Genetics of Original Sin by Duve, Christian De -- Read -- Imperial Library of Trantor

Index

Contents Foreword Preface Acknowledgments Introduction I The History of Life on Earth Introduction 1 The Unity of Life

Advancing knowledge has swept away “centrisms” Earth has a history Life also has a history All living beings share a number of basic properties The history of life is written into molecular sequences Biological evolution is an established fact Opposition to evolution on religious grounds is widespread

2 The Origin of Life

Life appeared on Earth shortly after the young planet had become physically able to harbor it The origin of life is not known, but the only scientifically acceptable hypothesis is that it arose naturally The building blocks of life arise spontaneously throughout the universe Earth formed a “cauldron” in which cosmic building blocks could interact The first steps in the origin of life were chemical in nature The appearance of RNA was a key step in the origin of life

3 The Evolution of Life

Microbes have left few fossil vestiges but many other traces of their long duration on Earth Bacteria separated into two main groups Atmospheric oxygen was a major contribution of life to Earth The birth of eukaryotic cells inaugurated a new living world Endosymbiosis was a key phenomenon in the development of eukaryotes Protists are the ultimate champions of unicellularity Multicellularity allowed division of labor Born in water, plants were the first multicellular organisms to invade land The evolution of animals developed around the alimentary function Marine invertebrates inaugurated animal life Body segmentation opened the way to vertebrates Several distinct animal lineages moved from water to land Dinosaurs gave rise to birds and mammals

II The Mechanisms of Life Introduction 4 Metabolism

Living cells are chemical factories Living cells extract the energy they need from their surroundings Thousands of specific catalysts are involved in metabolic reactions Metabolic pathways form networks of enormous complexity We are what our catalysts are The history of metabolism goes back to the earliest days of life

5 Reproduction

Reproduction started with molecular replication With the appearance of cells, cell division was added to molecular replication in biological reproduction Multicellular beings reproduce by way of single mother cells The mother cell of multicellular beings arises from two parental cells by sexual reproduction Chromosome doubling caused by sexual reproduction is corrected by meiosis during gamete maturation Sexual reproduction is the laboratory of evolution Male and female gametes differ Plant reproduction involves spores Seeds and fruits harbor, until germination, the plant embryos issued from fertilized eggs Fungi also reproduce by way of spores In animals, parent mobility favors union between spermatozoa and oocytes The fertilized egg of vertebrates has always developed in an aqueous medium

6 Development

The first accounts of embryological development were purely descriptive Experimental embryology began to decipher developmental mechanisms Development is ruled by transcriptional gene control Genes are organized by transcription into a hierarchy dominated by master genes Homeotic genes are master genes of central importance Evolution and development are intimately linked

7 Natural Selection

At the start lies heredity Artificial selection exploits the imperfections of heredity for defined purposes Malthus introduced the notion of the “struggle for life” Natural selection lets the “struggle for life” choose passively among the diversity created by the imperfections of heredity Natural selection acts under our very eyes The mutations subjected to natural selection are accidental events devoid of finality The role of chance in evolution is limited by stringent constraints Cases of optimizing selection are more frequent than long believed Evolution is largely molded by environmental conditions Certain evolutionary events could be potentially present in genomes and made manifest by favorable environmental conditions

8 Other Evolutionary Mechanisms

Lamarck advocated the heredity of acquired characters DNA cannot be a vector of Lamarckian heredity Cases of Lamarckian heredity that do not involve DNA exist Genetic drift accompanies evolution without selection Self-organization could theoretically drive evolutionary events Were some key evolutionary steps guided by “intelligent design”?

III The Human Adventure Introduction 9 The Emergence of Humans

Africa is the cradle of humankind They were not yet human, but they already made stone tools Prehumans started out of Africa for the first time some two million years ago A second wave of migrations started once again out of Africa The acquisition of language was a crucial step in hominization Cro-Magnon inaugurated modern humans What happened to the Neanderthals? Modern humans remain the only survivors from the adventure out of which they were born

10 Making the Human Brain

The brain is constructed with neurons The cerebral cortex is the mysterious site of conscience It took six hundred million years for the animal brain to reach, in chimpanzees, a volume of 21.4 cubic inches In the human line, it took two to three million years for the brain volume to expand from 21.4 to 82.4 cubic inches The expansion of the human brain went through a number of successive plateaus Exponential neuron multiplication braked by anatomical constraints probably explains the sigmoid shape of the jumps of brain volume from one plateau to another Expansion of the human brain was limited by the size of the female pelvis and by the degree of immaturity at birth compatible with survival

11 Shaping Our Genes

Hominization involved an astonishingly small number of individuals Hominization probably started with bipedalism, which was selectively advantageous in the local terrain Brain expansion dominated the second major stage of hominization The vagaries of environmental change probably guided the migrations that characterized the third stage of hominization Hominization: Chance or necessity? Summit or stage?

12 The Cost of Success

Taking advantage of the powers of their brains, humans have proliferated beyond all measure and exploited a major part of the planet’s resources for their own benefit The history of humanity is a perpetual succession of wars and conflicts The inordinate evolutionary success of the human species has been acquired at the expense of a severe deterioration of living conditions on Earth If it continues in the same direction, humankind is headed for frightful ordeals, if not its own extinction

13 Original Sin

Natural selection has indiscriminately privileged all the personal qualities that contribute to the immediate success of individuals Natural selection has privileged traits favoring cohesion within groups and hostility among different groups Natural selection has not privileged the foresight and wisdom needed for sacrificing immediate benefits for the sake of the future Original sin is none other than the fault written into human genes by natural selection The only possibility of redemption from the genetic original sin lies in the unique human ability to act against natural selection

IV The Challenges of the Future Introduction 14 Option 1: Do Nothing

If nothing is done, humanity is headed for disaster The extinction of humankind, if it occurs, will be due, not to its failure, but to its success Could a “superhuman” species succeed the human species? Life has up to five billion years left before Earth becomes incapable of harboring it What could happen in a brain even more developed than the human brain? With the advent of humankind, evolution has reached a point where it is no longer a slave to natural selection

15 Option 2: Improve Our Genes

Eugenics has become a dirty word Cloning opens the way to directed evolution What can cloning be used for? Human cloning provokes heated ethical debates Whatever happens, humanity will not be saved by cloning

16 Option 3: Rewire the Brain

The wiring of the brain is an epigenetic phenomenon Education starts in the cradle Political and, especially, religious leaders are particularly well placed to propagate the recommendations the world needs

17 Option 4: Call on Religions

Churches could play an exceptional role in saving humankind Religions are founded on beliefs, not on rational thought Many religions present themselves as defenders of the truth Religious doctrines have a major impact on ethical directives Hopes for a future life could hamper efforts in favor of present life Are religions to be fought or can they be enlisted? Churches are engaged in many valuable activities What should we do? Ethics without doctrine is possible The dialogue between science and religion is desirable but difficult Religions, through their influence, and the sciences, through their knowledge, must urgently collaborate for the salvation of humanity

18 Option 5: Protect the Environment

Protecting the environment is a very recent human concern Ecology has penetrated daily human life Ecology has become the source of major controversies Nuclear energy: pro or con? A basic discovery opened the way to revolutionary applications GMO: an acronym that ignites passions Are GMOs an assault against the sacredness of nature? Environmentalism has a crucial role to play

19 Option 6: Give Women a Chance

Combativeness is primarily a male character In most civilizations, women are treated as inferior to men The social rise of women in the modern world is an encouraging change

20 Option 7: Control Population

The crisis foreseen by Malthus has struck Culling is not a tolerable solution to the population problem One way or another, the birthrate must be reduced Limiting births needs to be encouraged

Epilogue Index

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