A. I. Oparin - The Origin of Life
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This is a translation by Ann Synge of A.I. Oparin, (1924) Proiskhozhdenie zhizny.
Moscow. Izd.Moskovhii RabochiI.
The Origin of Life
A. I. Oparin
Grau, teurer Freund, ist alle Theorie, Und grün des Lebens goldener Baum. GOETHE
The Theory of Spontaneous Generation EVER since he took the first steps towards a conscious life, Man has tried to solve the problems of cosmogony. The most complicated and also the most interesting of these is that of the origin of life. At different times and at different stages of culture different answers have been given. The religious teachings of all ages and peoples have usually attributed the appearance of life to some creative act by a deity. The first students of nature were very naïve in their answers to this question. Even to a man of such outstanding intelligence as Aristotle in ancient times, the idea that animals, including worms, insects and even fish, could develop from mud presented no special difficulty. On the contrary, this philosopher maintained that any dry body becoming moist or, on the other hand, any wet body becoming dry, would give rise to animals.
The authority of Aristotle had an exceptionally strong influence on the outlook of men of learning in the Middle Ages. In their minds the ideas of this philosopher became interwoven with the doctrines of the fathers of the Church, often giving rise to suppositions which, to our eyes, appear stupid or even ridiculous. In the Middle Ages it was held that although the preparation of a living person, or of something like one in the form of a “homunculus”, in a retort by the mixing and distillation of various chemical substances was extremely difficult and impious, nevertheless it was undoubtedly something which could be done. The production of animals from non-living materials seemed to the scientists of those times to be so simple and ordinary that the well- known alchemist and doctor, van Helmont, actually gave a receipt according to which it was possible to prepare mice artificially by placing damp grain and dirty rags in a covered vessel.
There are a number of writings from the sixteenth and seventeenth centuries describing the transformation of water, stones and other inanimate objects into reptiles, birds and beasts. Grindel von Ach even gives a picture of frogs formed from May dew, while Aldrovandi gives drawings which show how birds and insects arise from the twigs and fruit of trees.
The idea that the maggots in rotting meat, fleas in dung and intestinal worms are generated spontaneously from decaying materials was generally accepted as an unalterable truth which was in full accord with Holy Writ. Also, in the writings of those times, we often meet with numerous texts by means of which the authors hope to convince their readers that the theory of spontaneous generation has the full support of the Bible.
However, the further science developed and the more the study of nature came to involve the use of accurate observations and experiments rather than just argument and philosophizing alone, the narrower became the region in which the learned men believed that spontaneous generation could occur.
As early as the middle of the seventeenth century Redi demonstrated by simple experiments that there was no basis for the opinion that spontaneous generation of maggots takes place in rotting meat. He covered the meat with a thin gauze and thus made it inaccessible to those flies from whose eggs the maggots would develop. Under these conditions the meat putrefied but no maggots whatsoever appeared. It was as simple as that to refute the idea of spontaneous generation of insects.
Thus, so far as living things visible to the naked eye were concerned, the theory of spontaneous generation had no support. However, at the end of the seventeenth century Kircher and van Leeuwnhoek discovered a world of tiny creatures, invisible to the naked eye, and only discernible with the microscope. These “tiny living beasties” (as van Leeuwnhoek called the bacteria and infusoria which he had discovered) were to be found wherever decay was taking place; in decoctions and infusions of plants which had been allowed to stand for a long time, in decaying meat and broth, in sour milk, in dung and in the fur on teeth. “There are more of them (microbes)”, wrote van Leeuwnhoek, “than there are people in the United Provinces”. It was only necessary for a substance which sours quickly and decays easily to stand for some time in a warm place for microscopic living creatures which had not been there before to develop in it immediately. Where did these creatures come from? Had they really arisen from germs which had happened to fall on the decaying material? How many of these germs there would then have to be everywhere. The idea inevitably arose that it was indeed in the rotting decoctions and infusions that the spontaneous generation of living microbes from non-living material took place. This view received strong support in the middle of the eighteenth century from the work of the Scottish clergyman Needham. He used meat broth or decoctions of vegetable material which he placed in completely closed vessels and boiled for a short while. By doing this Needham reckoned that he must have destroyed all the germs which were present and new ones could not get in from outside because the vessels were completely covered. Nevertheless, after a short while microbes appeared in the liquids. From this demonstration Needham drew the conclusion that he was witnessing the phenomenon of spontaneous generation.
However, there was another learned man who opposed this view. He was the Italian, Spallanzani. He repeated Needham’s experiments and became convinced that more prolonged heating of the vessels containing the organic liquids sterilized them completely. A bitter quarrel raged between the proponents of the two opposite viewpoints. Spallanzani showed that, in Needham’s experiments, the liquids had not been heated enough and that the germs of living things were still
present in them. Needham retorted that it was not he who heated his liquids too little, on the contrary, Spallanzani heated his too much and by such rough treatment destroyed the “generative power” of the organic which was very tricky and unstable.
Thus, each of the contestants stuck to this opinion and the question of the spontaneous generation of microbes in putrefying liquids was not solved one way or the other for a whole century. During this time quite a large number of attempts were made to prove or disprove by experiment the occurrence of spontaneous generation, but none of them gave a definitive result. The question became more and more embroiled and it was not until the middle of the nineteenth century that it was finally solved by the studies of a French scientist of genius – Pasteur. Pasteur first showed the extremely wide distribution of microbes. In a series of experiments he showed that everywhere, but especially near human habitations, the air contains tiny germs. They are so light that they float freely in the air, only falling to the ground ver slowly. On the slightest breeze they fly up again and are carried around us invisibly. The air of large towns is positively swarming with these crumbs of life. A single cubic metre of the air in Paris in summer contains up to 10.000 viable germs. If they encounter favourable conditions they grow, develop and begin to multiply at an extraordinary speed causing the decomposition of liquids which putrefy easily. Thus, it is not the putrescent liquids which give rise to the microbes but the microbes falling from the air which cause the putrefaction of the liquids. Pasteur explained the mysterious appearance of micro-organisms in the experiments of earlier authors being due to incomplete sterilization of the medium of insufficient protection of the liquids against the access of the germs which might enter it with the air, the, in a hundred per cent of cases, there will be no putrefaction of the liquid and no formation of microbes.
Pasteur used a great variety of devices for sterilizing the air entering his retorts. He sometimes heated it in red-hot tubes of metal or glass; sometimes the neck of the flask was plugged with cotton wool in which all the minute particles carried in the air were trapped; or finally, sometimes the air was passed through a fine glass tube shaped like the letter S, in which case all the germs were trapped mechanically on the damp surfaces of the curves of the tube. Whenever the precautions were sufficiently reliable the appearance of microbes in the liquid was not observed. Maybe, however, the prolonged heating had changed the medium chemically and made it unsuitable for supporting life. Pasteur easily refuted this suggestion. He dropped into the sterilized liquid the cotton-wool plug through which air had passed into the retort and which therefore contained germs. The liquid quickly putrefied. The boiled liquid was, thus, a perfectly suitable soil for the development of bacteria. The only reason why this development did not occur was the absence of seed in the form of germs. As soon as the germs fell in the liquid they began to grow at once and gave a good harvest.
Finally, Pasteur succeeded in showing that it is possible to keep such easily putrefied liquids as blood and wine for long periods even without any heating. It was only necessary to remove them from the animal (where they do not contain bacteria) aseptically, that is, taking precautions against bacteria falling into them from outside. Thus, Pasteur’s experiments showed beyond doubt that the spontaneous generation of microbes in organic infusions does not occur.
All living organisms develop from germs, that is to say, they owe their origins to other living things. But how did the first living things arise? How did life originate on the Earth? In what follows theories will be examined which attempt to solve this problem.
The Theory of Panspermia Pasteur is rightly considered as the father of the science of the simplest organisms, i.e. microbiology. His work gave the impetus to extensive studies of a world of minute creatures, invisible to the naked eye but inhabiting the earth, water and air. The investigations undertaken were not now, as formerly, directed merely towards describing the form of the micro-organisms; bacteria, yeasts, infusoria, amoebae, etc., were studied from the point of view of the conditions necessary for their life, their nutrition, respiration and multiplication; from the point of view of the changes which they bring about in their environment and finally from the point of view of their internal structure in its finest details. The further these studies proceeded the clearer it became that the simplest organisms were by no means so simply constructed as had once been thought.
The body of any organism, whether it be plant, mollusc, worm, fish, bird, beast or man is made up of very small droplets which are only visible under the microscope. It is built up from these droplets or cells as a house is built of bricks. The various organs of different animals and plants are composed of cells of different sorts. In becoming adapted to the work carried out by a particular organ the cells of which it is composed are changed in one way or another but, essentially and in principle, all the cells of all organisms are alike. Micro-organisms differ only in that their whole bodies consist of a single cell. This similarity in principle between all organisms confirms the idea, now generally accepted in scientific circles, that all living things on the Earth are connected with one another; they form, so to speak, a family of blood relations. The more complicated organisms arose from simpler ones which gradually changed and grew more efficient. Thus, it is only necessary to explain how some very simple organism could have been formed in order to be able to understand the origin of all plants and animals.
However, as has already been said, even the simplest creatures, consisting of only one cell, are extremely complicated structures. Their main component, called protoplasm, is a semi-liquid, ductile, gelatinous substance, permeated with water but not water soluble. Protoplasm is made up of a large number of extremely complicated chemical substance (mainly proteins and their derivatives) which are never found except in organisms. These substances are not simply mixed but are in a special state which has not yet received much study. Owing to this the protoplasm has an extremely fine structure which is poorly differentiated even under the microscope, but is extraordinarily complicated. The idea that such a complicated structure with a completely determinate fine organization could arise spontaneously in the course of a few hours in structureless solutions such as broths or infusions is a wild as the idea that frogs could be formed from the May dew or mice from corn. The extreme complexity of the structure of even the simplest organisms struck some scientists so forcibly that they were sure that an
impassable abyss existed between the living and the dead. The transition from dead to living or organized seemed impossible, either in the present or in the past. “The impossibility of spontaneous generation at any time whatever”, writes the well-known English physicist W.Thomson, “must be considered as firmly established as the law of universal gravitation”.
How then did life appear on the Earth? There was a time when, according to the views now generally accepted among scientists, the Earth was a white-hot ball. Astronomy, geology, mineralogy and other exact sciences provide evidence for this and it is beyond doubt. This means that conditions on the Earth are such that it was unthinkable, not to say impossible, for life to exist on it. Only after the Earth had lost a considerable amount of its heat by dissipating it in the cold of interplanetary space, and the cooling had gone so far that the water vapour had formed the first hot seas, did the existence of organisms like those we now see become possible. In order to explain this contradiction a theory was evolved which bore the rather complicated name of “panspermia”.
H.e. Richter was the originator of this theory. Starting from the hypothesis that everywhere in space there are small particles of solid material (cosmozoa) which have been cast off by celestial bodies, the author suggested that along with these particles and possibly attached to them, there were the germs of micro-organisms. Thus these germs could be carried from one celestial body which was not yet inhabited by organisms to another which was not yet inhabited. If on this body the conditions of temperature and moisture were suitable for life, then the germs would begin to grow and develop and would be the original parents of all the organic creatures on the planet concerned. This theory attracted many supporters in the world of science, among them such outstanding minds as those of Helmholtz and W.Thomson. Its proponents were mainly concerned to demonstrate scientifically the possibility of such a transfer of germs from one heavenly body to another with conservation of their viability. In fact, when all was said and done, the main question was whether or not spores could complete such a long and dangerous journey as a flight from one planet to another without being destroyed and while retaining the ability to grow and develop into a new organism. Let us examine closely what dangers the germ would meet on the way. In the first place there is the cold of interplanetary space, about – 220º C. Having been cast off from its home planet the germ would be doomed to spend long years, centuries or even millennia at such an appalling temperature before some lucky change would give it the possibility of arriving in a new world. The question inevitably arises as to whether the germ could survive such an ordeal. To solve this problem experiments were made on the resistance to cold of present-day spores. Experiments along these lines showed that spores tolerate cold excellently. They remain viable even after having been kept at –220º C for six months. Of course, six months is not 1.000 years but, all the same, this experiment give us reason to suppose that at least some spores could stand the severe cold of interplanetary space. A far more severe danger to germs is presented by their complete lack of protection from light rays. Their path between the planets is penetrated by the rays of the Sun which are destructive to most microbes. Some bacteria are destroyed by the action of direct sunshine after only a few hours while others are more stable, but all, without exception, are unfavourably affected by very strong irradiation. This unfavourable effect is, however, considerably mitigated when there is no oxygen in the atmosphere, and we know that there is no air in space so we have some reason to suppose that germs of life could survive even this ordeal.
But let us assume that a lucky chance has given our germ the opportunity of falling into the gravitational field of some planet on which the conditions of temperature and moisture are favourable for the development of life. It remains only for the wanderer to submit to the gravitational force and to fall on its new land. But here, at once, just as it is reaching its destination in space, a terrible danger awaits it. Before this germ had been in air-free space, but before it can arrive at the surface of the planet it must pass through a fairly thick layer of air which surrounds its planet on every side.
The phenomenon of “falling stars” (or meteorites) must be well known to everyone. Scientist now explain this phenomenon as follows: there are, floating in interplanetary space, lumps of material of greater or lesser size, fragments of planets or comets which have flown into our solar system from distant parts of the Universe. When they pass close to the Earth they are attracted to it, but before they can fall on it they have to pass through the atmosphere. Owing to the friction of the air the quickly falling meteorite becomes heated to white heat and becomes visible against the dark vault of the sky. Only a few of these meteorites reach the Earth in the form of red-hot stones from the sky. Most of them get burnt up by the intense heat long before they reach its surface. A similar fate must befall the germs. However, various
considerations indicate that destruction of this sort need not necessarily occur. There is reason to suppose that at least some of the germs reaching the atmosphere of any planet would reach its surface in a viable state.
Furthermore, there is no need to dwell on colossal, astronomical periods of time during which the Earth could have been sown with germs of life from other worlds. These periods are reckoned in millions of years. If, during this period, even one of the thousands of millions of germs could have reached the surface of the Earth satisfactorily and found there conditions suitable for its development, then this would be enough for the formation of the whole organic world. All the same, in the present state of scientific knowledge, this possibility, though conceivable, seems not to be very probable. ∗ In any case we have no facts which would directly contradict it. However, the theory of panspermia is only the answer to the problem of the origin of earthly life, and not in any way to that of the origin of life in general. Carus Sterne writes: “If this hypothesis merely pushes the beginning of life backwards to the time of the first appearance in the world of celestial space, then, from the philosophical point of view it is a ∗ Even such an out-and-out defender of the theory under discussion as Helmholtz says in this connection, “I cannot deny it if anyone thinks that this hypothesis is not very probable or even in the highest degree improbable”. And he adds further that he is forced to take up the point of view of the theory of panspermia because of the complete impossibility of explaining the origin of life scientifically in any other way. completely useless labour because whatever could have happened in the first world was also possible in the second and third and would be the act of creation or spontaneous generation”.
“There are two possibilities”, said Helmholtz, “organic life either began (came into being) at some time or else it has always existed”. If we accept the former view, then the theory of panspermia loses all logical point, for, if life could originate at some point in the Universe, there is no reason to suppose that it could not originate on the Earth as well. The partisans of the theory under discussion therefore accept the theory of the eternity of life. They recognize that “life can only change its form, it can never be created from dead material”. Thus they put an end once and for all to any further study of the problem of the origin of life. They try to set up an impassable barrier between the living and the dead and to impose a limit on the efforts of the human mind and on the boundless generalizations to which exact science leads it.
But do we have any logical right to accept the fundamental difference between the living and the dead? Are there any facts in the world around us which convince us that life has existed for ever and that it has so little in common with dead matter that it could never, under any circumstances have been formed or derived from it? Can we recognize organisms as formations which are entirely and essentially different from all the rest of the world? We shall try to give an answer to these questions in the next chapter. The World of the Living and the World of the Dead The first and most eye-catching difference between organisms and the rest of the (mineral) world is their chemical composition. The bodies of animals, plants and microbes are composed of very complicated, so- called organic substances. With very few and insignificant exceptions we do not find these substances anywhere in the mineral world. Their main peculiarity consists in the fact that at high temperatures in the presence of air they burn while in the absence of air they carbonize. This shows that they contain carbon. This element is present in all organisms without exception. It forms the basis of all those substances of which protoplasm is made up. At the same time, however, it is no stranger to the mineral world.
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