Cover image for The fifth miracle : the search for the origin and meaning of life
The fifth miracle : the search for the origin and meaning of life
Davies, P. C. W.
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New York, NY : Simon & Schuster, [1999]

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304 pages : illustrations ; 25 cm
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QH325 .D345 1999 Adult Non-Fiction Central Closed Stacks

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How and where did life begin? Is it a chemical fluke, unique to Earth, or the product of intriguingly bio-friendly laws governing the entire universe? In his latest far-reaching book, "The Fifth Miracle," internationally acclaimed physicist and writer Paul Davies confronts one of science's great outstanding mysteries -- the origin of life.

Davies shows how new research hints that the crucible of life lay deep within Earth's hot crust, and not in a "warm little pond," as first suggested by Charles Darwin. Bizarre microbes discovered dwelling in the underworld and around submarine volcanic vents are thought to be living fossils. This discovery has transformed scientists' expectations for life on Mars and elsewhere in the universe. Davies stresses the key role that the bombardment of the planets by giant comets and asteroids has played in the origin and evolution of life, arguing that these "deep impacts" delivered the raw material for biology, but also kept life confined to its subterraneanhaven for millions of years.

Recently, scientists have uncovered tantalizing clues that life may have existed and may still exist -- elsewhe

Author Notes

Paul Davies is an internationally acclaimed physicist, writer and broadcaster. He received degrees in physics from University College, London.

He was Professor of Natural Philosophy in the Australian Centre for Astrobiology at Macquarie University, Sydney and has held previous academic appointments at the Universities of Cambridge, London, Newcastle upon Tyne and Adelaide. Most of his research has been in the area of quantum field theory in curved spacetime.

Davies has also has written many books for the general reader in the fascinating fields of cosmology and physics. He is the author of over twenty-five books, including The Mind of God, Other Worlds, God and the New Physics, The Edge of Infinity, The Cosmic Blueprint, Are We Alone?, The Fifth Miracle, The Last Three Minutes, About Time, and How to Build a Time Machine.

His awards include an Advance Australia Award for outstanding contributions to science, two Eureka Prizes, the 2001 Kelvin Medal and Prize by the Institute of Physics, and the 2002 Faraday Prize by The Royal Society for Progress in religion. He also received the Templeton Prize for his contributions to the deeper implications of science. In April 1999 the asteroid 1992 OG was officially named (6870) Pauldavies in his honour.

(Bowker Author Biography)

Reviews 5

Publisher's Weekly Review

With ease and charm, and without dumbing down the pertinent technical and philosophical issues, popular-science writer Davies (Are We Alone?: The Philosophical Basis of the Search for Extraterrestrial Life, etc.) combines research results from disparate fields to explore possible approaches to the question of biogenesis. Although he was trained as a physicist, Davies skillfully draws together insights from hot areas in microbiologyÄsuch as the study of extremophiles (bacteria that thrive in dangerous levels of acidity, cold, heat, radioactivity), the discovery of a third domain of life and the controversy over whether traces of carbon on Martian meteorites are actually fossilized bacteriaÄin his pursuit of a fundamental question: What is the origin of biological (and thus genetic) information? He is skeptical that purely biochemical forces could spark the leap from nonlife to life. At stake is another question: Is the universe bio-friendly? Davies believes that the answers to these questions involve identifying a new "law" of nature, which may come from advances in information and complexity theory. He contends it is possible that quantum mechanics also may be found to play a role in the relationship between life and the universe at large. This book is sure to engage and provoke readers curious about the raging controversies over the origin of life, on Earth or elsewhere. Seven line drawings. (Mar.) (c) Copyright PWxyz, LLC. All rights reserved

Choice Review

Davies takes the reader on a quest for fundamental phenomena that could explain the development of life in the universe and answer the question of how the first DNA-like structure gained the information needed to function. Throughout, there is the assumption that ". . . life and mind emerge not as the result of freakish accidents, but as natural manifestations of matter, written into the fabric of the universe." He begins with the problem of defining life, then considers where life might have begun through discussions of such diverse subjects as astronomy, thermodynamics, chemistry, and genetics, approaching the problem of tracing evolutionary pathways from the viewpoint of genetic and metabolic development in organisms. With considerable evidence to back him, Davies suggests that the so-called universal ancestor of all life on Earth was similar to known organisms that exist under extreme conditions now present on Earth, giving us the possibility of tracing development of life through study of these organisms. The book contains simplified but clear discussions of such complicated subjects as the genetic code and the second law of thermodynamics, and it is recommended for anyone interested in the question of how life began. All levels. P. R. Douville; emeritus, Central Connecticut State University

Booklist Review

Life on Earth--God's fifth miracle according to Genesis--may have begun with rock-eating microbes far below the surface of Mars. So suggests Davies in this provocative investigation into the origins of life. To show how Mars could have cradled the first life in this solar system, Davies not only visits the red planet but also explores the remoter regions of our own teeming planet--frigid glaciers of Antarctica and fiery geothermal vents at the bottom of the sea. He also visits the laboratory to scrutinize the mysterious processes through which inert chemicals might assemble themselves into living organisms. But above the technical biochemical issues looms a profound philosophical question: Did life on earth--including human life--originate through sheer accident? Or does life constitute the inevitable outcome of natural laws favoring complexity and self-organization throughout the galaxy? In his remarkably lucid style, Davies lays out the evidence for a universe inherently friendly to life. A ground-breaking book sure to extend Davies' already sizable following. --Bryce Christensen

Library Journal Review

In 1966, NASA scientists announced that they had detected evidence of microbial life in a Martian meteorite. In 1977, researchers discovered bizarre biological organisms living near hydrothermal vents in the deep ocean. What do these two events have in common? Possibly, they offer an explanation for the origin of life on Earth and even elsewhere in the universe. This subject is somewhat of a departure for Davies, who has written several books popularizing physics, astronomy, and the philosophy of science. Still, nobody is better at the simple art of explanation, and this skill serves Davies well in tying together so many diverse strands of theory. Other books have dealt with aspects of this subject (see Joseph Cone's Fire Under the Sea, LJ 7/91, and Amir Aczel's Probability 1, Harcourt, 1998), but Davies connects them admirably. For all public and academic libraries.‘Gregg Sapp, Univ. of Miami Lib., Coral Gables, FL (c) Copyright 2010. Library Journals LLC, a wholly owned subsidiary of Media Source, Inc. No redistribution permitted.

School Library Journal Review

YA-In recent years, scientists have made huge strides in understanding the origin and scientific nature of life. New discoveries have been made about its persistence in places previously believed impossible-deep inside the Earth's crust, inside volcanic vents, under extremely high and low temperatures, in radioactive environments, in space, and perhaps even in meteorites from Mars. These discoveries have overturned many past assumptions and offer future scientists a whole new set of challenges and possibilities. Touching upon the variety of approaches it is possible to take to this new information, Davies shows how the philosophical debates of past generations are still being played out by physicists, chemists, and biologists. Although much of the material here is highly technical-especially in the first chapters, which deal with the mysteries and complexities of genetic information-the author writes with a clarity that makes it possible to grasp the outlines even when all of the details might not be fully understood. In an approachable style, using logic, analogy, and fascinating fact, he poses ideas in terms that teens should find reader-friendly. Those reading at a high comprehension level who are interested in philosophy, pure science, computer science, space science, or science fiction will be brought up to speed regarding recent developments in the field, and gain a broad perspective on these important questions.-Christine C. Menefee, Fairfax County Public Library, VA (c) Copyright 2010. Library Journals LLC, a wholly owned subsidiary of Media Source, Inc. No redistribution permitted.



CHAPTER 1: The Meaning of Life Imagine boarding a time machine and being transported back four billion years. What will await you when you step out? No green hills or sandy shores. No white cliffs or dense forests. The young planet bears little resemblance to its equable appearance today. Indeed, the name "Earth" seems a serious misnomer. "Ocean" would suit better, for the whole world is almost completely submerged beneath a deep layer of hot water. No continents divide the scalding seas. Here and there the peak of a mighty volcano thrusts above the surface of the water and belches forth immense clouds of noxious gas. The atmosphere is crushingly dense and completely unbreathable. The sky, when free of cloud, is lit by a sun as deadly as a nuclear reactor, drenching the planet in ultraviolet rays. At night, bright meteors flash across the heavens. Occasionally a large meteorite penetrates the atmosphere and plunges into the ocean, raising gigantic tsunamis, kilometers high, which crash around the globe. The seabed at the base of the global ocean is unlike the familiar rock of today. A Hadean furnace lies just beneath, still aglow with primeval heat. In places the thin crust ruptures, producing vast fissures from which molten lava erupts to invade the ocean depths. The seawater, prevented from boiling by the enormous pressure of the overlying layers, infuses the labyrinthine fumaroles, creating a tumultuous chemical imbroglio that reaches deep into the heaving crust. And somewhere in those torrid depths, in the dark recesses of the seabed, something extraordinary is happening, something that is destined to reshape the planet and, eventually perhaps, the universe. Life is being born. The foregoing description is undeniably a speculative reconstruction. It is but one of many possible scenarios offered by scientists for the origin of life, but increasingly it seems the most plausible. Twenty years ago, it would have been heresy to suggest that life on Earth began in the torrid volcanic depths, far from air and sunlight. Yet the evidence is mounting that our oldest ancestors did not crawl out of the slime so much as ascend from the sulfurous underworld. It may even be that we surface dwellers are something of an aberration, an eccentric adaptation that arose only because of the rather special circumstances of Earth. If there is life elsewhere in the universe, it may well be almost entirely subterranean, and only rarely manifested on a planetary surface. Although there is now a measure of agreement that Earth's earliest bioforms were deep-living microbes, opinion remains divided over whether life actually began way down in the Earth's crust, or merely took up residence there early on. For, in spite of spectacular progress over the past few decades in molecular biology and biochemistry, scientists still don't know for sure how life began. The outline of a theory is available, but we are a long way from having a blow-by-blow account of the processes that transformed matter into life. Even the exact location of the incubator remains a frustrating mystery. It could be that life didn't originate on Earth at all; it may have come here from space. The challenge facing scientists struggling to explain the origin of life is the need to piece together a narrative of events that happened billions of years ago and have left little or no trace. The task is a daunting one. Fortunately, during the last few years some remarkable discoveries have been made about the likely nature of Earth's most primitive organisms. There have also been great strides in laboratory procedures, and a growing understanding of conditions in the early solar system. The recent revival of interest in the possibility of life on Mars has also served to broaden the thinking about the conditions necessary for life. Together, these developments have elevated the subject from a speculative backwater of science to a mainstream research project. The problem of how and where life began is one of the great outstanding mysteries of science. But it is more than that. The story of life's origin has ramifications for philosophy and even religion. Answers to such profound questions as whether we are the only sentient beings in the universe, whether life is the product of random accident or deeply rooted law, and whether there may be some sort of ultimate meaning to our existence, hinge on what science can reveal about the formation of life. In a subject supercharged with such significance, lack of agreement is unsurprising. Some scientists regard life as a bizarre chemical freak, unique in the universe, whereas others insist that it is the expected product of felicitous natural laws. If the magnificent edifice of life is the consequence of a random and purely incidental quirk of fate, as the French biologist Jacques Monod claimed, we must surely find common cause with his bleak atheism, so eloquently expressed in these words: "The ancient covenant is in pieces: man at last knows that he is alone in the unfeeling immensity of the universe, out of which he has emerged only by chance. Neither his destiny nor his duty have been written down." But if it transpires that life emerged more or less on cue as part of the deep lawfulness of the cosmos -- if it is scripted into the great cosmic drama in a basic manner -- it hints at a universe with a purpose. In short, the origin of life is the key to the meaning of life. In the coming chapters I shall carefully examine the latest scientific evidence in an attempt to confront these contentious philosophical issues. Just how bio-friendly is the universe? Is life unique to Planet Earth? How can something as complex as even the simplest organism be the product of straightforward physical processes? Life's mysterious origin The origin of life be almost a miracle, so many are the conditions which would have had to be satisfied to get it going. FRANCIS CRICK According to the Australian Aborigines of the Kimberley, in the Creation Time of Lalai, Wallanganda, the sovereign of the galaxy and maker of the Earth, let fresh water fall from space upon Wunggud, the giant Earth Snake. Wunggud, whose very body is made of the primeval material, was coiled into a ball of jellylike substance, ngallalla yawun. On receiving the invigorating water, Wunggud stirred. She formed depressions in the ground, garagi, to collect the water. Then she made the rain, and initiated the rhythmic processes of life: the seasons, the reproductive cycles, menstruation. Her creative powers shaped the landscape and brought forth all creatures and growing things, over which she still holds dominion. All cultures have their creation myths, some more colorful than others. For centuries, Western civilization looked to the Bible for enlightenment on the subject. The biblical text seems disappointingly bland when set beside the Australian story: God created life in more or less its present form ab initio, as the fifth miracle. Not far from the Kimberley -- across the Great Sandy Desert, in the mountains of the Pilbara -- lie the oldest known fossils on Earth. These extraordinary remains form part of the scientific account of creation. Science takes as its starting point the assumption that life wasn't made by a god or a supernatural being: it happened unaided and spontaneously, as a natural process. Over the past two centuries, scientists have painstakingly pieced together the history of life. The fossil record shows clearly that ancient life was very different from extant life. Generally speaking, the farther back in time you go, the simpler were the living things that inhabited Earth. The great proliferation of complex life forms occurred only within the last billion years. The oldest well-documented true animal fossils, also to be found in Australia (in the Flinders Ranges, north of Adelaide), are dated at 560 million years. Known as Ediacara, they include creatures resembling jellyfish. Shortly after this epoch, about 545 million years ago, there began a veritable explosion of species, culminating in the colonization of the land by large plants and animals. But before about one billion years ago, life was restricted to single-celled organisms. This record of complexification and diversification is broadly explained by Darwin's theory of evolution, which paints a picture of species continually branching and rebranching to form more and more distinct lineages. Conversely, in the past these lineages converge. The evidence strongly affirms that all life on Earth descended via this branching process from a common ancestor. That is, every person, every animal and plant, every invisible bacterium can be traced back to the same tiny microbe that lived billions of years ago, and thence back to the first living thing. What remains to be explained -- what stands out as the central unsolved puzzle in the scientific account of life -- is how the first microbe came to exist. Peering into life's innermost workings serves only to deepen the mystery. The living cell is the most complex system of its size known to mankind. Its host of specialized molecules, many found nowhere else but within living material, are themselves already enormously complex. They execute a dance of exquisite fidelity, orchestrated with breathtaking precision. Vastly more elaborate than the most complicated ballet, the dance of life encompasses countless molecular performers in synergetic coordination. Yet this is a dance with no sign of a choreographer. No intelligent supervisor, no mystic force, no conscious controlling agency swings the molecules into place at the right time, chooses the appropriate players, closes the links, uncouples the partners, moves them on. The dance of life is spontaneous, self-sustaining, and self-creating. How did something so immensely complicated, so finessed, so exquisitely clever, come into being all on its own? How can mindless molecules, capable only of pushing and pulling their immediate neighbors, cooperate to form and sustain something as ingenious as a living organism? Solving this riddle is an exercise in many disciplines -- biology foremost, but chemistry, geology, astronomy, mathematics, computing, and physics contribute too. It is also an exercise in history. Few scientists believe that life began in a single monumental leap. No physical process abruptly "breathed life" into inert matter. There must have been a long and complicated transitional stage between the nonliving and the first truly living thing, an extended chronology of events unlikely to be preordained in its myriad details. A law of nature could not alone explain how life began, because no conceivable law would compel a legion of atoms to follow precisely a prescribed sequence of assemblage. So, although complying with the laws of nature, the actual route to life must have owed much to chance and circumstance -- or contingency, as philosophers call it. Because of this, and because of our ignorance about the conditions that prevailed in the remote past, we will never know exactly which particular sequence of events produced the first life form. The mystery of biogenesis runs far deeper than ignorance over details, however. There is also a profound conceptual problem concerning the very nature of life. I have on my desk one of those lamps, popular in the 1960s, containing two differently colored fluids that don't mix. Blobs of one fluid slowly rise and fall through the other. People often comment that the behavior of the blobs is "lifelike." The lamp is not alone in this respect. Many inanimate systems have lifelike qualities -- flickering flames, snowflakes, cloud patterns, swirling eddies in a river. What is it that distinguishes genuine living organisms from merely lifelike systems? It is not simply a matter of degree; there is a real difference between the nature of the living and the merely lifelike. If a chicken lays an egg, it is a fair bet that the hatched fledgling will also be a chicken; but try predicting the precise shape of the next snowflake. The crucial difference is that the chicken is made according to specific genetic instructions, whereas lamp blobs, snowflakes, and eddies form willy-nilly. There is no gene for a snowflake. Biological complexity is instructed complexity or, to use modern parlance, it is information-based complexity. In the coming chapters I shall argue that it is not enough to know how life's immense structural complexity arose; we must also account for the origin of biological information. As we shall see, scientists are still very far from solving this fundamental conceptual puzzle. Some people rejoice in such ignorance, imagining that it leaves room for a miraculous creation. However, it is the job of science to solve mysteries without recourse to divine intervention. Just because scientists are still uncertain how life began does not mean life cannot have had a natural origin. How does one go about assembling a scientific account of the genesis of life? At first sight the task seems hopeless. The traditional method of seeking rock fossils offers few clues. Most of the delicate prebiotic molecules that gave rise to life will long ago have been eradicated. The best we can hope for is some degraded chemical residue of the ancestral organisms from which familiar cellular life evolved. If we had to rely on rock fossils alone, the task of understanding the origin and early evolution of life would indeed be formidable. Fortunately, there is another line of evidence altogether. It too stretches back into the dim and distant past, but it exists right here and now, inside extant life forms. Biologists are convinced that relics of ancient organisms live on in the structures and biochemical processes of their descendants -- including human beings. By studying how the modern cell operates, we can glimpse remnants of ancestral life at work -- a peculiar molecule here, an odd chemical reaction there -- in the same way that out-of-place coins, rusty tools, or suspicious mounds of earth alert the archaeologist. So, amid the intricate processes going on inside modern organisms, traces of primeval life survive, forming a bridge with our distant past. Analyzing these obscure traces, scientists have made a start on reconstructing the physical and chemical pathways that may have brought the first living cell into existence. Even with such biochemical clues, the task of reconstruction would still be largely guesswork were it not for the recent discovery of certain "living fossils" -- microbes that inhabit weird and extreme environments. These so-called superbugs are being intensively investigated, and look set to revolutionize microbiology. It could be that we are glimpsing in these offbeat microbes something close to the primitive organisms that spawned all life on Earth. More clues may come from the search for life on Mars and other planets, and the study of comets and meteorites. By piecing together all these strands of evidence, we may yet be able to deduce, in broad outline at least, the way in which life first emerged in the universe. What is life? Before we tackle the problem of its origin, it is important to have a clear idea of what life is. Fifty years ago, many scientists were convinced the mystery of life was about to be solved. Biologists recognized that the key lay among the molecular components within the cell. Physicists had by then made impressive strides elucidating the structure of matter at the atomic level, and it looked as if they would soon clear up the problem of life too. The agenda was set by the publication of Erwin Schrödinger's book What Is Life? in 1944. Living organisms, it seemed at the time, would turn out to be nothing more than elaborate machines with microscopic parts that could be studied using the techniques of experimental physics. Careful investigation lent support to this view. The living cell is indeed crammed with miniature machines. All it required was an assembly manual and the problem would be solved. Today, however, the picture of the cell as nothing but a very complicated mechanism seems rather naïve. To be sure, molecular biology has scored some dazzling successes, but scientists still can't quite put their finger on exactly what it is that separates a living organism from other types of physical objects. Though treating organisms as mechanisms has undoubtedly proved very fruitful, it is important not to be mesmerized by its simplistic charm. Mechanistic explanation is an important part of understanding life, not the whole story. Let me give a striking example of where the problem lies. Imagine throwing a dead bird and a live bird into the air. The dead bird will land with a thud, predictably, a few meters away. The live bird may well end up perched improbably on a television aerial across town, on the branch of a tree, on a rooftop, in a hedgerow, or in a nest. It would be hard to guess in advance exactly where. As a physicist, I am used to thinking of matter as passive, inert and clodlike, responding only when coerced by external forces -- as when the dead bird plunges to the ground under the tug of gravity. But living creatures literally have a life of their own. It is as if they contain some inner spark that gives them autonomy, so that they can (within limits) do as they please. Even bacteria do their own thing in a restricted way. Does this inner freedom, this spontaneity, imply that life defies the laws of physics, or do organisms merely harness those laws for their own ends? If so, how? And where do such "ends" come from in a world apparently ruled by blind and purposeless forces? This property of autonomy, or self-determination, seems to touch on the most enigmatic aspect that distinguishes living from nonliving things, but it is hard to know where it comes from. What physical properties of living organisms confer autonomy upon them? Nobody knows. Autonomy is one important characteristic of life. But there are many others, including the following: Reproduction. A living organism should be able to reproduce. However, some nonliving things, like crystals and bush fires, can reproduce, whereas viruses, which many people would regard as living, are unable to multiply on their own. Mules are certainly living, even though, being sterile, they cannot reproduce. A successful offspring is more than a mere facsimile of the original; it also includes a copy of the replication apparatus. To propagate their genes beyond the next generation, organisms must replicate the means of replication, as well as replicating the genes themselves. Metabolism. To be considered as properly alive, an organism has to do something. Every organism processes chemicals through complicated sequences of reactions, and as a result garners energy to enable it to carry out tasks, such as movement and reproduction. This chemical processing and energy liberation is called metabolism. However, metabolism cannot be equated with life. Some micro-organisms can become completely dormant for long periods of time, with their vital functions shut down. We would be reluctant to pronounce them dead if it is possible for them to be revived. Nutrition. This is closely related to metabolism. Seal up a living organism in a box for long enough and in due course it will cease to function and eventually die. Crucial to life is a continual throughput of matter and energy. For example, animals eat, plants photosynthesize. But a flow of matter and energy alone fails to capture the real business of life. The Great Red Spot of Jupiter is a fluid vortex sustained by a flow of matter and energy. Nobody suggests it is alive. In addition, it is not energy as such that life needs, but something like useful, or free, energy. More on this later. Complexity. All known forms of life are amazingly complex. Even single-celled organisms such as bacteria are veritable beehives of activity involving millions of components. In part, it is this complexity that guarantees the unpredictability of organisms. On the other hand, a hurricane and a galaxy are also very complex. Hurricanes are notoriously unpredictable. Many nonliving physical systems are what scientists call chaotic -- their behavior is too complicated to predict, and may even be random. Organization. Maybe it is not complexity per se that is significant, but organized complexity. The components of an organism must cooperate with each other or the organism will cease to function as a coherent unity. For example, a set of arteries and veins are not much use without a heart to pump blood through them. A pair of legs will offer little locomotive advantage if each leg moves on its own, without reference to the other. Even within individual cells the degree of cooperation is astonishing. Molecules don't simply career about haphazardly, but show all the hallmarks of a factory assembly line, with a high degree of specialization, a division of labor, and a command-and-control structure. Growth and development. Individual organisms grow and ecosystems tend to spread (if conditions are right). But many nonliving things grow too (crystals, rust, clouds). A subtler yet altogether more significant property of living things, treated as a class, is development. The remarkable story of life on Earth is one of gradual evolutionary adaptation, as a result of variety and novelty. Variation is the key. It is replication combined with variation that leads to Darwinian evolution. We might consider turning the problem upside down and say: if it evolves in the way Darwin described, it lives. Information content. In recent years scientists have stressed the analogy between living organisms and computers. Crucially, the information needed to replicate an organism is passed on in the genes from parent to offspring. So life is information technology writ small. But, again, information as such is not enough. Though there is information aplenty in the positions of the fallen leaves in a forest, it doesn't mean anything. To qualify for the description of living, information must be meaningful to the system that receives it: there must be a "context." In other words, the information must be specified. But where does this context itself come from, and how does a meaningful specification arise spontaneously in nature? Hardware/software entanglement. As we shall see, all life of the sort found on Earth stems from a deal struck between two very different classes of molecules: nucleic acids and proteins. These groups complement each other in terms of their chemical properties, but the contract goes much deeper than that, to the very heart of what is meant by life. Nucleic acids store life's software; the proteins are the real workers and constitute the hardware. The two chemical realms can support each other only because there is a highly specific and refined communication channel between them mediated by a code, the so-called genetic code. This code, and the communication channel -- both advanced products of evolution -- have the effect of entangling the hardware and software aspects of life in a baffling and almost paradoxical manner. Permanence and change. A further paradox of life concerns the strange conjunction of permanence and change. This ancient puzzle is sometimes referred to by philosophers as the problem of being versus becoming. The job of genes is to replicate, to conserve the genetic message. But without variation, adaptation is impossible and the genes will eventually get snuffed out: adapt or die is the Darwinian imperative. How do conservation and change coexist in one system? This contradiction lies at the heart of biology. Life flourishes on Earth because of the creative tension that exists between these conflicting demands; we still do not fully understand how the game is played out. It will be obvious that there is no easy answer to Schrödinger's question: what is life? No simple defining quality distinguishes the living from the nonliving. Perhaps that is just as well, because science presents the natural world as a unity. Anything that drives a wedge between the domains of the living and the nonliving risks biasing us towards the belief that life is magical or mystical, rather than something entirely natural. It is a mistake to seek a sharp dividing line between living and nonliving systems. You can't strip away the frills and identify some irreducible core of life, such as a particular molecule. There is no such thing as a living molecule, only a system of molecular processes that, taken collectively, may be considered alive. I can summarize this list of qualities by stating that, broadly speaking, life seems to involve two crucial factors: metabolism and reproduction. We can see that in our own lives. The most basic things that human beings do are breathe, eat, drink, excrete, and have sex. The first four activities are necessary for metabolism; the last is necessary for reproduction. It is doubtful that we would consider a population of entities that have metabolism but no reproduction, or reproduction without metabolism, to be living in the full sense of the term. The life force and other discredited notions Given the elusive character of life, it is not surprising that some people have resorted to mystical interpretations. Perhaps organisms are infused with some sort of essence or soul that brings them alive? The belief that life requires an extra ingredient over and above ordinary matter obeying normal physical laws is known as vitalism. It is a beguiling idea with a long history. The Greek philosopher Aristotle proposed that a special quality which he called the life force, or psyche, bestowed upon living organisms their remarkable properties, especially that of autonomy or self-movement. Aristotle's psyche was different from the later Christian idea of the soul as a special and separate entity. Indeed, in Aristotle's scheme, everything in the universe was considered to possess intrinsic properties that determined its behavior. In effect, he regarded the whole cosmos as an organism. Over the centuries, the notion of a life force reappeared in many different guises. From time to time attempts were made to link it with specific substances -- for example, air. Perhaps this was not unreasonable; after all, breathing stops on death, and artificial respiration can sometimes restore vital functions. Later, blood became the life-giving substance. These ancient myths live on in expressions like "breathing life" into something, or "draining away the lifeblood," as if there were more than one kind of blood. As scientific understanding advanced, so the life force became associated with more sophisticated concepts. Claims were made that it was attributable to phlogiston, or the ether -- imaginary substances that themselves became discredited in due course. Another idea, popular in the eighteenth century, was to identify the life force with electricity. At that time electrical phenomena were sufficiently mysterious to serve such a purpose, and Volta's famous experiments demonstrated that electricity could make severed frog muscles twitch. The belief that electricity could revivify matter was dramatically exploited by Mary Shelley in her famous novel Frankenstein, in which the monster, assembled from dead human organs, is brought to life with a huge spark from a thunderstorm. In the late nineteenth century, radioactivity replaced electricity as the latest mysterious phenomenon; sure enough, claims were made that a solution of gelatine could be instilled with life by exposing it to emissions from radium crystals. These early attempts to pin down the life force appear to us today as plain daft. Nevertheless, the assumption that life requires something in addition to normal physical forces survived well into the twentieth century. For a long time, chemicals made by organisms were regarded as somehow different from the rest. Even today, the subject of chemistry is divided into "organic" and "inorganic." The implication was that organic substances like alcohol, formaldehyde, and urea somehow retain the magical essence of life even when separated from any living organism. By contrast, inorganic substances such as common salt are well and truly dead. It came as something of a shock to vitalists when, in 1828, Friedrich Wöhler managed to synthesize urea from ammonium cyanate, an inorganic substance. By breaching the invisible barrier between the inorganic and organic worlds, and demonstrating that life itself was not needed to make organic substances, Wöhler scotched the idea that organic chemicals are subtly different from the rest. No longer was it necessary to posit two distinct types of matter. A common set of principles would henceforth govern the chemistry of both the living and the nonliving world. We now know that atoms are cycled through the biosphere, in and out of living organisms, all the time. Every carbon atom in your body is identical to a carbon atom in the air or in a lump of chalk. There is no mysterious "zing" that renders your carbon atoms "alive" while those around you are dead; no lifelike quality that a carbon atom acquires when you eat it, and gives up when you exhale it. In spite of the blurring of the distinction between organic and inorganic chemistry, vitalism lived on, popularized by some well-known philosophers such as Henri Bergson in France. In fact, it entered a more scientific phase with the work of a German embryologist, Hans Driesch, in the early 1900s. Driesch was impressed that embryos could be mutilated early in their growth yet still recover to produce a normal organism. These and other remarkable properties of organic development led him to propose that the emergence of the correct form of the organism, in all its intricate complexity, must be under the control of a guiding life force, which he termed entelechy. Driesch realized that the ordering properties of entelechy would place it in conflict with normal physical forces and the law of conservation of energy. He suggested that entelechy operates by affecting the timing of molecular interactions in a way that introduces a cooperative, holistic pattern. Although embryo development remains incompletely understood, enough is known about it, and biological pattern formation in general, to convince biologists that entelechy, like any other version of the life-force concept, is an unnecessary complication. This hasn't prevented many nonscientists from clinging to vitalistic ideas today. Beliefs range from the quasi-scientific, such as Kirlian photography, where a photographic image showing a sort of corona glow around a person's hand is produced by placing it in a strong electric field, to the unashamedly mystical ideas of yin and yang energy flows, karmas, and auras that appear only to gifted psychics. Unfortunately for the mystics, no properly conducted scientific experiment has ever demonstrated a life force at work, nor do we need such a force to explain what goes on inside biological organisms. A further reason to reject vitalistic explanations of life is their totally ad hoc character. If the life force manifests itself only in living things, it has little or no explanatory value. To make this point clear, let me use the analogy of a steam locomotive. Ask: what is a steam locomotive and how does it work? An engineer could give a very detailed reply to Excerpted from The Fifth Miracle: The Search for the Origin and Meaning of Life by Paul Davies All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.

Table of Contents

Prefacep. 11
Chapter 1 The Meaning of Lifep. 25
Life's mysterious origin
What is life?
The life force and other discredited notions
The tale of the ancient molecule
Microbes and the search for Eden
Chapter 2 Against the Tidep. 49
The degeneration principle
Where does biological information come from?
The entropy gap: gravity as the fountainhead of order
Chapter 3 Out of the Slimep. 69
The tree of life
The three domains of life
The earliest rock fossils
Spontaneous generation
Re-creating the primordial soup
Chance and the origin of life
Chapter 4 The Message in the Machinep. 97
Replicate, replicate!
Making a living
The genetic code
Getting the message
A code within the code?
Chapter 5 The Chicken-and-Egg Paradoxp. 123
RNA first
RNA last
Self-organization: something for nothing?
Chapter 6 The Cosmic Connectionp. 143
The stardust in your eyes
Cosmic chemistry
Genesis from space
The Sisyphus effect
Chapter 7 Superbugsp. 163
Some like it hot
Life in the underworld
Ascent from Hades
Let them eat rock
The rest is history
Chapter 8 Mars: Red and Dead?p. 187
A bad place for a vacation
The Martian greenhouse
Was there life on Mars?
Is there still life on Mars?
Meteorites from Mars
Traces of life?
Killer plague from the red planet!
Chapter 9 Panspermiap. 221
Survival in space
Did life come to Earth in a meteorite?
Did Earthlife come from Mars?
Did Earthlife go to Mars?
Chapter 10 A Bio-Friendly Universe?p. 245
Did life ever begin?
Are the laws of nature rigged in favor of life?
Is it Darwinism all the way down?
A ladder of progress?
Is mind predestined?
Notesp. 275
Indexp. 293