The origin of life on the earth

parts 2

INTRODUCTION XI This led to a serious crisis in the ideas of many scientists of our century concerning the problem with which we are dealing. Some of these scientists tried to get out of the question by suggesting that life never arose on Earth but that the first living things were brought here from somewhere else such as the surface of one of the nearer or more distant planets. Others got round the question of the origin of life by adopting openly idealistic positions and declaring that the problem belonged, not to the province of science but to that of faith. It was, of course, not the nature of the problem which led to this crisis but the fact that scientists were using faulty methods in their approach to it. It was the outstanding service of Charles Darwin to biology that he broke with the earlier metaphysical methods for attacking the problem of the origin of the existing forms of animals and plants. He showed, beyond question, that highly organised living creatures can appear on the Earth only as the result of prolonged development, that is, evolution of higher forms from lower ones. In the absence of such evolution it was impossible to maintain that human beings or other highly developed organisms had arisen by natural means without the intervention of any spiritual or supernatural agency. However, even after Darwin's work, scientists approached the problem of the origin of the very simplest living things, which were the first ancestors of every living thing on Earth, in the same metaphysical way which had prevailed in regard to more highly organised organisms before Darwin's time. We have, however, already seen that, even after the work of Darwin, people tried to explain the origin of life by separating it from the general development of matter. They regarded it as a sudden act of spontaneous -generation of organisms which, though themselves primitive, were still endowed with all the complicated attributes of life. This approach to a solution of the question was, however, found to be radically inconsistent with the results of experiment and observation and could therefore lead to nothing but bitter disappointment. A completely different prospect opens out before us if we try to approach a solution of the problem dialectically rather Xll INTRODUCTION than metaphysically, on the basis of a study of the successive changes in matter which preceded the appearance of life and led to its emergence. Matter never remains at rest, it is constantly moving and developing and in this development it changes over from one form of motion to another and yet another, each more complicated and harmonious than the last. Life thus appears as a particular very complicated form of the motion of matter, arising as a new property at a definite stage in the general development of matter. As early as the end of last century Frederick Engels indicated that a study of the history of the development of matter is by far the most hopeful line of approach to a solution of the problem of the origin of life. These ideas of Engels were not, however, reflected to a sufficient extent in the scientiftc thought of his time. Even in the first decades of this century only a very few of the leading scientists came out in support of the idea that life originated as the result of an evolutionary process. Their pronouncements were, however, still of a very general character and could not overcome the stagnation in the scientific fields concerned with the problem of the origin of life. Scientists have acquired a large number of facts during the twentieth century and it is only on the basis of these that we have now, at last, been able to draw a schematic picture of the evolutionary development of matter and set out the stages through ^vhich it must successively have progressed on the way to the emergence of life. As a result of this, wide possibilities for experimental work on the problem of the origin of life have been opened up. This time, though, interest was not focussed on hopeless attempts to discover instances of spontaneous generation but on the study and experimental reproduction of phenomena which were not merely possibilities but were completely subject to natural laws and took place successively in the evolutionary development of matter. This situation gave rise to a complete recasting of the ideas of scientists in relation to the problem of the origin of life. During the course of nearly all the first half of the twentieth century this problem was almost entirely excluded from the domain of science and it only received an insignifi- INTRODUCTION Xlll cant amount of space in the scientific literature of the world. Now, however, large numbers of books, articles, reviews and exj>erimental papers are already being devoted to it. To-day we are not satisfied by any merely speculative interpretation of the history of the phenomena which have occurred at some time or another on our planet. We must check our knowledge by experiment. We must reproduce experimentally the separate stages in the historical development of matter and finally create life again, synthetically, not by the long and devious route by which this synthesis took place in nature, but by a route based on a thorough understanding of those forms of organisation which we find already in a finished state in existing living things. This task is certainly exceptionally complicated but con- temporary science has indications upon which it can, at least, make an estimate of the work in real terms. In what follows I shall do my best to make clear the ways in which human minds have tried to solve the problem of the origin of life. I shall give a short account of the numerous doctrines and theories which have been formed during many centuries, but I shall devote the greater part of my attention to drawing a picture of the progressive development of matter which, in my opinion, led up to the emergence of life on our planet. CONTENTS Preface ... ... ... ... v Translator's Preface ... ... ... vii Introduction ... ... ... ix Chapter I THEORIES OF THE SPONTANEOUS GENERATION OF LIFE Ancient and mediaeval beliefs .. . ... ... ... i Redi's experiments ... ... ... ... ... 17 Hypotheses concerning the spontaneous generation of microbes... ... ... ... ... ... 19 The work of Pasteur ... ... ... ... ... 28 Chapter II THE THEORY OF THE ETERNITY OF LIFE The theory of the eternity of life among the ancients ... 43 The emergence of hypotheses concerning the eternity of life in the nineteenth century ... ... ... ... 45 The theory of cosmozoe ... ... ... ... 53 Arrhenius' theory of panspermia ... ... ... 57 The state of the problem at the present day ... ... 60 XV 737I5 XVI CONTENTS Chapter III ATTEMPTS AT A SCIENTIFIC APPROACH TO THE PROBLEM OF THE ORIGIN OF LIFE The mechanistic concept of the self-formation of living things ... ... ... ... ... ... 73 The views of Haeckel and Pfliiger ... ... ... 77 Attempts to construct ' models of living organisms ' ... 86 The evolutionary theory of the origin of life ... ... gs> Chapter IV THE ORIGINAL FORMATION OF THE SIMPLER ORGANIC SUBSTANCES The question of the original formation of organic substances ... ... ... ... ... ... 107 The distribution of organic substances (hydrocarbons) on different heavenly bodies ... ... ... ... 115 Geological finds of hydrocarbons formed abiogenically on the Earth ... ... ... ... ... 125 Theory of the origin of the Earth ... ... ... 131 Ways in which organic compounds could have arisen during the formation of the Earth ... ... 136 Chapter V ABIOGENIC ORGANIC CHEMICAL EVOLUTION OF CARBON COMPOUNDS Thermodynamics and kinetics of the transformation of the simplest hydrocarbons in the lithosphere, atmosphere and hydrosphere of the Earth ... ... ... 153 Reducing conditions ... ... ... ... ... 158 CONTENTS Xvii Sources of energy ... ... ... ... ... 161 The origin of carbohydrates, lipids, porphyrins, amino acids, nucleotides, polynucleotides and protein-like polypeptides ... ... ... ... ... 189 Chapter VI THE STRUCTURE AND BIOLOGICAL FUNCTIONS OF PROTEINS AND NUCLEIC ACIDS AND THE PROBLEM OF THEIR ORIGIN Chemical structure and biological functions of polypeptides and proteins ... ... ... ... ... 229 The amino acid composition and sequence in the structure of the macromolecules of proteins ... ... ... 236 Hormones, enzymes, antibiotics and antigens ... ... 243 The biosynthesis of proteins ... ... ... ... 259 Chapter VII THE DEVELOPMENT OF ORGANIC MULTIMOLECULAR SYSTEMS: THEIR ORGANISATION IN SPACE AND IN TIME Simple and complex coacervates ... ... ... goi The structure and properties of complex coacervate drops 307 Points of similarity between complex coacervates and protoplasm ... ... ... ... ... si 1 Stationary open systems ... ... ... ... 321 The thermodynamics and kinetics of open systems ... 323 The initial systems from which living things arose ... 335 XVUl CONTENTS Chapter VIII THE ORIGIN OF THE FIRST ORGANISMS The evolution of the initial systems ... ... ... 347 The principle of selection ... ... ... ... 349 Processes of self-renewal of the systems ... ... ... 354 The origin of the capacity of the systems for self-preservation and growth ... ... ... ... ... 356 The origin of the highly dynamic state of the systems ... 358 The origin of systems capable of reproducing themselves 359 The evolution of metabolism: the origin of enzymes ... 363 The origin of the co-ordinated networks of reactions: the origin of the first organisms ... ... ... 374 Chapter IX THE FURTHER EVOLUTION OF THE FIRST ORGANISMS The concept of comparative biochemistry The first living things—heterotrophs and anaerobes Different forms of energy metabolism ... Photochemical reactions The formation of free oxygen Chemosynthesis Photosynthesis The origin of respiration Conclusion ... Index 397 399 419 438 448 450 455 464 487 491

INTRODUCTION XI This led to a serious crisis in the ideas of many scientists of our century concerning the problem with which we are dealing. Some of these scientists tried to get out of the question by suggesting that life never arose on Earth but that the first living things were brought here from somewhere else such as the surface of one of the nearer or more distant planets. Others got round the question of the origin of life by adopting openly idealistic positions and declaring that the problem belonged, not to the province of science but to that of faith. It was, of course, not the nature of the problem which led to this crisis but the fact that scientists were using faulty methods in their approach to it. It was the outstanding service of Charles Darwin to biology that he broke with the earlier metaphysical methods for attacking the problem of the origin of the existing forms of animals and plants. He showed, beyond question, that highly organised living creatures can appear on the Earth only as the result of prolonged development, that is, evolution of higher forms from lower ones. In the absence of such evolution it was impossible to maintain that human beings or