinguishable from ancestral forms would be the microbial equivalent of the coelacanth, a fish well known from the fossil record that was thought to have been extinct for many millions of years and then, in the 1930s, was found to be alive in the depths of the...

    • 9 Life Under Extreme Conditions
      (pp. 78-84)

      It has long been known that organisms can resist extreme conditions. One has only to think of hibernation, or of the formation of spores, discovered by microbiologists toward the end of the nineteenth century. Recent studies have succeeded in describing some of the mechanisms involved. They have also pushed back the limits of life still further by demonstrating, for example, the abundance of organic forms found in ice and the resistance shown by some organisms to very high pressure.¹

      The study of hyperthermophilic extremophiles—organisms that preferentially develop at very high temperatures—has now become a very active field of...

    • 10 The Search for a Minimal Genome
      (pp. 85-89)

      In the opening chapters I discussed the ways in which the conception of life has changed over the past century, and emphasized the importance initially attached to viruses before it was recognized that they are in fact parasites, which fatally undermined the hopes that had been placed in them as a model system. The idea that the nature of vital properties can be understood by studying the simplest organisms is a legacy of Lamarck, and one that, unlike his theories of variation and evolution, is still widely accepted today. The advantage of such organisms, Lamarck argued, is that they present...

    • 11 Astrobiological Investigations
      (pp. 90-100)

      Speculation about extraterrestrial life has a very long history, going back at least as far as the ancient Greeks. The idea of the existence—and often the superiority—of celestial beings is a venerable feature of religious thought.¹ Like the Persians in Montesquieu’sPersian Letters(1721), aliens have often served as a vehicle for the hopes—and the fears—of mankind.² It is somewhat surprising, then, that one finds scarcely more interest in the question “What is life?” in the writings of astrobiologists today than in the writings of biologists generally. New experiments are proposed, but rarely supported by any...

    • 12 Life as a Living System
      (pp. 101-110)

      At first sight, this chapter may appear to be a miscellany of unrelated topics: the structure of eukaryotic cells, death of several kinds, and what genomic sequencing programs can tell us about the mechanisms involved in the evolution of organisms. My purpose, however, is to show—what in this case may be a matter more of reminding ourselves of what we already know—that life cannot be reduced to a mere collection of autonomous organisms.

      Every living being is a part of a community that gives organisms their genes and decides whether they live or die, even whether they are...

  7. Part IV A Few Necessarily Provisional Conclusions
    • [Part IV Introduction]
      (pp. 111-112)

      In the second part of the book I briefly reviewed the main answers, ancient and modern, that have been given to the question “What is life?” The lack of any consensus was plain. The hopes raised in the middle of the twentieth century by the informational conception of life—which led some biologists to suppose that the question had disappeared—have now faded, and the old problems remain with us today, or so it would seem.

      I then went on, in the third part, to consider some of the assumptions that guide current research into the origin of life on...

    • 13 Objections and Replies
      (pp. 113-120)

      A number of objections can be brought against the attempt to inquire into the nature of life. Some readers may be inclined to question the very existence of the phenomenon of life itself. Everyone will concede that in nature there are objects that are called organisms. Most of us would agree on the set of objects that can be described in this way, which by itself is enough to warrant scientific interest in them. Beyond that, however, it might be argued that trying to grasp precisely what these objects have in common is an idle, pointless, and ultimately nonsensical exercise....

    • 14 Darwinism in Its Proper Place
      (pp. 121-132)

      No scientist seriously denies Darwinism’s explanatory power with regard to evolutionary phenomena. Indeed, it is the only theory capable of explaining the development of organisms on Earth. But this does not mean that Darwinism by itself answers the question “What is life?” To claim otherwise is to confound a well-established scientific theory with an ideology. My purpose in this chapter is to try to clearly distinguish the two things, and to examine the cultural and social reasons why it is so easy to move, often without realizing it, from the scientific theory of Darwinism to the ideology of what the...

    • 15 The Lure of Complexity
      (pp. 133-140)

      The variety of answers that have recently been given to the question “What is life?” is perhaps the clearest sign that a genuine theory of life is still wanted. That, of course, is precisely what Schrödinger tried to develop more than a half century ago—a physical theory of life based on molecular order and negentropy.

      Twelve years before the appearance of Schrödinger’s book, in 1932, another founder of quantum mechanics, the Danish physicist Niels Bohr, delivered a seminal lecture entitled “Light and Life.”¹ Like Schrödinger, Bohr sought to exploit the new conceptual arsenal of physics to explain the phenomenon...

    • 16 The Three Pillars of Life
      (pp. 141-150)

      Having found the Darwinian answer to the question “What is life?” wanting, and equally little reason to expect that a decisive breakthrough will be forthcoming from theories of complexity, we are left to ponder the relatively broad consensus among scientists that organisms share three fundamental characteristics: they possess particularly complex molecular structures; they routinely support a large number of highly specific chemical reactions by drawing upon the external environment for both molecular material and energy; and they reproduce themselves.

      These three characteristics are closely allied with one another. Complex molecular structures supply the catalytic basis for metabolic reactions and the...

  8. Conclusion
    (pp. 151-156)

    In adopting a triadic conception of life, I have left to one side a number of characteristics that figure in the various accounts that were presented in the second part of this book or elsewhere in passing: the hierarchical organization of the living world; its richness and diversity; the morphogenetic inventiveness of organisms; their robustness in response to extreme variations in their internal and external environment; the apparent purposefulness of their structures and behaviors; and even the fact that they can fall ill.¹ All these characteristics of life are quite obvious in complex organisms, although they are also present in...

  9. Notes
    (pp. 157-178)
  10. Bibliography
    (pp. 179-196)
  11. Index
    (pp. 197-205)