Genetics of Original Sin Read online

  This is all the more true because it’s not just about the life that surrounds us; it’s about our own nature, our own history as a form of life. One of the most important revelations of modern science has been the discovery that we are part of the great network of life. We are not only its spectators and beneficiaries, as long believed. We are born from it and share its basic properties with all other living beings on this planet. In addition, we have specifically human traits that we owe to our brains. Understanding life means understanding ourselves.

  There are more practical reasons why it is important for all of us, and in particular our political, cultural, economic, and religious leaders, to be informed about the nature and history of life. Our understanding of basic biological mechanisms has spawned powerful means to manipulate life. Cloning, in vitro fertilization, stem cells, DNA tests, genetically modified organisms: these terms and others have become part of common vocabulary and should be understood by everyone. This requirement does not just concern specialized notions. Many questions of interest for our daily existence—health, food, hygiene, economy, environment, and so on—are linked one way or another to what we know—or ought to know—about the properties of living beings. The term “bio” has gained an almost mystic connotation. But rare are those who may sensibly claim that they understand with some precision what it’s all about.

  The most important and urgent reason why it is now imperative that every responsible citizen be informed of recent developments in the life sciences is that we need this knowledge in order to face the future in a constructive way. The present book addresses this issue. It is the outcome of a thirty-year voyage of discovery, chronicled in five successive books, which has led me from lysosomes and peroxisomes, the cell organelles that were long the sole focus of my laboratory research, first to all aspects of cellular organization (A Guided Tour of the Living Cell), then to the basic properties of life and to its origin (Blueprint for a Cell: The Nature and Origin of Life), to its evolutionary history, including the advent of humankind (Vital Dust: Life as a Cosmic Imperative), and, finally, to the “meaning of it all” (Life Evolving: Molecules, Mind, and Meaning). At the end of the journey, I completed this series, which was largely addressed to the general public, with a concise summary aimed at a more scientifically literate readership (Singularities: Landmarks on the Pathways of Life). This was to be the end of my literary expedition. My neuronal telomeres decided differently. (Highlighted by the 2009 Nobel Prize in medicine, telomeres are DNA “tails” attached to the ends of chromosomes that shorten progressively in the course of successive cell divisions. Their preservation and/or repair are linked to increasing cellular longevity.)

  Having been granted the time to do so, I have been prompted to go one step further, this time back to the past and into the future. It turned out to be not just a pleasing intellectual pastime but an effort to meet a pressing need. The future of life on Earth, in particular human life, is under serious threat. Climate change, deforestation, desertification, water shortage, famine, loss of biodiversity, depletion of natural resources, growing energy needs, pollution, new diseases, overcrowded megalopolises, conflicts, and wars are daily brought to our attention by the media. These menaces are recognized and burgeoning. Yet responses so far have been sluggish, to say the least. The vague and slight results of the recent Copenhagen conference on climate illustrate humanity’s inability to come to grips with threats that extend beyond the immediate future.

  It occurred to me that the causes of this worrisome situation, both the menaces and our lack of constructive response, are to be found in our nature, itself the product of a long history that I had attempted to reconstruct and explain in previous books. The “culprit,” in this scientific interpretation of the myth of “original sin,” is natural selection, which has sustained in our genes the traits that proved immediately useful to the survival and reproduction of our ancestors but have now become dangerously harmful. If we wish to escape the fate that awaits us, we must take advantage of our unique ability to consciously and deliberately act against natural selection. Such is the object of this book.

  The work is addressed to as wide a readership as possible, not necessarily acquainted with science or trained in its way of thinking, but adequately informed of world affairs. For this reason, I have avoided all technical terms and left out the customary notes and references that would be needed in a more scholarly opus. I have also mostly refrained from mentioning quantitative data readily available elsewhere. But I do explain, in passing, some of the new biotechnological tools, such as cloning and genetic engineering, offered by modern science to a society that distrusts them and urgently needs clarification on the topic.

  I cannot end this preface without recalling with deep sorrow the memory of my dear Janine, lost to my affection after sixty-five years of life together, just as I was finishing the first draft of this book. She used to read each chapter as soon as it came out of my computer and never failed to make judicious comments, all the more valuable because, as a professional artist, she cast a fresh look on my writings. I dedicate what is probably my last work to her beloved memory, on the day of what would have been her eighty-eighth birthday.

  Nethen and New York, 6 April 2010

  Acknowledgments

  As I have done for earlier works, I wrote this book concurrently in my two mother languages, English and French. The two versions have benefited reciprocally from the criticisms, comments, and suggestions addressed to the other.

  Many people have helped to make this work possible. Among them, I owe special tribute to my faithful editor and longtime friend Neil Patterson, who once again has favored me with his invaluable help, not only in purging my style of gallicisms, grammatical errors, obscure statements, needless repetitions, and flowery expressions, but also in critically assessing the substance. His participation has far exceeded a strictly editorial assistance and has justified his designation as coauthor. I am particularly pleased to publish this new work with him, after more than twenty-five years of friendly and effective, if sometimes heated, collaboration.

  I am particularly indebted to my valued friend Odile Jacob, who not only has published two of my previous books before this one but has, in addition, decided to include my latest opus in her joint enterprise with Yale University Press. It is a great honor. I also address my most grateful thanks to the members of her staff, including Gérard Jorland, Émilie Barian, and Claudine Roth-Isler, for their excellent collaboration.

  I owe a similar debt of sincere gratitude to Yale University Press for publishing the English version of the book and, especially, to Jean Thomson Black for her competent and understanding assistance, to Laura Jones Dooley for her thorough editorial revision of the manuscript (with my apologies for not always following her recommendations), and to Jaya Chatterjee for her valuable help with illustrations.

  Finally, I wish to thank my trusted Brussels assistant, Monique Van de Maele, for her invaluable help in the search for needed information and her colleague, Nathalie Chevalier, who has expertly assembled the illustrations common to both versions. I am also indebted to Xavier de Felipe for his wonderful reconstruction of the “forest of neurons” reproduced in figure 10.1 and to Gabriel Ringlet for valuable criticisms and suggestions.

  Introduction

  The sacred writers who invented the famous myth, immortalized by numerous artists and writers across the centuries, of Original Sin that allegedly cost the first parents of humanity to be expelled from the Earthly Paradise, have not just displayed lively poetic imagination. They have, in addition, shown remarkable perspicacity—apart from their choice, which was far from innocent, of a woman as culprit. They have perceived the presence in human nature of a fatal flaw, which, as they saw it, only divine intervention could possibly repair. Hence the hope for an envoy from God, a Messiah, Savior, or Redeemer, whom some believe to have appeared two thousand years ago and others are still awaiting.

  Modern science has rendered the biblical acc
ount untenable, without, however, invalidating the intuition that may have inspired it. Humankind is indeed tainted by a fundamental defect, bound, in all probability, to bring about its demise. The culprit is not Eve, but natural selection. There is indeed a need for a redeemer. But that redeemer will not come from heaven; only humankind can serve that role.

  In this predicament, the wisdom of our forebears is of little help to us today, because the wise of yesteryear could not foresee the present crisis. But their recommendation that we should take advantage of the lessons of the past to prepare the future remains timely. What humanity needs now is a new form of wisdom inspired by what we have learned about the nature and history of the living world to which we belong, about our place in it, and about the manner in which we have reached it.

  Such is the thesis I develop in this book, adopting as main guide life itself, as we have learned to understand it, with as illuminating beacon natural selection, the mechanism discerned by the genius of Charles Darwin, who has been celebrated in 2009 by a dual anniversary, the 200th of his birth and the 150th of the first publication of his magnum opus, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life.

  This book is divided into four parts, each of which stands more or less on its own. To start, I retrace briefly a number of basic notions about the nature, origin, and evolutionary history of life on Earth. I do so in a strictly descriptive fashion, leaving an analysis of the underlying mechanisms to the second part.

  In Part II, I discuss such key processes as metabolism, reproduction, and development before addressing the central theme of the book: natural selection. I end with a brief consideration of some of the evolutionary mechanisms that have been proposed besides natural selection.

  The scene thus set, I move on, in Part III, to the extraordinary saga of the human adventure, which, initiated a few million years ago in the heart of Africa, has developed, sustained by a stupendous expansion of the brain, at an increasingly dizzying pace, leading, in the last centuries and, even more so, in the very last decades, to the fantastic success of our species and to the mortal menaces it causes to weigh on the future, the ultimate consequences of our “original sin.”

  Then, in Part IV, I sketch potential solutions toward redemption or, at least, the chance for it, which I see in the specifically human power to act against natural selection. But to exercise this power, we will have to find in the resources of our minds a wisdom that is not written in our genes.

  I

  The History of Life on Earth

  Introduction

  What is life? What are its principal properties? What reasons do we have for believing there is only one kind of life on Earth, issued from a single ancestral root? How did life arise? What are the main steps of its history? Such are some of the questions that I try to answer in this first part of the book. I do so in descriptive and phenomenological form, postponing until the following part an examination of underlying mechanisms.

  1

  The Unity of Life

  A ll known living organisms are descendants from a common ancestral form of life, often represented by the acronym LUCA (Last Universal Common Ancestor). Put forward as an affirmation, not just a theory or hypothesis, this statement may strike many readers unacquainted with modern biology as almost incredible, if not objectionable or even contrary to their most sacred beliefs. An explanation is in order.

  Advancing knowledge has swept away “centrisms”

  For most of their history, humans have seen Earth as the center of the universe, their privileged abode. In the second century, the Greek mathematician and astronomer Ptolemy integrated this “geocentric” view into a coherent theory that placed the Sun, the planets, and the stars in concentric spheres surrounding Earth. The Ptolemaic system dominated thinking for about fourteen hundred years, until the Polish astronomer Copernicus (1473–1543) rejected it in favor of the “heliocentric” view, which has the Sun in the center and the Earth and other planets circling around it. This view ran the risk of being seen as heretical at the time; it conflicted with the biblical account that Joshua “stopped the sun” to allow the Israelites to win the Battle of Gibeon against the Canaanite kings. For this reason, Copernicus prudently refrained from having his theory publicized until after his death. This may have been a sound decision, considering the fate that befell the Italian Galileo (1564–1642), almost one century later, when his advocacy of the Copernican view led, in 1633, to his condemnation by the Catholic Church, which, although yielding to the evidence much earlier, officially revoked this condemnation only some three and a half centuries later.

  Since the time of Galileo, the Sun itself has lost its central status. It has been found to be only one among some one hundred billion stars in our galaxy, which has itself been dethroned by the observations of the American astronomer Edwin Hubble, who discovered, in the 1920s, that the distant celestial objects then known as “nebulae” are actually other galaxies, of which about one hundred billion are believed to exist.

  While the status of our planet was progressively relegated from the center of the universe to the backyard of one in one hundred billion stars in one of one hundred billion galaxies, the “anthropocentric” view of a universe made for humans was also shaken. It all began with increasing realization that Earth is not, as was long believed, a fixed setting created for our human adventure. Earth was found to have a history of its own.

  Earth has a history

  This awareness dawned in the eighteenth century, from observations in places where flowing water has cut through rocks to expose their structure—the Grand Canyon is the most spectacular example—showing that the ground beneath us is stratified in layers of different texture and composition. The layers may be flat or curved, or inclined. Some contain the shells of marine animals embedded in the rock; think of marble, for instance. This telling clue enforced the astonishing conclusion that these layers had once been under water, where they had slowly formed through sedimentation of sand and dust particles, in which dead animals became buried, their bodies rotting, leaving only the mineral shells. As time went by and new layers accumulated on top, the old ones were pushed deeper and deeper, exposed to increasing heat and pressure, solidifying into rocks. Some of these rock layers were later driven upward by underground movements, to finally rise above the level of the waters in which they were born, even building mountains.

  These observations allowed terrains to be classified in terms of their relative age. These ages could not be known in absolute terms at that time, but it was clear that they must cover considerable durations, possibly measured in as much as millions of years, a span of time almost unimaginable in those days. But the facts were there. Mountains obviously do not arise overnight, not even in a few millennia. The Alps have probably not changed much since Hannibal’s army crossed them on elephants, more than two millennia ago, to take the Romans by surprise. Today, thanks to a method known as radioisotopic dating, geological times have been measured and found to be even longer than was first pictured, covering up to several billion years.

  Although rudimentary in comparison with present-day geological knowledge, these early findings were sufficient to throw a revealing light on another set of observations that had long intrigued nature watchers, those dealing with fossils. Many such vestiges had been discovered by amateur naturalists over the years in various places. Their origin was a matter of lively debate. They were readily identified as the remnants of dead plants and animals, many of which, however, seemed to be different from any extant species known. Whether the living precursors of the fossils were organisms that still lived elsewhere in unexplored areas or had become extinct was much discussed. Some even considered that fossils were the remains of victims of the Flood. Putting some order into all this fantasizing, a crucial piece of information was provided by geological observations revealing that the complexity of the organisms whose fossils were found in a given terrain was related to the
age of that terrain. The younger the terrain, the more complex the fossilized remains. These findings showed that life, like the Earth, also has a history, in the course of which organisms of increasing complexity progressively appeared.

  Life also has a history

  The notion of the “fixity of species” was, however, so dominant at the time that the significance of these observations was not immediately appreciated by most scientists. Only a few were sufficiently perceptive, as well as daring, to conceive the revolutionary hypothesis that life started with very simple forms that progressively evolved into forms of increasing complexity. This so-called transformist hypothesis was first formulated at the end of the eighteenth century, simultaneously in France, by Jean-Baptiste de Monet, chevalier de Lamarck (1744–1829), and, in England, by Erasmus Darwin (1731–1802), the grandfather of the famous Charles.